Sangeeta Das

In this article we will discuss different facts related to Low Limit Switch. As the name indicates Low Limit Switch is used for control applications.

Low Limit Switch is most widely used in the equipments where low temperature protection is a prior requirement. Low Limit Switch(also known as Freeze Stats)is designed with a vapour charged capillary sensing tube.

Mainly used in refrigerated cells and different equipments where operational temperature is maintained very low, minimum operational temperature is up to -40°C.

What is Low Limit Switch?

The Low Limit Switch plays the role of frost protection switch in water treatment and water supply plants, HVAC air conditioning( preferred in cold areas) etc.

Low Limit Switch is designed to monitor low temperature and to prevent damages that may occur due to frost accumulation. Generally suitable for hot water coil pipe unit, cold water pipe unit, heat exchanger, liquid carrying pipelines, surface air cooler etc.

Certain features of Low Limit Switch which make it more versatile for its wide range of application are easy to read dial, compact size, high reliability, quick response action etc.

Low Limit Switch Working Principle

The working principle of Low Limit Switch is single- pole double-throw.

Low Limit Switch consists of a long copper capillary tube, full of vapour inside and acts as a sensing part. If any part of the capillary has senses a temperature lower than the setup point, inner switch will be off until temperature rises upto 2 or 2.5 °C than the set temperature. After that again the switch starts working.

To detect the low temperature and protective action the capillary tube is enclosed inside the pipeline. The long sensing tube contains vapour and the main body has an adjustable enclosure.

Generally freeze stats are made of 1/8”OD flexible tubing, filled with temperature sensitive gas vapour, the pressure of gas vapour goes down with decreasing temperature. The capillary tube is connected to a control box, where a temperature is set(35 F typically).

If any part of the temperature sensor element experiences a temperature drop lower than the predetermined or set point, the freeze stat will immediately trip. The sensor element has different lengths up to of 20 ft long and generally trip occur if the length within 12” to 18” goes lower than the set point.

Low Limit Switch were designed for use on HVAC equipment which require low temperature cut out protection to prevent cooling coils from freezing. Low Limit Switch is connected between the heating and cooling coils on the supply side of the fan unit and gives an indication of lower temperature as per the senses received by the sensing element.

Low Limit Switch or Freeze Stats has both automatic and manual reset versions with a wide range of capillary lengths.

Applications of Low Limit Switch

Low Limit Switch protects cooling coils in air handler systems by preventing frost build up.

Low Limit Switch are most widely used in HVAC equipments, cooling coils and heat exchangers.

 The thermostat and capillary sensing element provide an antifreeze function by sensing the lowest temperature along any one foot section of capillary tube. Automatic reset relays signal the building management system and also cut off the fan. As the temperature goes below the fixed safety point(set point), the low limit Switch immediately detects it.

Low Voltage Limit Switch

Low Voltage Limit Switch is used to control loads such as blower fans and heating elements without an intervening relay.

Low Voltage Switch is connected in circuits where a low voltage has to be maintained for perfect running of the machine. In case of a magnetic relay circuit it is so connected that a drop in voltage cause the motor starter to disconnect the motor from the line.

Limit Switches are used in a wide range of application including the production floor as well as daily lives. Limit Switches are the mechanical/electronic components on a production floor for control and safety purposes. Although the function of a Limit Switch is very obvious, wide variety of these switches are available in the market to offer flexibility.

Low Temperature Limit Switch

Low Temperature Limit Switch is a special version of limit switches designing for low operational  temperature applications  such as refrigerated cells or equipments.

Temperature Limit Switch controls the electrical circuit which in turn regulates the machine and its moving parts as per the requirement. Special materials are used to manufacture Low Temperature Limit Switches and it can perform well at an operational temperature below down to -40°C.

Low Temperature Limit Switch acts as a pilot device in magnetic starter control circuits and allow it to regulate the start, stop, slow down or accelerate the functions of an electric motor.

Some of the manufacturer design certain Low Limit Switches that can be used in the most hazardous and arduous application of industries to withstand harshet conditions and duty cycles including extreme cold at -60 °C.

How to Test a Low Limit Switch?

With the help of a basic Ohmmeter or Digital Multi-meter we can know whether the Limit Switch is working or not.

To test a Limit Switch we have to follow the following steps:

1. first disconnect the switch from the system and then place the Digital Muliti-meter leads to each terminal.
2. The resistance should be very high for a normally open(NO)limit switch.
3. If the Limit Switch is normally closed(NC), the resistance should be closed to zero.
4. Now keeping the limit switch into active position, measure the resistance.
5. It should be the opposite in this setting, if there is no transition, the limit switch is bad.

