Mechanical Engineering

Globe valves and gate valves are used for different applications. This article discusses about the topic globe valve vs gate valve in detail.

Globe valves are used for regulating the flow whereas the gate valve is used to completely shut off the flow. Lets see more differences in detail in further sections of this article.

What is a globe valve?

A globe valve is a type of control valve that is used for regulating or controlling the flow in a pipeline.

It is different from a ball valve. It consists of movable plug and a stationary ring seat fitted generally inside a spherical body.

Image credits: Wikipedia

What is a ball valve?

A ball valve is also a type of control valve that is used to regulate or control the flow in pipeline.

It is different from a globe valve. It has a hollow or perforated ball which is used for controlling the flow of fluid in the pipeline.

Where is a globe valve used?

Globe valve finds its applications in more areas than a gate valve does as it can be used for regulating flow and pressure as well.

Globe valves are most commonly used in plant piping. They can be used as a pressure relief valve or a check valve and they are also suitable for manual and automatic operations.

Which is better gate valve or ball valve and why?

A gate valve may be cheaper but it has many disadvantages over ball valve. So application wise, ball valve is superior than a gate valve. Although in high pressure applications, gate valve is desired more. Lets see why.

• Gate valves are susceptible to corrosion, whereas ball valves are less likely to undergo such process.
• Ball valves provide a tighter seal and prevents leakage.
• A gate valve is superior in high pressure applications because ball valve has short opening and closing time which results in water hammer.

How do I know if my globe valve is open or closed?

A globe valve consists of a stem, bonnet and plug. The relative positions of these can determine whether the globe valve is open or not.

If the stem is completely inside bonnet, then the plug will rest on body where a hole is given for the water to flow. This means the globe valve is closed. If the stem rises from the bonnet then it is in open condition.

To open or close, one has to rotate the handle as done with screws.

Can globe valve be used for isolation?

First we need to understand what is isolation valve, it is simply a valve that can stop the fluid flow process to given location.

A typical globe valve can be used for lowering the pressure as well as isolation purposes. But globe valves show higher pressure drop than straight through valves (I.e ball valve, gate valve etc). So, a globe valve can be used for isolation when pressure drop is not a controlling factor of the flow.

Can a gate valve fail?

Absolutely yes. Every mechanical component has a life expectancy and so does a gate valve. Following are the cases where it can fail-

• Most commonly it fails due to wear and corrosion.
• Jamming of a gate valve takes place if not used for quite some time.
• Freezing of bonnet can break the valve resulting in massive flooding.
• Some amount of liquid can leak through the seats so that leakage factor has to be kept in mind.

When would you use a gate valve?

Normally gate valves are used when the liquids need to be shut off rather than being regulated.

Gate valves can be used in following scenarios-

• When liquid needs to shut off.
• When minor leakage of liquid is not an issue (eg. Heater circuits and sewer pipes etc.)
• Low pressure applications where friction won’t be significant.

Can a gate valve reduce pressure?

Yes, a gate valve can reduce pressure if a bypass controller is attached to it.

The gate valves with larger diameters are fitted with a bypass controller. This way the pressure is reduced by a significant value before even reaching the valve itself. Pressure is reduced because in high pressure, the friction becomes a significant problem.

How can you tell if a gate valve is open or closed?

There is no visual indicator that indicates whether the gate valve is open or closed. However, the position of knob can be used to determine whether the valve is open or closed.

A gate valve consists of a knob which when rotated counter clockwise, opens the valve and closes when turned clockwise. As it opens the valve, knob rises up indicating that the valve is open and closed when the knob is resting on the bonnet.

Is globe valve a control valve?

A globe valve can be called as a control valve.

Globe valve can be used to regulate or completely stop the flow making it a control flow valve.

Is globe valve unidirectional?

Yes, a globe valve is unidirectional. Unidirectional means that it allows flow in only one direction, it cannot change the direction of the flow completely.

When compared to other valves, only gate valve is bi directional whereas globe and check valves are uni directional.

How do you free up a gate valve?

A gate valve can be jammed if not used over several years. It has to be tested after certain period of time else it will be damaged and we would not even know.

To open up a jammed valve, we can simply try moving the knob back and forth slowly with a plier. This way the jamming will open up gradually. Remember not to do it very fast else it might get damaged.

Can you adjust a gate valve?

It is very easy to adjust a gate valve or rebuild it again after dismantiling it. First we check the position till where the knob goes inside.

If the knob goes completely inside then the valve need not be fixed. If it goes upto only a certain length, then we will have to flush it out. Flushing means getting rid of excessive or unwanted materials lying inside the valve. This can be done by loosening one of the screws in the body.

What are the advantages and disadvantages of gate valve?

Each and every mechanical component has its own advantages and disadvantages.

The advantages of gate valves are-

• They have very less fluid resistance–  The shape of this valve allows the fluid to flow with minimal fluid resistance.
• They have a leak proof seal- The opening and closing mechanism of this valve are superior than shut off valves.
• They have wide range of applications- Gate valves can be used for oils, steam or even granular solids like Alumina. They can be fond in a wide range of applications.
• Gate valves are bidirectional- Unike globe valves, as discussed above, gate valves are bi-directional meaning they allow dual fluid flow directions.

The disadvantages of gate valves are-

• The closing and opening speed of these valves is very slow– This particular disadvantage makes this valve undesirable for applications requiring rapid actions.
• These valves can get scratches easily- Scratches may seem normal but eventually they grow and affect sealing capability of the valve.

How many turns does it take to open a gate valve?

Number of turns required for closing or opening a gate valve can be found out using the AWWA formula.

Number of turns is equal to three times the nominal valve size plus two or three turns of the operating nut.

For example 5 x 3= 15 plus 2 or 3= 17 or 18 turns.

Function of globe valve and gate valve

The function of globe valve and gate valve are given in the table as shown below-

Globe valve	Gate valve
Regulates, starts and stops the flow of fluid.	Used for completely shutting off flow of fluids rather than regulating.
Can be used as ON/OFF valve.	Used in heating circuits and sewer piping.
Can be used for throttling purposes.	They are used with large pipe diameters because they are easy to construct.

Globe valve types

The term globe doesnt necessarily mean that the valve will have a round shape. In addition to that, it comes in various types. They are-

• Tee-This is the most common type of globe valve. They are used in throttling purposes. The horizontal design of the seat allows the stem as well as disk to travel perpendicular to the horizontal plane.
• Angle-The name suggests that there is an angular turn inside this valve which is true. The ends of this valve are at ninety degrees allowing the flow to flow in a perpendicular direction to handle the slugging effect.
• Wye-This valve is an alternative for high pressure drop found in globe valves. The angle between seat and stem are forty five degrees which provides a better flow path with lesser resistance to flow.

Globe valve vs butterfly valve

The differences between a globe valve and butterfly valve are given below-

Globe valve	Butterfly valve
The disc of the globe moves in a straight line.	Butterfly valve has a plate shaped disc that rotates around its own axis.
Main parts are bonnet, stem, body and handwheel.	Main parts are valve body, stem, butterfly plate and sealing ring.
Can be used for cutting off or regulating the flow of fluid.	It is used for flow regulation mostly for throttling purposes.

How does a gate valve work?

These valves work by inserting a gate (mostly rectangular) or wedge between the path of flow. This plate is actuated by threaded stem which itself is actuated by hand or electric motor.

How does a directional valve perform in three functions?

A directional valve is designed to work only in three functions.

The three functions in which the directional valves work are- stop the fluid flow, start the fluid flow or change the direction of fluid flow.

How do you lubricate a ball valve?

Lubrication is necessary else the ball inside the ball valve will jam and the valve will be rendered useless.

We can lubricate the ball valve by spraying penetrating lubricant around the ball valve handle precisely between the coloured handle and the pipe portion of the ball valve. After applying lubricant, turn the knob back and forth so that the lubricant can pass through the tight crack and enter the body of the valve.

This way the lubricant can penetrate inside and lubricate internal components of the valve too.