Installation of a Low Limit Switch

The steps followed for installation of a Low Limit Switch are as follows:

• To install on a wall, make a hole with the help of a drilling machine as per the instructions in the manual and then lock the switch using self-tapping screw.
• Set the temperature in such a manner that environmental temperature should not be less than the setting temperature. Environmental temperature shouldn’t be lower than setting temperature.  Keep away from cold and hot sources and avoid installing in outdoor.
•  Never press the sensing capillary to avoid change in calibration result to maintain accuracy.
• For ensure accurate and reliable action, should at least wrap over 200mm length sensing capillary onto pipeline of related protection devices.
• In case of heat exchanger and surface air cooler, the sensing capillary of the limit switch should be installed at their leeward side.
• Make sure that power should be OFF before staring wiring to avoid any kind of accident.

In this article we will discuss about Radioactive Waste Examples which are quite hazardous.Radioactive waste are the by product from different activities  like nuclear research, nuclear power plants, defence sectors, earth mining, hospitals etc.

Examples of Radioactive waste are listed below:

• Wastes from Defence Activities
• Mill Tailings
• Transuranic waste
• Electricity Generation
• Nuclear fuel cycle
• Reprocessing of used fuel
• Mining through to fuel fabrication
• Decommissioning and dismantling of nuclear reactors
• Waste from Nuclear Conflicts
• Natural nuclear waste sources
• Waste from Medical purposes

Radioactive waste mainly contains radioactive materials due to which the disposable and storage of these waste is an important matter of concern.

Production of radioactive waste should be avoided as much as possible. If the production of radioactive waste is unavoidable, then try to minimise the production rate.

What is a Radioactive Waste?

Radioactive waste should be always managed with care and following the restrictions as per the Government rules throughout its life cycle starting from arising to recognised end point.

Once the radioactive waste has been generated, its influence does not end until it is decayed naturally. Packaging of radioactive waste in containers doesn’t reduce their radioactivity and radioactivity reduction by dilution is an expensive option.

Most of the industries produce radioactive waste in large amount and these wastes should be disposed safely to avoid the spread of contamination. 

Radioactive Waste Examples in Details

Radioactive waste is considered as a serious threat to mankind as well as nature because of its long duration for decantation.

Wastes from Defence Activities

Radioactive waste produced from defence activities are similar to wastes produced from nuclear power plants, but the amount of waste produced is much less if we compare it with total amount of waste production. The sources of production are activities like Navy operations, decommissioning of nuclear powered submarines, clean up of disused military sites etc.

Mill Tailings

They are the by product during the milling process of certain ores to get uranium or thorium. Mill Tailings  consist of thorium, radium and small residual amount of uranium. Mill tailings are not highly radioactive due to the less amount of radioactive materilas but possess long half lives.

Transuranic waste

These type of waste are contaminated with alpha-emitting transuranic  radionuclides and have a half lives more than 20 years, but they are not classified as HLW. More caution is required for its disposable  than LLW and ILW due to the longer half live. Transuranic waste, sometimes called TRU are obtained generally from the manufacturing process of nuclear weapons.

Electricity Generation

Use of nuclear reactors to generate electricity is a major source of radioactive waste, which can be classified as HLW. The reactor operation results highly reactive fission products, uranium and plutonium produce transuranic elements which mix with used fuel.

Nuclear fuel cycle

The whole cycle of nuclear fuel starting from radioactive fuel extraction, processing, uses and finally disposal generate radioactive wastes. If the disposal process is not proper enough then the rate of waste production is quite high.

Reprocessing of used fuel

Used fuel also possess radioactivity because they still contain some amount of U-235,different plutonium isotopes, U-238, the amount can be resemble with 96% of original uranium content and almost half of the original energy content. These used nuclear fuel has been reprocessed to extract fissile materials and also to reduce the volume of HLW.

Mining through to fuel fabrication

Fine sandy tailings are generated from the uranium mining operation and these tailings contain all the radioactive elements which are available in uranium ore.  Generally tailings are kept under water in dams and after few months covered with a layer of clay and rock to prevent the leakage of radon gas.

Decommissioning and dismantling of nuclear reactors

Decommissioning and dismantling of nuclear reactorsand other nuclear facilities are also responsible for radioactive waste generation.

Waste from Nuclear Conflicts

Nuclear conflicts among different countries is a source of radioactive wastes on a large scale. In this case, due to the use of nuclear arms a vast area may be contaminated by radioactive materials and the effect of contamination in the soil remains for a quite long period of time which is really hazardous for human being, animal and for the whole atmosphere.

Natural nuclear waste sources

Crude oil, natural gas, coal etc are nuclear materials available in our nature. These radioactive materials generate radioactive waste during the industrial processes to extract them for commercial purposes. Coal power plants, oil refineries and drilling plants, gas industries produce radioactive by products like radium, radon etc.

Waste from Medical purposes

Medical  is one of the main sources of radioactive wastes, medical research for medicines and different medication facilities generate huge amount of radioactive wastes. For example, during  the surgery of  thyroid cancer, lymphoma, bone cancer etc radioactive wastes are produced. 

Classification of Radioactive Waste

Radioactive wastes are classified depending on the amount of radioactivity present and the heat produced by this radioactivity.

Radioactive waste are classified as below:

• High Level Waste (HLW): Majority of radioactivity is associated with HLW, temperature may rise significantly due to their radioactivity, the storage and disposal of these wastes should be well planned. When the production of electricity has been completed, a huge amount of HLW is remaining in the form of  spent fuel inside the reactors. These are highly radioactive and emits heat, HLW always require cooling and shielding for disposal.  
• Low Level Waste(LLW):Generally produced from reactor operations, medical, academic, factories and other commercial activities where radioactive materials are used. LLW are contaminated with radioactive materials and sometimes become radioactive through exposure to neutron radiation. Some LLW are wiping rags, mops, tools, papers, filters, clothing, medical tubes, injection needles which have small amount of short lived radioactivity. LLW may be stored on site by licensees until has been decayed away or disposed as common trash.
• Intermediate Level Waste(ILW):They contain higher amount of radioactivity and need some shielding, more radioactive than LLW. But heat generation is less than 2 KW/m³, so design or selection for storage and disposal is not considered much. Contaminated materials from reactor decommissioning, chemical sludge, resins, metal fuel cladding etc typically considered as ILW.

• Very Low Level Waste(VLLW):Amount of radioactive materials present in VLLW is not considered as harmful to people or surrounding environment. Examples of VLLW are demolished materials like concrete, plaster, bricks, metal rods, pipes, valves etc obtained during dismantling works on nuclear industrial sites. Food Processing, chemical, steel industries also produce VLLW, as small amount of radioactivity present in certain minerals used in their manufacturing processes.

Effects of Radioactive Waste

Major effects of Nuclear Waste are as follows:

• Though great care is maintained for the transportation of radioactive waste, sometimes leakage or accident may occur. The leakage of radioactive waste during transportation will lead to soil contamination and make it unusable for cultivation, the effect remains for a long period of time because many of them have a long half lives. 
• Radioactive waste can cause serious diseases for human being as well as animals which may lead to even death. In a long term it can change the DNA structure and alter the future generations.
• The area which is used for storage purpose is fully polluted and becomes useless for any other activities.
• Radioactive waste has a significant adverse effect on nature.
• A significant effect can be observed in nature including plants and animals which in turn influence the human life through the food chain.

To know about Limit Switch Valve( Click here)

In this article we will discuss about the High Limit Switch Furnace. To operate a residential gas furnace safely and efficiently the use of a High Limit Switch is essential.

High Limit Switch, also known a “Fan Limit Switch” or simply “Limit Switch” plays an important role from safety point of view. The main function of a Limit Switch is to sense the temperature in the air plenum of the gas furnace and shuts off the burner as temperature goes to a limit which may cause a dangerous or uncomfortable condition. 

Why Does High Limit Switch Trip?

The suspected reason for High Limit Switch tripping is lack of airflow through the furnace, due to which temperature becomes high and the Limit Switch trips off.

An airflow issue through the furnace generally leads to Limit Switch tripping. Lots of reasons are there which prevent an adequate airflow throughout the system.

• Air Filter: A dirty filter is one of the most common issue which prevents the flow of air through the furnace, resulting a very hot heat exchanger causing tripping of the Limit Switch. On the body of the air filter certain arrows are marked for the direction of air flow, these arrows must be followed properly to avoid any kind of air blockage.
• Blocked Register: Through the registers, air flows out of a furnace, therefore the register should not be blocked to ensure proper movement of air.
• Exhaust Vent: After the burning of gases inside the furnace, the exhaust gases should be vented out. The blockage of exhaust vent may cause overheating.
• Blower Motor: If the blower motor is not working efficiently and air flow is not fast enough, then the heat exchanger get overheated.
• Blocked ‘A’ Coil : ‘A’ Coil used to flow air from the system is sometimes clogged with debris.
• Defective Limit Switch: Sometimes the Limit Switch itself going bad, this may be another reason for tripping. Then it has to be replaced or repaired for proper and safe functioning of the furnace.

Open High Limit Switch Furnace

A Furnace High Limit Switch is designed in such a manner so that it can activate and deactivate the furnace blower assembly as per the requirement.

Open High Limit Switch Furnace indicates the heating system turns off the fuel supply to prevent the overheating which may damage the furnace as well as create a dangerous situation inside the residence.

High Limit Switch Location

High Limit Switch Furnace is a small but very essential device used in air furnaces powered by natural gas, LP or heating oil.  

To detect the furnace Fan Limit Switch, cabinet cover should be removed. Generally it is attached to the plenum of the furnace above the combustion chamber or heat exchanger. Location of the Switch may vary as per the make and model of the Furnace.

How Does A Furnace High Limit Switch Work?

Furnace High Limit Switch protects the furnace as well as the home or business area by automatically bringing the temperature of the furnace down when it goes too high.