The saturated suction temperature is an important concept in the field of refrigeration and air conditioning. It refers to the temperature at which the refrigerant vaporizes completely in the evaporator coil. This temperature is crucial because it determines the efficiency and performance of the cooling system. By maintaining the correct saturated suction temperature, the system can effectively remove heat from the desired space. Understanding the saturated suction temperature is essential for technicians and engineers involved in designing, installing, and maintaining refrigeration and air conditioning systems. In this article, we will explore the significance of saturated suction temperature and its impact on system performance. We will also discuss the factors that affect the saturated suction temperature and how it can be controlled to optimize system efficiency. So, let’s dive in and uncover the world of saturated suction temperature in refrigeration and air conditioning systems.

Key Takeaways

• Saturated suction temperature refers to the temperature at which the refrigerant vaporizes completely in the evaporator coil.
• It is an important parameter in refrigeration systems as it affects the cooling capacity and efficiency.
• The saturated suction temperature is determined by the pressure and the refrigerant being used.
• Proper monitoring and control of the saturated suction temperature is crucial for maintaining optimal system performance.
• Deviations from the desired saturated suction temperature can indicate issues such as low refrigerant charge or improper airflow.

Saturated Suction Temperature

The saturated suction temperature is a crucial parameter in refrigeration systems that plays a significant role in determining various key parameters. In this section, we will explore the definition and concept of saturated suction temperature, its relationship with system pressure, and its role in determining important parameters of a refrigeration system.

Definition and Concept

The saturated suction temperature refers to the temperature at which the refrigerant vaporizes completely in the evaporator coil of a refrigeration system. It is the temperature at which the refrigerant changes from a liquid state to a vapor state. This temperature is directly related to the pressure at which the refrigerant is maintained in the evaporator coil.

Relationship between System Pressure and Saturation Temperature

The saturated suction temperature is closely related to the system pressure in a refrigeration system. As the pressure increases, the saturation temperature also increases, and vice versa. This relationship is governed by the pressure-temperature relationship of the refrigerant being used.

For example, if we consider a refrigerant with a low-pressure range, such as R-134a, an increase in system pressure will result in an increase in the saturated suction temperature. On the other hand, refrigerants with a high-pressure range, like R-410A, will exhibit a similar relationship between pressure and saturation temperature.

Role of Saturated Suction Temperature in Determining Key Parameters of a Refrigeration System

The saturated suction temperature plays a crucial role in determining various key parameters of a refrigeration system. Let’s explore some of these parameters:

1. Superheat: The saturated suction temperature helps determine the superheat of the refrigerant vapor leaving the evaporator coil. Superheat refers to the temperature rise of the refrigerant vapor above its saturation temperature. It is an important parameter that ensures the complete evaporation of the refrigerant before it enters the compressor.

2. Subcooling: The saturated suction temperature also influences the subcooling of the liquid refrigerant leaving the condenser. Subcooling refers to the temperature drop of the liquid refrigerant below its saturation temperature. It helps improve the efficiency of the refrigeration system by ensuring that the liquid refrigerant is at a lower temperature than the surrounding environment.

3. Compressor Efficiency: The saturated suction temperature directly affects the efficiency of the compressor. A higher saturated suction temperature can lead to decreased compressor efficiency due to increased power consumption and reduced cooling capacity. On the other hand, maintaining a lower saturated suction temperature can improve the overall efficiency of the system.

4. Heat Transfer: The saturated suction temperature influences the heat transfer process within the evaporator coil. By maintaining an optimal saturated suction temperature, the refrigeration system can efficiently absorb heat from the surroundings and provide effective cooling.

5. Condensing Temperature: The saturated suction temperature indirectly affects the condensing temperature of the refrigerant. A higher saturated suction temperature can result in a higher condensing temperature, which may impact the overall performance and efficiency of the system.

6. Evaporating Temperature: The saturated suction temperature is an indicator of the evaporating temperature, which is the temperature at which the refrigerant absorbs heat in the evaporator coil. By controlling the saturated suction temperature, the system can maintain the desired evaporating temperature for efficient cooling.

In conclusion, the saturated suction temperature is a critical parameter in refrigeration systems that influences various key parameters such as superheat, subcooling, compressor efficiency, heat transfer, condensing temperature, and evaporating temperature. By understanding and controlling the saturated suction temperature, it is possible to optimize the performance and efficiency of a refrigeration system.

Suction Temperature

The suction temperature plays a crucial role in the efficient operation of a refrigeration system. It is important to understand the definition and significance of suction temperature in order to optimize the performance of the system. Additionally, the ideal temperature in relation to saturation temperature and system pressure is a key factor to consider. Let’s delve deeper into these aspects.

Definition and Significance in a Refrigeration System

The suction temperature refers to the temperature of the refrigerant vapor as it enters the compressor’s suction line. It is a critical parameter that directly affects the performance and efficiency of the entire refrigeration system.

In a refrigeration cycle, the compressor’s main function is to compress the refrigerant vapor, raising its pressure and temperature. The suction temperature determines the state of the refrigerant entering the compressor. If the suction temperature is too high, it can lead to several issues, including decreased compressor efficiency, reduced cooling capacity, and potential damage to the compressor itself.

By monitoring and controlling the suction temperature, technicians can ensure that the refrigeration system operates optimally. This involves maintaining the suction temperature within a specific range, which is determined by factors such as the type of refrigerant used and the desired cooling requirements.

Ideal Temperature in Relation to Saturation Temperature and System Pressure

The ideal suction temperature is closely related to the saturation temperature and the system pressure. Saturation temperature refers to the temperature at which the refrigerant changes state from a liquid to a vapor or vice versa, while system pressure is the pressure at which the refrigerant operates within the system.

To understand the ideal suction temperature, it is important to consider the relationship between saturation temperature and system pressure. As the system pressure increases, the saturation temperature also rises. Conversely, as the system pressure decreases, the saturation temperature decreases as well.

The ideal suction temperature should be slightly lower than the saturation temperature at the corresponding system pressure. This temperature difference, known as superheat, ensures that only vapor enters the compressor, preventing any liquid refrigerant from causing damage. Superheat also helps to improve the efficiency of the heat transfer process within the evaporator coil.

On the other hand, if the suction temperature is too low, it can lead to a phenomenon called subcooling, where the refrigerant exists in a liquid state below its saturation temperature. Subcooling can negatively impact the overall efficiency of the system and result in poor heat transfer.

To calculate the ideal suction temperature, technicians use pressure-temperature charts specific to the refrigerant being used. These charts indicate the saturation temperature at various system pressures, allowing technicians to determine the appropriate suction temperature for optimal system performance.

In conclusion, the suction temperature is a critical parameter in a refrigeration system. By understanding its definition and significance, as well as its relation to saturation temperature and system pressure, technicians can ensure the system operates efficiently and effectively. Monitoring and controlling the suction temperature within the ideal range is essential for maintaining the overall performance and longevity of the refrigeration system.

Low Saturated Suction Temperature

A low saturated suction temperature in a refrigeration system can have various causes and implications. Understanding the importance of the degree of superheat in the refrigerant and the desired degree of superheat at the evaporator outlet and compressor suction is crucial for maintaining optimal system performance.

Causes and Implications of Low Suction Temperature

There are several factors that can contribute to a low saturated suction temperature in a refrigeration system. Some common causes include:

1. Insufficient refrigerant charge: If the system is undercharged with refrigerant, it can result in a low suction temperature. This occurs because there is not enough refrigerant flowing through the evaporator coil to absorb heat effectively.

2. Refrigerant restrictions: Any obstructions or restrictions in the refrigerant lines, such as clogged filters or blocked expansion valves, can lead to a decrease in the suction temperature. These restrictions limit the flow of refrigerant and reduce the system’s ability to transfer heat efficiently.

3. Inadequate airflow: Insufficient airflow across the evaporator coil can cause a decrease in the suction temperature. This can be caused by dirty or blocked air filters, malfunctioning fans, or improper ductwork design.

4. Faulty expansion valve: A malfunctioning or improperly adjusted expansion valve can result in a low suction temperature. If the valve is not allowing enough refrigerant to enter the evaporator coil, the suction temperature will be lower than desired.