Acting as the key component of the furnace safety system, the two main functions of the High Limit Switch are:

• Regulation of Fan Motor: It gives the blower fan an indication when to turn on and off. When the air is heated enough, it senses the supply air temperature and tells the fan to turn on in order to circulate hot air into the home. It allows the blower to keep on running until all heated air is distributed inside the residence completely.
• Prevents from Overheating: It also identifies the supply air temperature, when the supply air temperature is too high, the components inside the furnace may get damaged. At this moment, the Limit Switch trips to shut down the system and stops furnace functions to control the temperature. In most extreme cases overheating may lead to fire hazards.

Bypass High Limit Switch Furnace

It is advice able that Fan Limit Switch or Limit Switch should be bypassed only for a temporary basis.

Limit Switch should be bypassed only for an essential reason like troubleshooting or testing purpose. A Furnace High Limit Switch acts as an essential part during the operation of a furnace by regulating the temperature, thereby it prevents the damages that may occur to the internal components of the furnace as well as maintain safety of the human being.

If we run a residential gas furnace without the Limit Switch for a long time, heat exchanger may damage and toxic gases may enter the living area of the residence. 

High Limit Switch Furnace reset

After detecting the problem associated with High Limit Switch and resolving it, the Limit Switch has to be reset for normal functioning of the furnace.

The steps to be followed for resetting the High Limit Switch Furnace are :

• At the beginning we have to close the gas valve and cut off the power supply to deactivate the system. This step is done completely for safety purpose.
• After that panel should be opened with the help of a screw driver to find the furnace’s heating duct.
• Identify the white or silver Limit Switch, remove the cover to see the body of the switch with two metal arms.
• These two arms are responsible for the high and low temperature range of the furnace.We have to identify the component in between these two arms which control the fan.
• Fix the temperature of the central component at approximately 105-115 degrees Fahrenheit. Try to ensure the fan switches off and on at accurate time.
• Now set the temperature on the left component at around 90 degree Fahrenheit, which will give indication to the left arm to stop blowing cold air when it reaches 90 degrees ,similarly set right arm at 200 degree Fahrenheit, which indicates the furnace to shut off when the burner reaches this temperature.

How to Replace?

The Furnace High Limit Switch helps to ensure your safety and the comfort of your home.

The steps to be followed to replace a defective High Limit Switch Furnace are:

1. At first we have to deactivate the furnace using service switch or circuit breaker to avoid any kind of accident.
2. After that replace the old one and fix the new Limit Switch by wiring it exactly the old Switch. It is quite simple since it has only two wires coming off and two screws are there to hold it in place. For further issues the instruction manual provided along with the Limit Switch can be followed.
3. After setting up the new Switch, furnace can be activated and regulate the thermostat to get accurate signs of the heating process of the furnace. Sufficient amount of hot air through the vent will justify smooth replacement of the Limit Switch.

How to Test High Limit Switch Furnace?

After checking all the possible reason of tripping up of the High Limit Switch Furnace and it is noticed that blower motor is working, filter is clean enough then the Limit Switch is need to be tested.

Testing of High Limit Switch Furnace is a DIY task which can be easily done with the help of a screwdriver and a multi-meter. Steps Followed to test High Limit Switch Furnace are:

• First of all deactivate the system either by turning off the serviceman switch or shutting the power off at the breaker panel.
• Opening the panel and identify the white or silver High Limit Switch.
• Disconnect the wires attached to the switch, try to remember the connection to reconnect them.
• Now with the help of a multi-meter, test if there is continuity between the two arms.

If the High Limit Switch Furnace is faulty, replace it with a new one.

In continuity test of a High Limit Switch Furnace, a multi-meter set is used to measure resistance in ohms, small electric current is sent between the switch terminals and measures the resistance between them.

Generally two possible rest results are: Zero (or near to zero),indicating switch is closed and current is flowing. Another possibility is Very High or Infinite, indicating the switch is open.

In this article we will discuss about the relationship between Boiling Point and Vapor Pressure.

Boiling point of a substance depends upon the pressure of the system and vapor pressure of a substance depends upon the temperature of the system.

In our primary school days our science textbook taught us that water boils at 100 degree Celsius. As we got to higher classes we learnt that water boils at 100 degree Celsius at atmospheric pressure at sea level and the boiling point decreases as we go higher in altitude.

This primarily explains the phenomenon of dependence of boiling point with pressure.

So, what is boiling? Physically it is the phenomenon of transformation of liquid into vapor. In order to understand boiling in a more geeky way, we must understand the other term that is vapor pressure. Vapor pressure is the pressure exerted by any liquid over its surface at a particular temperature.

This vapor pressure increases as the temperature of the liquid increases. The temperature at which vapor pressure and total pressure of the system are same is known as Boiling Point of a substance.

Is Vapor Pressure The Same as Boiling Point?

No, vapor pressure and boiling point are not same but vapor pressure is specific to a liquid and the same varies with temperature. Because of the same boiling point is also specific to a liquid.

Different liquids exert different vapor pressures at a particular temperature. The vapor pressure exerted by a liquid depends upon the intermolecular forces present between constituent molecules of the liquid.