A low saturated suction temperature can have several implications on the performance of a refrigeration system:

1. Reduced cooling capacity: A lower suction temperature means that the evaporator coil is not absorbing as much heat as it should. This results in reduced cooling capacity, leading to inadequate temperature control and potential spoilage of perishable goods.

2. Decreased compressor efficiency: The compressor is designed to operate within a specific range of temperatures. When the suction temperature is too low, the compressor may experience issues such as liquid refrigerant entering the compressor, which can cause damage and decrease its efficiency.

3. Poor heat transfer: With a low suction temperature, the temperature difference between the refrigerant and the surrounding air or water is reduced. This can result in poor heat transfer, making it harder for the system to remove heat from the conditioned space.

Importance of Degree of Superheat in Refrigerant

The degree of superheat in the refrigerant is a critical parameter that indicates the amount of heat absorbed by the refrigerant in the evaporator coil. It is defined as the temperature of the refrigerant vapor above its saturation temperature at a given pressure.

Maintaining the correct degree of superheat is essential for the efficient operation of a refrigeration system. Here’s why:

1. Prevents liquid refrigerant from entering the compressor: If the refrigerant entering the compressor contains liquid droplets, it can cause damage to the compressor and reduce its efficiency. By ensuring an adequate degree of superheat, the refrigerant is fully vaporized before entering the compressor, minimizing the risk of liquid carryover.

2. Maximizes heat transfer: The degree of superheat affects the efficiency of heat transfer in the evaporator coil. A proper degree of superheat ensures that the refrigerant absorbs enough heat to vaporize completely, optimizing the cooling capacity of the system.

Desired Degree of Superheat at Evaporator Outlet and Compressor Suction

The desired degree of superheat at the evaporator outlet and compressor suction depends on various factors, including the type of refrigerant, the design of the system, and the operating conditions. However, there are general guidelines to follow:

1. Evaporator outlet: The desired degree of superheat at the evaporator outlet typically ranges between 5 to 20 degrees Fahrenheit (2.8 to 11.1 degrees Celsius). This range ensures that the refrigerant is fully vaporized before entering the compressor, preventing liquid carryover.

2. Compressor suction: The desired degree of superheat at the compressor suction is usually higher than at the evaporator outlet. It is recommended to have a superheat of around 10 to 30 degrees Fahrenheit (5.6 to 16.7 degrees Celsius) at the compressor suction. This higher superheat helps to protect the compressor from any potential liquid refrigerant damage.

Maintaining the desired degree of superheat requires careful monitoring and adjustment of the refrigeration system. Regular inspections, proper refrigerant charging, and ensuring adequate airflow are essential for achieving and maintaining the optimal superheat levels.

In conclusion, a low saturated suction temperature can have various causes and implications in a refrigeration system. Understanding the importance of the degree of superheat and maintaining the desired superheat levels at the evaporator outlet and compressor suction are crucial for ensuring efficient system performance and preventing potential damage to the compressor.

Calculation of Saturated Suction Temperature

The saturated suction temperature is an important parameter in refrigeration systems as it directly affects the performance and efficiency of the system. There are different methods to calculate the saturated suction temperature, including the Clausius-Clapeyron equation and the use of a pressure-temperature equilibrium chart.

Clausius-Clapeyron Equation for Determining Saturated Suction Temperature

The Clausius-Clapeyron equation is a fundamental equation in thermodynamics that relates the temperature and pressure of a substance during a phase change. In the case of a refrigeration system, it can be used to determine the saturated suction temperature.

The equation states that the natural logarithm of the ratio of the vapor pressure at two different temperatures is equal to the enthalpy of vaporization divided by the gas constant, multiplied by the difference in inverse temperatures. Mathematically, it can be expressed as:

ln(P2/P1) = (ΔHvap/R) * (1/T1 – 1/T2)

Where:
– P1 and P2 are the vapor pressures at temperatures T1 and T2, respectively.
– ΔHvap is the enthalpy of vaporization.
– R is the gas constant.
– T1 and T2 are the temperatures at which the vapor pressures are measured.

By rearranging the equation, we can solve for the saturated suction temperature:

T2 = (1 / ((ln(P2/P1) * R / ΔHvap) + (1 / T1)))

This equation allows us to calculate the saturated suction temperature based on the known vapor pressures at two different temperatures.

Use of Pressure-Temperature Equilibrium Chart for Measurement

Another method to determine the saturated suction temperature is by using a pressure-temperature equilibrium chart. This chart provides a graphical representation of the relationship between the pressure and temperature of a refrigerant at its saturation point.

To use the chart, you need to know the pressure at the suction line of the refrigeration system. Locate this pressure on the chart and follow the corresponding line until it intersects with the saturation curve. The temperature at this intersection point is the saturated suction temperature.

The pressure-temperature equilibrium chart is a useful tool for quickly determining the saturated suction temperature without the need for complex calculations. It is commonly used by technicians and engineers in the field to troubleshoot refrigeration systems and ensure optimal performance.

In conclusion, the saturated suction temperature is a critical parameter in refrigeration systems. It can be calculated using the Clausius-Clapeyron equation or determined using a pressure-temperature equilibrium chart. Both methods provide accurate results and are widely used in the industry. By accurately measuring and controlling the saturated suction temperature, refrigeration systems can operate efficiently and effectively.

High Saturated Suction Temperature

When it comes to refrigeration systems, maintaining the right temperature is crucial for optimal performance. One important factor to consider is the saturated suction temperature. This refers to the temperature at which the refrigerant in the evaporator coil is completely vaporized, ready to be compressed by the compressor. In this section, we will explore the causes and consequences of high saturated suction temperature, the disadvantages of a higher degree of superheat in the refrigeration cycle, and the impact on compressor performance and system degradation.

Causes and Consequences of High Saturated Suction Temperature

A high saturated suction temperature can be caused by various factors, including improper refrigerant charge, inadequate airflow across the evaporator coil, or a malfunctioning expansion valve. When the suction temperature is higher than normal, it can have several consequences on the refrigeration system.

Firstly, a high saturated suction temperature can lead to a decrease in system efficiency. This is because the compressor has to work harder to compress the refrigerant vapor, resulting in increased energy consumption. Additionally, the higher temperature can cause the compressor to overheat, leading to reduced compressor lifespan and potential breakdowns.

Moreover, high saturated suction temperature can negatively impact the heat transfer process. When the refrigerant vapor exiting the evaporator coil is not fully vaporized, it can carry liquid droplets with it. These liquid droplets can cause issues such as reduced heat transfer efficiency, increased pressure drop, and potential damage to the compressor.

Disadvantages of a Higher Degree of Superheat in the Refrigeration Cycle

In a refrigeration cycle, superheat refers to the temperature of the refrigerant vapor above its saturation point. While a certain degree of superheat is necessary for proper refrigeration system operation, a higher degree of superheat can have disadvantages.

One disadvantage is reduced compressor efficiency. When the degree of superheat is too high, the compressor has to work harder to compress the vapor, resulting in increased energy consumption. This not only leads to higher operating costs but also puts additional strain on the compressor, potentially reducing its lifespan.

Another disadvantage is decreased cooling capacity. When the refrigerant vapor has a higher degree of superheat, it carries less heat energy. As a result, the evaporator coil may not be able to remove as much heat from the conditioned space, leading to reduced cooling capacity and potentially inadequate temperature control.

Impact on Compressor Performance and System Degradation

High saturated suction temperature can have a significant impact on compressor performance and overall system degradation. The compressor plays a crucial role in the refrigeration cycle by compressing the refrigerant vapor and increasing its pressure.

When the saturated suction temperature is high, the compressor has to work harder to compress the vapor. This increased workload can lead to higher energy consumption, reduced compressor efficiency, and increased wear and tear on the compressor components. Over time, this can result in decreased performance, increased maintenance requirements, and potentially premature compressor failure.

Furthermore, high saturated suction temperature can contribute to system degradation. The increased temperature can cause the refrigerant to break down and form acids, which can corrode the compressor and other system components. This corrosion can lead to refrigerant leaks, reduced system efficiency, and costly repairs.

In conclusion, maintaining the right saturated suction temperature is crucial for the optimal performance and longevity of a refrigeration system. A high saturated suction temperature can have various causes and consequences, including decreased system efficiency, reduced compressor lifespan, and potential system degradation. It is important to regularly monitor and control the saturated suction temperature to ensure the smooth operation of the refrigeration system.

Saturated Suction Temperature of Specific Refrigerants

The saturated suction temperature is an important parameter to consider when working with refrigeration systems. It refers to the temperature at which the refrigerant vaporizes completely in the evaporator coil of the system. Understanding the saturated suction temperature is crucial for maintaining the efficiency and performance of the refrigeration system.

Saturated Suction Temperature Chart for R404a

R404a is a commonly used refrigerant in commercial refrigeration systems. It is a blend of three refrigerants: R125, R143a, and R134a. To determine the saturated suction temperature for R404a, we can refer to a chart that provides the relationship between the pressure and temperature of the refrigerant.

The chart indicates that at a certain pressure, the saturated suction temperature of R404a will be a specific value. This information is useful for technicians and engineers who need to calculate the operating conditions of the system and ensure it is within the recommended range.

Here is an example of a saturated suction temperature chart for R404a:

Pressure (psig)	Saturated Suction Temperature (°F)
10	-20
20	-10
30	0
40	10
50	20

By referring to this chart, one can determine the saturated suction temperature of R404a based on the pressure reading in the system. This information is crucial for maintaining the proper operation of the refrigeration system and preventing any potential issues.

Saturated Suction Temperature for R134a and R410a

Apart from R404a, there are other refrigerants commonly used in refrigeration systems, such as R134a and R410a. These refrigerants also have specific saturated suction temperatures at different pressures.

For R134a, the saturated suction temperature can range from -20°F to 40°F, depending on the pressure in the system. It is important to note that as the pressure increases, the saturated suction temperature also increases. This relationship is crucial for maintaining the proper operation of the refrigeration system and ensuring efficient heat transfer in the evaporator coil.

Similarly, for R410a, the saturated suction temperature can range from -40°F to 50°F, depending on the pressure. It is important to monitor and control the saturated suction temperature to prevent any issues with the refrigeration system, such as insufficient cooling or compressor damage.

Understanding the saturated suction temperature of specific refrigerants is essential for maintaining the efficiency and performance of refrigeration systems. By monitoring and controlling this parameter, technicians and engineers can ensure optimal heat transfer, prevent compressor damage, and maintain the desired cooling capacity of the system.

Measurement and Calculation of Saturated Suction Temperature

The saturated suction temperature is a crucial parameter in refrigeration systems as it directly affects the efficiency and performance of the system. By accurately measuring and calculating the saturated suction temperature, technicians can ensure optimal operation and prevent any potential issues. In this section, we will explore the tools and methods used for measuring suction pressure and how PT charts can be utilized to determine the saturated temperature.

Tools and Methods for Measuring Suction Pressure

To measure the suction pressure accurately, technicians rely on specialized tools and methods. These tools enable them to obtain precise readings, allowing for accurate calculation of the saturated suction temperature. Here are some commonly used tools and methods:

1. Pressure Gauges: Pressure gauges are essential tools for measuring suction pressure. They are connected to the suction line of the refrigeration system and provide a reading in units such as psi or bar. Technicians can use these readings to calculate the saturated suction temperature.

2. Manifold Gauge Set: A manifold gauge set is a combination of pressure gauges, valves, and hoses. It allows technicians to measure both the suction pressure and the discharge pressure simultaneously. By comparing these readings, technicians can determine the temperature difference and calculate the saturated suction temperature.

3. Digital Thermometer: A digital thermometer is used to measure the temperature of the suction line. By placing the thermometer probe on the suction line, technicians can obtain an accurate reading of the suction line temperature. This reading, along with the suction pressure, can be used to calculate the saturated suction temperature.

Utilizing PT Charts to Determine Saturated Temperature

PT charts, also known as pressure-temperature charts, are valuable references for determining the saturated temperature of a refrigerant at a given pressure. These charts provide a graphical representation of the relationship between pressure and temperature for a specific refrigerant. Here’s how technicians can use PT charts to determine the saturated suction temperature:

1. Identify the Refrigerant: First, technicians need to identify the refrigerant used in the system. Each refrigerant has its own unique PT chart, so it’s crucial to ensure the correct chart is being used.

2. Find the Suction Pressure: Using the pressure gauge or manifold gauge set, technicians can determine the suction pressure of the refrigeration system. They can then locate this pressure value on the PT chart.

3. Read the Saturated Temperature: Once the suction pressure is identified on the PT chart, technicians can read the corresponding saturated temperature. This temperature indicates the point at which the refrigerant is fully vaporized and ready to enter the compressor.

By utilizing PT charts and accurately measuring the suction pressure, technicians can determine the saturated suction temperature with precision. This information is vital for maintaining the efficiency and performance of the refrigeration system.

In conclusion, the measurement and calculation of the saturated suction temperature are critical for ensuring the optimal operation of refrigeration systems. By using tools such as pressure gauges and digital thermometers, technicians can accurately measure the suction pressure and temperature. Additionally, PT charts provide a valuable reference for determining the saturated temperature based on the suction pressure. By incorporating these methods into their practices, technicians can effectively monitor and maintain the performance of refrigeration systems.

Vacuum Saturation Temperature

In refrigeration systems, the concept of vacuum saturation temperature plays a crucial role. Understanding this concept is essential for maintaining the efficiency and performance of the system. Let’s dive into an explanation of what vacuum saturation temperature is and its relevance in refrigeration systems.

Explanation and Relevance in Refrigeration Systems

The vacuum saturation temperature refers to the temperature at which a refrigerant becomes saturated and changes from a liquid to a vapor state. It is an important parameter used to calculate the performance of a refrigeration system, particularly in the suction line of the compressor.

When a refrigerant enters the evaporator coil of a refrigeration system, it absorbs heat from the surroundings and evaporates. As the refrigerant evaporates, its temperature rises until it reaches the vacuum saturation temperature. At this point, the refrigerant is fully saturated, meaning it has absorbed enough heat to completely vaporize.

The vacuum saturation temperature is crucial because it indicates the efficiency of the evaporator coil. If the suction temperature is too high, it may indicate that the evaporator coil is not absorbing enough heat from the surroundings. On the other hand, if the suction temperature is too low, it may indicate that the evaporator coil is absorbing too much heat, resulting in inefficient cooling.

By monitoring the vacuum saturation temperature, technicians can assess the performance of the evaporator coil and make necessary adjustments to optimize the system’s efficiency. It helps in maintaining the desired cooling capacity and preventing issues such as inadequate cooling or excessive energy consumption.

Moreover, the vacuum saturation temperature also affects the compressor’s operation. The compressor’s suction pressure is directly related to the saturation temperature. If the suction pressure is too high, it indicates that the compressor is working harder to compress the refrigerant. Conversely, if the suction pressure is too low, it may indicate that the compressor is not receiving enough refrigerant.

By monitoring and controlling the vacuum saturation temperature, technicians can ensure that the compressor operates within the desired range, maximizing its efficiency and lifespan. It also helps in preventing issues such as compressor overheating, which can lead to system breakdowns and costly repairs.

In summary, the vacuum saturation temperature is a critical parameter in refrigeration systems. It helps technicians assess the performance of the evaporator coil, optimize cooling efficiency, and ensure the compressor operates within the desired range. By monitoring this temperature, refrigeration systems can maintain their efficiency, prolong the lifespan of components, and provide reliable cooling.

Saturated Suction Temperature in Carrier Chiller

Application and Considerations in Carrier Chiller Systems

The saturated suction temperature plays a crucial role in the efficient operation of Carrier chiller systems. It is a key parameter that helps in determining the performance and reliability of the refrigeration system. In this section, we will explore the application and considerations of saturated suction temperature in Carrier chiller systems.

Importance of Saturated Suction Temperature

The saturated suction temperature refers to the temperature at which the refrigerant in the evaporator coil is completely vaporized. It is an essential parameter as it directly affects the efficiency and capacity of the chiller system. By maintaining the proper saturated suction temperature, the chiller can operate optimally, ensuring efficient heat transfer and cooling.