At a certain temperature, for lower intermolecular forces in between the molecules of a liquid results higher vapor pressure exerted by the liquid. IF vapor pressure at a particular temperature is more, the boiling point of the liquid will be less. Hence, it can be concluded that although vapor pressure and boiling point are not same they are interlinked and are specific to a liquid.

What is Boiling Point and Vapor Pressure?

Boiling is characterized by vigorous evaporation of liquid to vapor, when the vapor pressure of the liquid reaches the pressure of the liquid above it, which is also called system pressure.

Under atmospheric conditions, the boiling point is also called normal boiling point.Once boiling starts, the temperature remains constant if the pressure above the liquid surface is kept constant until all the liquid is boiled off.

As shown in the picture below, the molecules in a liquid contained in a vessel are in constant motion. Some of the molecules escape the liquid surface to the atmosphere and some strike back from atmosphere to the liquid.

At a particular temperature, equilibrium is formed between the molecules escaping from the bulk liquid and those striking back to the bulk liquid.

The amount of molecules that remain in vapor space at a particular temperature depends upon the intermolecular forces of the liquid. These molecules that remain in vapor space over the liquid create the vapor pressure of the liquid.

Effect of Vapor Pressure on Boiling Point

Vapor pressure is inversely proportional to the boiling point of a liquid.

As the vapor pressure is lowered, the boiling point increases as more energy is required to vaporize the required amount of solvent to reach the system pressure. For a particular liquid, the vapor pressure is dependent on space available for solvent molecules to escape the bulk liquid at the liquid- vapor interface.

If more solid is dissolved in the liquid like in a sugar solution, less space would be available at the vapor-liquid interface for escape of solvent molecules to vapor space and hence lower vapor pressure is exerted.

This leads to requirement of higher energy to achieve the same vapor pressure as compared to pure solvent leading to higher normal boiling point.

Relation between Boiling Point and Pressure

Higher system pressure results higher boiling point and lower system pressure result lower boiling point i.e. system pressure is directly proportional to boiling point.

If the system pressure is higher, more energy would be required to create vapor pressure equivalent to the system pressure. Similarly, if System pressure is lower, boiling point is achieved at lower temperature as vapor pressure requirement is lower.

This can also be explained by change in boiling point of water with elevation difference. As shown below, water boils at 100°C at sea level at 1 atmosphere pressure.

But as we go up to a hill top, the atmospheric pressure decreases and water boils at a lower temperature. Because of the same a person cooking rice in a open vessel would need more time to cook as the cooking is taking place at lower temperatures.

On the other hand, if the cooking is carried out in a pressured system like that in a pressure cooker, the cooking is much faster as boiling takes place at higher temperature.

Why are Boiling Point and Vapor Pressure Inversely Related?

Boiling point and vapor pressure are inversely related because higher energy will be required to vaporize enough liquid into gas phase and produce a vapor pressure equivalent to system pressure (atmospheric pressure if vessel is open to atmosphere) thus reaching the boiling point.

Vapor pressure will be lower for liquids which have higher intermolecular forces and vice versa. So liquid with lower vapor pressure at a particular temperature would require higher energy requirement to overcome the intermolecular forces in liquid form and escape to vapor compared to liquids with higher vapor pressures.

Similarly, if the vapor pressure of a solvent is lowered by adding solutes into it thus reducing the exposed surface area in the vapor- liquid interface the required energy to vaporize increases. This leads to elevation of boiling point of the solution thus formed.

What Affects Vapor Pressure?

Vapor pressure for a particular liquid is dependent upon its temperature

Vapor pressure of different liquids is different for a particular temperature. Vapor pressure of few liquids is shown below at 25°C.

The vapor pressure is different for different substances because these liquids have different intermolecular forces. In general, liquids of lower densities, which will have lower molecular size and hence lower intermolecular forces have higher vapor pressure at a particular temperature.

If temperature is increased in a system, the kinetic energy of the molecules increases, as a result the molecules move rapidly and more number of molecules escape to vapor form. In this way vapor pressure increases with increasing temperature.

Vapor pressure however is not impacted by shape or size of the vessel where the liquid is kept. Foe example, a liquid in a vertical vessel or a horizontal vessel shall have same vapor pressure.

What Causes Vapor Pressure to Increase?

Vapor pressure increases with increase in temperature.

Vapor is always in equilibrium with the liquid surface below. The number of molecules in vapor form depends upon the kinetic energy of the individual molecules, which decides their probability of existing in vapor or liquid form.

For a particular liquid, if the temperature is increased the kinetic energy of the molecules in the liquid increases, making more of them eligible to overcome the intermolecular forces and exist in vapor form.

Higher number of molecules in vapor form increases the vapor pressure. A typical change of vapor pressure of water with temperature is shown in the image below.

Factors Affecting Boiling Point

The factors that affect boiling point are pressure, impurities in liquid and liquid intermolecular forces.

If the system pressure is higher, more heat would be required to increase the vapor pressure of the liquid to achieve the system pressure. Boiling point impact on external pressure for water is shown by the curve below.