Calculating Saturated Suction Temperature

To calculate the saturated suction temperature, one needs to consider the refrigerant being used and the corresponding pressure at the suction side of the compressor. The pressure-temperature relationship of the refrigerant is crucial in determining the saturated suction temperature. By knowing the pressure, one can refer to the refrigerant’s pressure-temperature chart to find the corresponding temperature.

Indicating System Performance

The saturated suction temperature serves as an indicator of the system’s performance. If the saturated suction temperature is too high, it may indicate issues such as low refrigerant charge, insufficient airflow across the evaporator coil, or a dirty evaporator coil. On the other hand, if the saturated suction temperature is too low, it may suggest problems like overcharging of refrigerant or a restricted metering device.

Considerations for Optimal Performance

To ensure optimal performance of the Carrier chiller system, several considerations should be taken into account regarding the saturated suction temperature:

1. Refrigerant Selection: The choice of refrigerant can significantly impact the saturated suction temperature. Different refrigerants have varying pressure-temperature characteristics, which can affect the system’s overall performance.

2. Superheat and Subcooling: Proper superheat and subcooling levels are essential for maintaining the desired saturated suction temperature. Superheat refers to the temperature rise of the refrigerant vapor above its saturation temperature, while subcooling refers to the temperature drop of the refrigerant liquid below its saturation temperature.

3. Compressor Efficiency: The saturated suction temperature directly affects the compressor’s efficiency. Higher saturated suction temperatures can lead to reduced compressor efficiency, increased energy consumption, and potential compressor damage.

4. Heat Transfer: The saturated suction temperature affects the heat transfer process in the evaporator coil. By maintaining the correct saturated suction temperature, the chiller system can efficiently absorb heat from the cooling load.

5. Condensing Temperature: The saturated suction temperature is also related to the condensing temperature, which is the temperature at which the refrigerant rejects heat to the surroundings. Proper control of the condensing temperature is crucial for maintaining the desired saturated suction temperature.

In conclusion, the saturated suction temperature is a critical parameter in Carrier chiller systems. It helps in determining the system’s performance, efficiency, and reliability. By considering the application and various considerations mentioned above, one can ensure optimal operation and maximize the lifespan of the chiller system.

Saturated Suction Temperature in Ice Machines

The saturated suction temperature is a crucial factor that greatly impacts the performance of ice machines. By understanding its importance, we can optimize the efficiency and output of these machines. Let’s delve into the significance of saturated suction temperature and its impact on ice machine performance.

Importance and Impact on Ice Machine Performance

The saturated suction temperature refers to the temperature at which the refrigerant vaporizes in the evaporator coil of an ice machine. It plays a vital role in determining the overall efficiency and effectiveness of the refrigeration system.

When the refrigerant enters the evaporator coil, it undergoes a phase change from liquid to vapor. This process absorbs heat from the surrounding environment, causing the temperature to drop. The saturated suction temperature indicates the point at which the refrigerant is fully vaporized, ready to be compressed by the compressor.

Maintaining the correct saturated suction temperature is crucial for several reasons:

1. Optimal Heat Transfer: The saturated suction temperature directly affects the heat transfer process in the evaporator coil. If the temperature is too high, the refrigerant may not absorb enough heat from the surroundings, leading to inefficient cooling. On the other hand, if the temperature is too low, the refrigerant may become superheated, reducing the overall cooling capacity.

2. Compressor Efficiency: The compressor plays a vital role in the refrigeration cycle, and its efficiency is greatly influenced by the saturated suction temperature. If the temperature is too high, the compressor has to work harder to compress the refrigerant, resulting in increased energy consumption and reduced compressor lifespan. Conversely, if the temperature is too low, the compressor may experience liquid refrigerant floodback, leading to potential damage.

3. Ice Production: The saturated suction temperature directly affects the rate at which ice is produced in ice machines. By maintaining the optimal temperature, ice production can be maximized, ensuring a steady supply of ice for various applications, such as food service establishments, healthcare facilities, and more.

To determine the saturated suction temperature, it is essential to monitor the refrigerant pressure at the evaporator outlet. By using pressure-temperature charts or digital gauges, one can calculate the corresponding temperature. This information helps in adjusting the system parameters to achieve the desired saturated suction temperature.

In conclusion, the saturated suction temperature plays a critical role in ice machine performance. By maintaining the optimal temperature, we can enhance heat transfer efficiency, improve compressor performance, and maximize ice production. Understanding and monitoring this temperature is vital for ensuring the smooth operation and longevity of ice machines.
Conclusion

In conclusion, the saturated suction temperature is a crucial concept in the field of refrigeration and air conditioning. It refers to the temperature at which the refrigerant vaporizes completely in the evaporator coil. By maintaining the correct saturated suction temperature, technicians can ensure optimal performance and efficiency of the system. It is influenced by factors such as the refrigerant type, pressure, and superheat. Monitoring and controlling the saturated suction temperature is essential for preventing issues like compressor overheating, poor cooling capacity, and increased energy consumption. By understanding the significance of saturated suction temperature and its impact on system operation, technicians can make informed decisions to maintain and troubleshoot refrigeration and air conditioning systems effectively.

Frequently Asked Questions

What is saturated condensing temperature?

Saturated condensing temperature refers to the temperature at which the refrigerant in the condenser coil changes from a vapor to a saturated mixture of vapor and liquid.

What is saturated suction temperature?

Saturated suction temperature is the temperature at which the refrigerant in the evaporator coil changes from a saturated mixture of vapor and liquid to a vapor only.

What does low saturated suction temperature mean?

A low saturated suction temperature indicates that the refrigerant entering the compressor is colder than expected. This can be caused by issues such as low refrigerant charge, restricted airflow, or a malfunctioning expansion valve.

What causes high saturated suction temperature?

High saturated suction temperature can be caused by factors such as high refrigerant charge, restricted airflow, dirty evaporator coil, or a malfunctioning expansion valve.

How to calculate saturated suction temperature?

Saturated suction temperature can be calculated using the temperature-pressure relationship of the refrigerant. By knowing the saturated suction pressure, you can use a refrigerant pressure-temperature chart to determine the corresponding temperature.

How to measure saturated suction temperature?

Saturated suction temperature can be measured using a thermometer or a temperature probe placed at the suction line of the refrigeration system, near the evaporator coil.

What is superheat?

Superheat is the temperature difference between the actual temperature of the refrigerant vapor and its saturation temperature at a given pressure. It indicates the amount of heat added to the refrigerant vapor after it has fully evaporated.

What is subcooling?

Subcooling is the temperature difference between the actual temperature of the refrigerant liquid and its saturation temperature at a given pressure. It indicates the amount of heat removed from the refrigerant liquid after it has fully condensed.

What is compressor efficiency?

Compressor efficiency is a measure of how effectively a compressor converts electrical energy into mechanical energy to compress the refrigerant. It is typically expressed as a percentage and is influenced by factors such as compressor design, operating conditions, and refrigerant properties.

What is heat transfer?

Heat transfer is the process of transferring thermal energy between two objects or systems. In the context of refrigeration systems, heat transfer occurs between the refrigerant and the surrounding environment, such as the evaporator coil absorbing heat from the space being cooled and the condenser coil releasing heat to the outside environment.

What is condensing temperature?

Condensing temperature is the temperature at which the refrigerant in the condenser coil changes from a vapor to a liquid state. It is determined by the pressure at which the refrigerant is condensed and is influenced by factors such as ambient temperature and the efficiency of the condenser.

Control valves control the flow of fluid by reducing or increasing the cross section of the passage. This article discusses about how does a control valve work.

Control valves can stop, increase or decrease the discharge of the fluid. These valves find their applications in hydraulic as well as pneumatic systems. 

What is a control valve?

Control valves regulate the flow of fluid in the passage.

The applications may require different amount of discharge rate at different time. Valves are used to achieve this function.

How does a control valve control flow ?

The control valves regulate the pressure of the flowing fluid in order to change the discharge rates.

The cross section of the valve’s passage will reduce if one wants to reduce the flow rate and vice versa for increasing the flow rate.

Does a flow control valve reduce pressure?

In a high pressure system, the pressure can be reduced by using pressure reducing valves.

In pressure reducing valves, high pressure fluid enters the inlet and exits as low pressure fluid. It is done by restricting the flow downstream. Hence, we can say that a flow control valve can reduce pressure.

Which valve is best for flow control?

Many valves such as ball valves, globe valves, butterfly valves etc are used in industries out of which a globe valve is considered the best.

Globe valves are good at regulating the flow. They are used for throttling purposes. The opening and closing time of a globe valve is much shorter than other valves which makes this valve more desirable.

Can a control valve increase pressure?

Higher the flow rate through the valve, higher will be the pressure drop and vice versa.

While the pressure reduces downstream in pressure reducing valves, the pressure increases upstream.

Can ball valve be used for flow control?

Globe valves are the best type of valves for regulating the flow. Although ball valves can also be used to serve this purpose.

Opening and closing of ball in ball valve controls the flow. Ball is the main characteristic of ball valve. It can be closed, open or partially closed. Ball valves have an advantage over others because it is easier to tell whether ball valve is open or closed.

How do you choose a control valve?

A lot of characteristics are taken into account for choosing a control valve. Some considerations are noise, maintenance, cost and energy consumption. A good valve should serve most of the following-

• Ability to regulate the rate of flow or throttle.
• It should work with low turbulence.
• Short opening and closing time as it can be used in emergency.
• Tight seal that prevents leaks.
• Opening at a pre set pressure.
• It should be able to hold any corrosive materials to avoid rapid wearing.

What is a pressure regulator?

The type of valve that is used for controlling the pressure of the fluid to a desired value is called as pressure regulator.

Pressure is controlled by using a negative feedback from the controlled pressure. If the flow rate is high inside the valve then pressure drop will also be higher.

What are the types of pressure regulators?

There are mainly two types of pressure regulators used in industry. They are-

• Pressure reducing regulator– As the name suggests, it is a valve that reduces input pressure to a desired one at the output. It is a open valve that is installed in upstream.
• Pressure sustaining regulator– Unlike pressure reducing regulator, the pressure sustaining regulator maintains a set pressure at the input side by opening itself to allow the flow when it exceeds the set value.

How does a flow control valve affect pressure?

Generally, by controlling the pressure of fluid the flow of fluid can be controlled.

A higher flow rate through a restriction will result in greater pressure drop and similarly a lower flow rate will result in lower pressure drop. The pressure will be high upstream as the downstream pressure reduces.

What type of control is used to regulate the pressure of water?

Pressure of water can be regulated with the use of a certain type of valve. That valve is called as a water pressure regulator. It is also called as pressure-reducing valve.

It is a specialized plumbing valve which reduces the pressure coming into inlet. It is not needed everywhere but if the pressure of water from municipal corporation is high then a water regulator must be used in order to reduce the pressure.

How does a water pressure regulator work?

A water pressure regulator will look like a dome shaped device that would be situated near the mai shut off valve where the main water line enters the house.

It has a spring loaded mechanism for regulating the pressure of the water. A diaphragm is attahced at the end of spring which widens and narrows depending upon the amount of water coming inside the valve.

A water pressure regulator protects the inner valves of appliances as there will be less stress on them.

Mathematically,

F = P_i – P_o + P_oS + f

Where,

F is diaphragm spring force

f is poppet spring force

Pi is inlet pressure

Po is outlet pressure

s is poppet area

S is diaphragm area

What are the different types of pressure reducing regulators?

The pressure reducing regulators can be classified on the basis of number of stages through which water is passing. They are-

• Single stage regulator– As the name suggests, the water passes through a single stage. When operating with this type of valve, the outlet pressure starts climbing when the supply pressure gets low.
• Double stage regulator– In this type of regulator, the water passes through two stages. The first stage has a pre set value of pressure, so the inlet pressure gets converted to this pre set value. The next stage is variable that is user can control the pressure of the fluid by knob. This way the user can achieve the desired pressure just by rotating the knob.

The pressure gauges on the regulators show the magnitude of pressure of flowing fluid.

Installation tips on water pressure regulator

The best location of installing a water regulator is beside the main shutoff valve controlling the water coming into inlet.

This location is desirable because it makes it easy to quickly shut off the control valve and allows the regulator to protect all the pipes present in the system.

If the regulator needs to be replaced then it is easier to replace it with the same brand and model because it will have the examct dimensions as the previous one.

Maintenance of water pressure regulator

Like every mechanical component needs maintenance after some point of time, water pressure regulators also need maitenance for their smooth operation.

If water hammering takes place or other inconsistencies take place then it is a sign or symptom that pressure regulator is not working properly. It is always recommended to test the regulator at least once a year or whenever there is a slight noticeable change in regulator’s effectiveness. If the adjustment screw’s movement has no effect in changing the pressure then it can be concluded that it should be replaced.

Too much water pressure in the system can cause water hammer to occur in walls or sometimes burst pipes of the system.

What are the factors to consider when selecting a control valve?

Many factors are considered while selecting a control valve. If not considered, the system may work inefficiently. The major considerations are-

• A valve should have a good throttlability and should be able to control the rate of flow.
• The operation should not be turbulent.
• The valve should have a shorter opening and closing time.
• The valve should be able to tighten properly to avoid leaks through the system.
• It should be able to open at a pre set pressure.
• It should be able to handle abrasive fluids.

What are the three types of control valves used in hydraulic systems?

Hydraulic systems can be broadly classified into three types. These three types are- flow control valves, pressure control valves and directional control valves.

• Directional control valves-Directional control valves can start, stop or change the flow of direction of the flowing fluid. Most commonly used directional valves include directional poppet valves, directional spool valves and check and non return valves.
• Pressure control valves-Pressure control valve use throttling to regulate the flow of fluid. They switch at pre determined pressure setting. Examples of pressure control valves are pressure valves relief function, pressure valves fixed function, pressure valve reducing functions etc.
• Flow controlled valves-Flow control valves increase or decrease the area of throttling point to control the flow of fluid. Examples of flow controlled valves are pressure compensated valves, throttle valves etc.

What is CV value of control valve?

CV value of a control valve or Value flow co efficient of a control valve is defined as the ratio of capability of flow of a control at fully open conditions to the pressure drop taking place through the valve.

This particular value is significant as it is the only standardized selection method for control valve sizing which is why it is used throughout the industry.

Mathematically,

Where,

Q is the flow in gallons per minute

G is the specific gravity of fluid

Del P is differential pressure over valve.

Valve Positioner is one of the most extensively used control valve accessories in different industries.

To regulate the rate of gas and liquid flow, a large number of valves are used in oil and chemical plants as well as food, pharmaceutical, steel plants. Each valve is associated with a positioner that controls the valve’s position according to the command from the control system.

What is a Valve Positioner?

Valve Positioner is a device installed with a control valve to get precise and rapid control over flow, to reduce frictional effect and steady valve position even with fluctuating pressure.

Valve Positioner, Image Source: cascadeautomation

The use of a Valve Positioner with a control valve is essential to get accurate and quick control without any hysteresis. The controller sends a direct input signal to the Positioner instead of the actuator. The control signal applied to the Positioner operates the actuator stem through a flapper nozzle mechanism.

Valve Positioner, Image Source: chemicalengineeringworld

Valves are a vital part of any industry that is installed on pipes to control the flow rate of gases and liquids. Hundreds and thousands of valves are required as per the capacity of a plant. Proper control of opening and closing and adjustment of degree of opening of these valves is essential. To get the correct stem or shaft position as set by the control system, Valve Positioners are used widely so that depending on the input from the controller, it can adjust the air pressure to the actuator diaphragm to maintain the correct stem position of the valve.

Where is a Valve Positioner located?

Valve positioners are installed with a control valve to regulate the position of a valve depending on the predecided data for a process variable which may be flow, pressure, or temperature.