If we consider, a pure solvent and same solute with impurities, the boiling point of the pure solvent is always less. It is because more surface area available for a pure solvent for vapor to escape the liquid state compared to solute with impurities, where some of the sites in vapor liquid interface are occupied.

A liquid having larger molecules with higher intermolecular forces will have higher boiling point. This is because less vapor can break free above the liquid surface by overcoming the intermolecular forces at a particular temperature compared to liquid with smaller constituent molecules having lower intermolecular forces.

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In a refrigeration system, normal discharge pressure is defined as the pressure at which condensation takes place as per the design

At the normal discharge pressure, it is assumed that the refrigeration would be most energy efficient and there would be no fouling in the condensing circuit. Operating a compressor at significantly away from the normal discharge pressure values might be detrimental to compressor’s health.

For a compressor to operate at normal discharge pressure, following must be fulfilled:

• Right amount of refrigerant: The quantity of the refrigerant loaded must be correct. Too high a refrigerant load increases the discharge pressure and too low a refrigerant load decreases the discharge pressure.
• Both suction and discharge valves of compressor must be leak proof: If the discharge valve is passing a part of refrigerant would sneak back into the cylinder and keep recirculating inside the compressor increasing the discharge temperature and reducing the discharge pressure.Similarly, if the suction valve is passing there will be malfunction in the compressor upstroke.
• The compressor piston rings should not leak: IF the discharge gases leaks through the piston rings it leads to lower discharge pressure.
• Condenser should not be in fouled condition: A fouled condenser leads to higher discharge pressure because of inefficient cooling
• Sufficient cooling utility: Even if the condenser is fine, insufficient cooling water flow and temperature for a water cooled system and high ambient temperature for air cooled system may lead to higher than normal discharge temperatures.

What is Normal Discharge Pressure?

Normal discharge pressure is defined as the pressure at the discharge of refrigeration compressor, for which the refrigeration system is designed.

Since at the discharge of the refrigeration compressor the condenser is located, normal discharge pressure can also be defined as the pressure at which the refrigerant condenses with specified amount of sub-cooling at the available cooling utility.

Thus, the normal discharge pressure depends upon the refrigeration system, which includes the refrigerant in use and temperature of cooling utility.

 If cooling utility is air, the discharge pressure would depend on specified ambient air temperature and it cooling utility is water, then it shall depend upon the available cooling water temperature.

 The discharge pressure would also depend upon the type of refrigerant use.

The efficiency of refrigeration system in terms of power consumption are highest when operating at normal discharge pressure providing optimum cooling capacity for which it is designed.

 However, for example, normally the Ammonia based refrigeration systems are designed for normal discharge pressures of 95-100 Psig.

Normal Discharge Pressure Cause

Normal discharge pressure is the default pressure of a refrigeration system and it is more important to ponder what causes the discharge pressure to increase.

Speaking of normal discharge pressure, from energy conservation point of view it is however always preferred to have a discharge pressure lower than the normal. Lowering discharge pressure requires higher cooling duty to condense the refrigerant.

As a thumb rule for each °F decrease in condensing temperature, compressor power consumption decreases by 1%.

There are several causes that can lead to higher than normal discharge pressure. The primary and most common among them is the fouling of the condenser coils. Fouled condenser coils leads to lower cooling of refrigerant cause higher back pressure to the compressor.

The second common cause of higher discharge pressure, is topping up of higher than required refrigerant into the system. Higher refrigerant load makes a part of condenser ineffective by reducing the condensing area.

This leads to higher sub-cooling of refrigerant but higher back-pressure to compressor due to lower effective condensing surface area.

The third but less common condesnder malfunction leading to higher back-pressure to the compressor , is build-up of non-condensable in the refrigeration system.

Low suction pressure and Normal Discharge Pressure

The easiest way to detect low suction pressure in a refrigeration compressor is to look for frosting in the suction line.

The frosting in the suction line happens due to excessive cooling as a result of lower refrigerant flow. Lower refrigerant flow can also happen due to minor leaks in the system taking place over a long period of time.

There are other reasons too which may lead to lower suction pressure. If the suction line or liquid line is made too long or installation of these lines are such that it leads to a pressure drop large enough to cause the liquid flash upstream of the expansion valve.

The expansion valve is normally designed to allow liquid flow and if vapor is encountered instead, the amount of refrigerant would be lower than design thus reducing the suction pressure.

 Similarly, an inadequately sized suction line can lead to lower suction pressure due to higher pressure drop.

Low suction pressure is also encountered because of low evaporator load. This may be because of fouling in air distribution system or circulating air being too cold.

How to calculate Discharge Pressure?

Discharge pressure or head pressure is the pressure generated on the output side of a gas compressor in a refrigeration or air conditioning system.

The discharge pressure of a refrigeration compressor can be calculated based on Cooling media availability and desired temperature drop of system being cooled.

In the above statement, if the cooling media is ambient air, the ambient air temperature is required and if cooling media is water, the cooling water temperature is required.

For water cooled systems, the discharge pressure requirements are generally lower than air cooled systems for same indoor temperature.

Consider the case of a R-22 refrigerant system, where the ambient temperature is 95°F and indoor temperature to be maintained is 85°C. As a thumb rule, the condensing temperature can be considered to be 30° F + Amb = 125°F. The corresponding saturation pressure for R-22 refrigerant is 279 psi from the R-22  Pressure temperature chart.

Rack and pinion is a mechanical system that is widely used in various applications, ranging from steering systems in automobiles to industrial machinery. It is a simple yet effective mechanism that converts rotational motion into linear motion. In this section, we will explore the definition and function of rack and pinion, as well as its working principle.

Definition and function of Rack and Pinion

A rack and pinion is a type of gear mechanism that consists of a toothed bar, known as the rack, and a gear, known as the pinion. The rack has straight teeth that mesh with the teeth of the pinion, allowing for smooth and precise motion transfer.

The primary function of a rack and pinion system is to convert rotational motion into linear motion. When the pinion gear rotates, it engages with the teeth of the rack, causing the rack to move in a linear direction. This linear motion can be used to perform various tasks, such as steering a vehicle or moving a load in an industrial setting.

One of the most common applications of rack and pinion is in the steering systems of automobiles. In a rack and pinion steering system, the rotational motion of the steering wheel is transferred to the pinion gear, which then moves the rack back and forth. This motion is transmitted to the wheels, allowing the driver to control the direction of the vehicle.

Rack and pinion systems are also used in other applications, such as robotics, CNC machines, and conveyor systems. In these cases, the linear motion provided by the rack and pinion mechanism is utilized to move objects or perform specific tasks with precision and accuracy.

Working principle of Rack and Pinion

The working principle of a rack and pinion system is relatively straightforward. When the pinion gear rotates, its teeth engage with the teeth of the rack, causing the rack to move in a linear direction.

To understand this principle better, imagine a scenario where you have a rack and pinion mechanism with a stationary rack and a rotating pinion. As the pinion gear rotates, its teeth push against the teeth of the rack, causing the rack to move in the direction determined by the rotation of the pinion.

The direction of the linear motion depends on the orientation of the teeth on the rack and pinion. If the teeth are angled in a way that the pinion rotates clockwise, the rack will move in one direction. Conversely, if the teeth are angled in a way that the pinion rotates counterclockwise, the rack will move in the opposite direction.

The precision and smoothness of the motion in a rack and pinion system are determined by the quality of the gear teeth and the lubrication used. Proper maintenance and regular inspection of the rack and pinion mechanism are essential to ensure optimal performance and longevity.

Applications of Rack and Pinion

Rack and pinion systems are widely used in various applications due to their simplicity, efficiency, and reliability. Let’s explore some of the common areas where rack and pinion mechanisms find their application.

Steering Mechanism

One of the most well-known applications of rack and pinion is in the steering systems of vehicles. In this mechanism, the rack is a linear gear that meshes with a pinion gear attached to the steering column. As the driver turns the steering wheel, the pinion gear rotates, causing the rack to move linearly. This linear motion is then translated into the rotational motion of the vehicle’s wheels, allowing for precise control and maneuverability.

Rack and pinion steering systems offer several advantages over other steering mechanisms. They provide a direct and responsive steering feel, making it easier for drivers to navigate tight turns and parking spaces. Additionally, rack and pinion systems are compact, lightweight, and require minimal maintenance, making them ideal for a wide range of vehicles, from small cars to heavy-duty trucks.

Industrial Machinery

Rack and pinion mechanisms are extensively used in various industrial machinery applications. These systems are commonly employed in machine tools, such as milling machines, lathes, and CNC routers, to convert rotary motion into linear motion. By coupling a pinion gear to a rack, these machines can accurately position and move their cutting tools or workpieces along a linear axis.

The precise and repeatable motion provided by rack and pinion systems makes them suitable for applications that require high accuracy and tight tolerances. Industries such as manufacturing, woodworking, metalworking, and automation heavily rely on rack and pinion mechanisms to achieve efficient and precise operations.

Transportation Systems

Rack and pinion systems also play a crucial role in various transportation systems, particularly in funicular railways and cable cars. In these systems, a rack railway is used to provide traction and control the movement of the vehicles. The pinion gear, driven by an electric motor or hydraulic system, engages with the rack, allowing the vehicles to ascend or descend steep slopes safely.

The use of rack and pinion in transportation systems ensures reliable and secure operation, even in challenging terrains. These mechanisms offer excellent traction, preventing slippage and ensuring the safety of passengers and cargo. Additionally, rack and pinion systems enable precise speed control and smooth acceleration and deceleration, enhancing the overall comfort and efficiency of the transportation system.

Other Applications

Apart from the aforementioned examples, rack and pinion mechanisms find applications in various other fields. Some notable examples include:

• Robotics: Rack and pinion systems are often utilized in robotic arms and manipulators to achieve precise and controlled movements.