As per the type of Valve actuator, the position of Valve Positioner is determined. Normally, the location of a Positioner in case of pneumatic type actuator for a linear control valve is yolk or top casing. In a rotary control valve, the Positioner is located close to the end of the shaft.

Whether rotary or linear, in either types of control valve, the positioner sits and travels along with the valve stem. It measures the distance travel in case of linear valve and degree of rotation for rotary valves and controls the valve as per the points set by the controller.

Location Of a valve Positioner, Image Source: instrumentationtools

What is the necessity of a Valve Positioner?

Valve Positioner helps a control valve to respond quickly as per the changes of the process variable. They are advantageous for a system where fluctuations are the main obstacles to efficiency and quality.

The necessities of a Valve Positioner are explained below:

• Speed: Valve Positioner minimizes the response time of the system, whether operating above or below the set point
• Accuracy: A Positioner gives better resolution and more precision than an actuator can provide on its own. Controller send input signal directly to Valve Positioner. The feedback mechanism provided in the positioner allows to cross-check the valve position and readjust air requirement/pressure to reposition the stem as per the signal provided by the controller. Reduction in friction: Reduces friction effect of valve stem packing, especially beneficial for high-temperature packing material like graphite.
• Range: Valve Positioners also help to control a wide throttling range.
• Split Ranging: Using a Valve Positioner, we can use two valves with one controller(4-12 mA and 12-20mA) without any error.
• Seating friction: Help to defeat seating friction in case of a rotary valve.
• Increased flexibility: By using a Valve Positioner actuator is enable to face high apparatus air supply pressure.
• Flexible configuration: Utilization of a Positioner removes the limitation on distance between the controller and the control valve as the control signal can be sent electronically and converted to pneumatic signal at the input point of the Positioner. On the other hand if an actuator is operated pneumatically over long distance, the control becomes erratic.

Valve Positioner types

A Valve Positioner can receive or transmit both electrical as well as pneumatic signal. The classification of Valve Positioner is based on type of signal it can receive and transmit or a combination of both. 

Different types of Valve Positioners are:

• Pneumatic Valve Positioner:  This type of Positioner get pneumatic signal from controller and they also transmit pneumatic signal to the actuator. They provide a high air pressure to change the position of the actuator and are quite safe for use.
• Electric valve positioners: They transmit and accept electrical signals.
• Electro-pneumatic valve positioners: Also known as “Analog Positioner” because the electrical input received are in the form of analog signals. An electrical signal is fed from the controller but in return Positioner deliver a corresponding pneumatic signal to the pneumatic valve actuator.
• Digital or “smart” valve positioners: Popularly known as “Smart Valve Positioners.” This type of Positioner uses a microprocessor to control the valve actuator and record and monitor data. The electrical input is in the form of a digital signal, and the corresponding output is a pneumatic signal.

Valve Positioner working principle

A pneumatic Valve Positioner is a mechanical device employed to fine-tune the movement of the stem of a control valve.

The pneumatic Positioner is provided with a feedback mechanism to accurately identify the control valve stem position and compares it with the input signal. Based on the feedback signal, the positioner varies the supply of air to the actuator stem in order to bring the stem into the position dictated by the signal sent to the Positioner from the controller. 

There are two philosophies on how a positioner is implemented. One is where the air is used to opena valve stem, and the other is when to air the used to close a valve stem. The description of the mechanism noted below is for the second case, i.e., the air is used for closing a valve stem. This is also called a direct-acting Valve Positioner.

Direct Acting Valve Positioner, Image Credit: instrumentationtools

The Positioner is normally fitted into the yolk or pillars of the actuator. It is operated by an input air pressure of 3-15 psi (0.2 bar to 1.1 bar); as the signal is provided from the controller to open the valve stem, the input air pressure to the input instrument increases. The input pressure acts on the input signal diaphragm, which drives the diaphragm along with the flapper connecting stem. The flapper connecting stem opens the supply flapper allowing the supply air to act on the actuator stem diaphragm.

During this time, the exhaust flapper is in the closed position as the flapper connecting stem is deflected to the right. As the air pressure is increased, it forces the valve stem down. As shown in the figure above, the positioner lever moves clockwise as the valve stem goes down.

Due to this clockwise rotation of positioner lever, range spring experiences a compression through cam. As soon as the valve stem reaches the position as per the set point provided by the controller the range spring exerts a balancing force closing both the exhaust and supply flapper and the desired control action is achieved.

On the other hand, if the controller sends a signal to open the valve, the signal pressure decreases. With the decrease in signal pressure, the force from the range spring push the flapper linking stem towards left direction. As a result, the exhaust flapper is opened. The force acting on the actuator diaphragm also decreases causing a upward movement of the valve stem until an equilibrium in force balance is achieved.

The device used for regulating the flow of fluids in passage ways are called as valves. This article tells us about what are valves uses and related insights.

• Gate valves
• Globe valves
• Butterfly valves
• Ball valves
• Check valves

Application of valve in industry

Industries use many types of valves which include gate valves, ball valves, globe valves, butterfly valves and check valves. 

The applications of above mentioned valves are given below-

• Gate valves– They are used in high temperature and pressure conditions. They are used for binary operations such as ON/OFF. They can be used in both directions inside a flow circuit. They operate on low friction and can be used both ways.

• Globe valves– They are generally used for throttling purposes. These valves are used as stop check valves as their opening and closing time is much shorter than other valves. The body ring seating surface is easier in globe valves.

• Ball valves– These valves are used to regulate the flow of corrosive fluids and slurry and are also used in oil industry. They provide leak proof service.  They are compact and requires little or no lubrication.

• Butterfly valves– These valves are used in pharmaceutical, chemical and food processing services. They are used for low pressure and low temperature applications. They can be installed without pipe dislocation. They are very reliable and require little or low maintenance.

• Check valves– They are used in waste water management and in industries such as refining, petrochemical, chemical, viscous fluids etc. These valves prevent backflow and serve as backup system. They sustain high pressure which helps in preventing the backflow.

What is a valve?

As mentioned above, valve is a device that is used for regulating or controlling the flow of fluids by opening or closing passage ways.

By opening or closing passage ways, valves create obstruction (or remove obstruction) from the fluid flow which enables the flow to stop or continue (if it was being stopped initially). The amount of closing and opening can control the speed and discharge of the flow.

Image credits: Paul Goyette, Water valves with spigots, CC BY-SA 2.0

Working mechanism of a simple valve

Valves can be used to regulate or control the flow of fluid. That means it can start/stop the flow as well as control the discharge of the flow as well.

If a valve wants to stop the flow, it will simply close the entire cross section of the passage. To control the discharge, it will partially close the cross section so the flow will occur only through a small portion of the passage.

Variation of sizes in valves

Depending upon the application, valves can vary in size.

The size of a valve is typically in the range of 0.1mm to 60cm. Although there are special valves which have diameters exceeding 5m. They can be cheap (simple disposable valves) and of very high cost that are used for special purposes.

Types of valves

Valves can be classified on many basis. To make it simple, we classify them on the basis of their mode of actuation.

Different types of valves used in industries are-

• Hydraulic– Hydraulic valves are used to control the fluid flow in a hydraulic circuit. This is done by controlling pressure and flow rate of flowing fluid and are actuated by action of a hydraulic fluid.
• Pneumatic- Pneumatic valves are used to control or regulate the flow of air or any other inert gas. These valves are actuated with the help of pressurized gas.  
• Manual– Manual valves are simply those valves which needs to be actuated by a manual operator.
• Solenoid valve– These are control units which disrupts the flow of fluid when energized or de-energized.
• Motor valve- Motors are used to actuate the valve. These are used in pumps.

Components of valve

A simple valve comprises of two main parts- Body and bonnet. Both of them form a casing that is responsible for holding the fluid that goes through the valve.

• Body-As the name suggests, body is the outer casing of the entire valve that contains internal parts.
• Bonnet-Bonnet is the covering of the valve. It may be semi-permanently screwed to the valve body or simply bolted onto it. Stem passes through bonnet that acts as seal of the valve.
• Ports-These are small passages that allows the fluid to pass through the valve.
• Handle or actuator-It is used to control the action of valve manually. With the help of this, the valve can be closed or open as and when needed. The movement of actuator can be automated by the use of sensors and electric circuit.
• Disc-It is an internal part in the valve assembly which adjustably obstructs the flow of the fluid inside the valve.
• Seat-It is the inside surface of the body that comes into contact with disc to make a leak-tight seal.
• Stem-It is responsible for transferring motion from the handle to disc.
• Valve balls-These are used for high pressure and heavy duty applications. They are generally made of Titanium and stainless steel and sometimes plastics such as ABS, PVC or PVDF.
• Spring-Some valves have spring for spring loading to set the position of disc and reposition it as and when needed.

What is trim in valve?

Trim simply refers to the internal parts of the valve assembly or internal elements of valve.  

According to API standards, trim contains disc, stem, valve balls, spring, seating surface in the body gate, gate seating surface, bushing, stem hold guide and small internal parts that contact the service fluid.

What valve operating positions of valves?

Valve operating positions are the operating conditions based on the position of disc inside the valve.

• Two port valves– For two port valves, the operating positions can be completely shut or completely open and sometimes partially open to precisely control the degree of flow.
• Three port valves– These kind of valves serve many functions. Some of them are used as shuttle valves, thermostatic valves, single handler mixer valves etc.
• Four port valves- It has four equally spaced ports round the body. It can be operated in two positions. This kind of valve is used to simultaneously isolate and bypass a sampling cylinder that is installed on a pressure line.

Limit Switch valves have wide use in our daily life at home as well as in our workplace.

A simple example of the application of Limit Switch is the light comes on inside the fridge whenever we open the fridge door. Here Limit Switch detects if the fridge door is opened or closed.

Another most frequently seen use of Limit Switch is in the overhead shop and garage doors where Limit Switch stops the movement of the door at its fully opened position.

What is a Limit Switch valve?

In an automatically operated machine, Limit Switches are used to convert the mechanical movement of the device into an electrical signal.

As per its name ‘Limit,’ these switches mainly define the limit or boundary of travel of an object or machinery. At the same time, these electromechanical devices indicate the presence or absence of an object.

After getting physical indications, it is easy to operate the whole circuit by converting mechanical motion into an electrical signal.

Limit Switch, Image Source: Automation forum

What is the function of Limit Switch?

Limit Switches are activated by the presence or absence of an object or by the movement of machinery.

The primary function of a Limit Switch is to open or close a contact in a circuit when a certain distance covered by a motor-operated device has been reached. Limit Switch is applied in the control circuit for different purposes like slow down, reverse, or stopping the operation of the machinery.

A Limit Switch consists of an actuator connected to an electrical switch. As soon as a moving machine or a moving machine part strikes the actuator, the operation of the Limit Switch begins and actuates the switch. As a result, the Electrical circuit controls the machine and its motion.

Limit Switches can be used either as a control device for standard operations or as emergency switches to stop the inappropriate functioning of the machine.

Components of a Limit Switch

A Limit Switch is a detection kind of switch inside a metal or resin casing. The outer case is necessary to protect the switch from dust, dirt, external forces, moisture, oil, etc.

The main components of Limit Switch are:

• Actuator: This is the part that comes in physical contact with the moving machine or machine part. It is constructed with tough material to withstand a significant amount of force and shock.
• Operating head: Sometimes, the actuator is connected with an operating head which converts the rotary, linear, or perpendicular motion of the device into an electrical signal to operate the switch.
• Switch body: It refers to the whole electrical contact mechanism.
• A series of Electrical terminals: Screws or screw/clamp assembly essential for wiring purposes.

Components of a Limit Switch, Image Source: @pub/@electrical

What triggers a Limit Switch?

Limit switches are triggered by a physical force applied to the actuator of the switch by machinery. The cams connected to the actuator shaft readily activate the switch.

When the product comes to physical contact with the actuator of a Limit Switch, this physical touch is converted into an electrical signal which activates or deactivates the electrical circuit within the switch. As the product moves away, the actuator and the switch go back to the normal position.

Different types of actuators are used in Limit Switches depending on different applications. Actuators are mainly selected considering certain factors like travel distance, shape, speed, the direction of the machine part being used to trip the Limit Switch. The main types of actuators are flexible rod, plunger, and roller lever.

Function of a Limit Switch, Image Source: omron.com

What is a valve position switch?

Valve position switches are electrical switching devices associated with a Limit Switch for giving an easy visual indication of the current position of the valve assembly.

Valve position switches inform us about the position(open, closed or in an intermediate state) of the valve in the form of continuous signal. These switches can be fixed directly on the actuator of the valve. They can be used in combination with a valve positioner.

Limit switches are activated by the physical touch experienced by the actuator of machinery. The mechanical motion experienced by the actuator plunger is converted into electrical signals which in turn change or regulate the make or break state of the circuit.

Valve position switch, Image credit : aoxactuator.com

How does a Rotary Limit switch work?

Rotary Limit Switches are generally used to control shaft revolutions or to limit movement based on the rotation angle of industrial machinery.

A Rotary Limit Switch is an assembly of gears and cams to trigger a microswitch when the preset number of revolutions has been reached. Here the working principle of a worm drive has been followed. Gears are linked to a cam mechanism that rotates entirely depending on the central gear.

In a Rotary Limit Switch, a shaft must turn a predetermined number of revolutions before the contact changes state as in cranes.

Rotary Limit Switch consists of a shaft that is connected to the shaft of a gear box through a coupling. When the shaft of the gear box rotates, the shaft of the Rotary Limit Switch also rotates. Cams are mounted concentrically with the gears, so as the gears turn, the cams rotate, and rocker arms attached to the cam lobes trip switches at set positions.

Rotary Limit Switch, Image Source: Motion control tips

Generally the input gear is a worm gear but planetary and spur gear are also used. Gear type is decided depending on the requisite gear ratio. The limit at which the switches are activated depends on design of cam lobes and on the ratio of the input gear.

Rotary Limit Switch, Image Source: ohmic-local-manufacture

At least two cams and two switches are essential for a Rotary limit Switch assembly, one for each end or upper and lower limit of travel of the machinery.

Frequently Asked Questions (FAQs)

Q.What are the applications of a Limit Switch?

Ans: Though Limit Switches are available in many forms and perform different functions but in general they are electromechanical switches which are operated by the presence or motion of an object.

Some applications of Limit Switches are as follows:

• In material handling application giving indication of passage of material from one platform to another.
• Widely used in overhead cranes
• Used in automatic machinery.
• Used in High speed equipment.
• Also used in machine tools and rusticate the travel of a machine axis.
• Used to control the liquid level in pumping system.
• Used in elevators and conveyors.

Q. What are the types of Limit Switches?

Ans: Limit switches are classified based on motion of the lever and type of actuating mechanism.

Limit switches are classified based on the actuating mechanism as:- Lever type and Plunger type. Based on the type of motion the limit switches are classified as Rotary motion type and Linear motion type.

Lever Type: A switch with lever type actuating mechanism has a lever attached to it. When the moving machinery or equipment comes in contact with the lever it pushes the lever, which in turns connects or disconnects the electrical circuit. The contact point of the lever with the machinery is normally provided with a roller. The lever is also provided with a retrace mechanism to bring back the lever to original position once the machinery/ equipment is removed from the position. It normally finds use in lifting cranes, lifts etc.

Plunger Type: A Push or plunger type Limit switch on the other hand, gets actuated when the machinery or equipment presses against the push button provided in the limit switch. This is the most common type of limit switch which are available in a car or a refrigerator door. A typical push type limit switch is shown below.

Rotary Motion Limit Switch: A rotary motion limit switch is normally attached to a rotating device such as an electric motor. It detects the rotary motion of the shaft or device connected to it. On achieving specified number of rotations or in other cases angles set for rotation, the limit switch gets activated. They are normally used for rotating service such as crane hoisting or in service where linear motion is translated to rotating motion.

Linear Motion Limit Switch: The most common type of limit switch used in the industrial application is the linear motion limit switch. They detect the linear motion of the equipment or machinery and find wide sue in packaging, manufacturing, motor control and other consumer applications.