• Elevators: Rack and pinion systems are employed in elevator mechanisms to facilitate vertical transportation in buildings and other structures.

• Material Handling: Rack and pinion systems are utilized in conveyor systems, cranes, and hoists to move heavy loads efficiently and safely.

• Stage and Theater Equipment: Rack and pinion mechanisms are commonly used in stage curtains, scenery movement, and other theatrical applications.

Advantages and Disadvantages of Rack and Pinion

Rack and pinion is a popular mechanism used in various applications, ranging from steering systems in automobiles to industrial machinery. This mechanism offers several advantages and disadvantages, which we will explore in this section.

Advantages

Rack and pinion systems provide numerous benefits that make them a preferred choice in many applications. Let’s take a closer look at some of these advantages:

1. Simplicity and Efficiency: One of the key advantages of rack and pinion is its simple design. The mechanism consists of a rack (a linear gear) and a pinion (a circular gear). This simplicity allows for easy installation and maintenance. Moreover, the direct transfer of motion from the pinion to the rack ensures high efficiency, minimizing energy loss.

2. Precise and Responsive: Rack and pinion systems offer excellent precision and responsiveness. The direct contact between the rack and pinion results in immediate and accurate motion transfer. This makes rack and pinion ideal for applications that require precise control, such as steering systems in vehicles.

3. Compact Size: Rack and pinion mechanisms are compact, making them suitable for applications with limited space. The linear motion of the rack allows for a more compact design compared to other types of gear systems. This advantage is particularly valuable in industries where space optimization is crucial.

4. Smooth Operation: Rack and pinion systems provide smooth and uniform motion. The teeth of the pinion engage with the rack, ensuring a consistent transfer of force. This smooth operation reduces noise and vibration, enhancing the overall user experience.

5. Versatility: Rack and pinion mechanisms find applications in a wide range of industries. From steering systems in automobiles to robotics, CNC machines, and even elevators, the versatility of rack and pinion makes it a popular choice across different sectors.

Disadvantages

While rack and pinion systems offer numerous advantages, they also have a few limitations. Let’s explore some of the disadvantages associated with this mechanism:

1. Limited Load Capacity: Rack and pinion systems may have limitations when it comes to handling heavy loads. The teeth of the pinion and rack can experience excessive wear and tear under high loads, leading to reduced lifespan and potential failure. In such cases, alternative mechanisms, such as ball screws or hydraulic systems, may be more suitable.

2. Backlash: Backlash refers to the slight play or clearance between the teeth of the rack and pinion. This can result in a small amount of lost motion or imprecision. While modern rack and pinion systems have minimized backlash, it can still be a concern in applications that require extremely precise positioning.

3. Maintenance: Although rack and pinion systems are relatively easy to install and maintain, they do require periodic lubrication to ensure smooth operation and prevent premature wear. Failure to perform regular maintenance can lead to increased friction, noise, and reduced lifespan of the mechanism.

4. Cost: Depending on the specific application and requirements, rack and pinion systems can be more expensive compared to other alternatives. Factors such as material quality, precision, and load capacity can influence the overall cost. It is important to carefully consider the cost-benefit ratio when choosing rack and pinion for a particular application.

Types of Rack and Pinion

Rack and pinion systems are widely used in various applications due to their simplicity and effectiveness. There are different types of rack and pinion mechanisms, each with its own unique characteristics and advantages. Let’s explore some of the most common examples:

Straight Teeth

One of the simplest and most commonly used types of rack and pinion is the straight teeth design. In this configuration, the pinion gear has straight teeth that mesh with a straight rack. This type of rack and pinion mechanism provides a smooth and efficient transfer of motion.

The straight teeth design is often used in applications where precision and accuracy are crucial, such as in CNC machines, robotics, and industrial automation. It offers excellent positioning capabilities and can handle heavy loads with ease. Additionally, the straight teeth design is relatively easy to manufacture and maintain.

Helical Teeth

Another popular variation of the rack and pinion mechanism is the helical teeth design. In this configuration, both the pinion gear and the rack have helical teeth that mesh together. The helical teeth are cut at an angle, allowing for a smoother and quieter operation compared to straight teeth.

The helical teeth design offers improved load-carrying capacity and higher efficiency due to the increased contact area between the gear and the rack. This makes it suitable for applications that require high-speed and high-torque operations, such as automotive steering systems and machine tools.

Roller Pinion

The roller pinion system is a unique variation of the rack and pinion mechanism that utilizes rollers instead of teeth. The rack consists of a series of rollers that engage with the pinion gear, which has matching grooves. This design provides a smooth and precise motion transfer with minimal backlash.

The roller pinion mechanism offers several advantages over traditional rack and pinion systems. It has a higher positional accuracy, lower friction, and longer lifespan due to reduced wear. This makes it ideal for applications that demand high precision and durability, such as in semiconductor manufacturing and medical equipment.

Design Considerations for Rack and Pinion

When it comes to designing a rack and pinion system, there are several important considerations to keep in mind. These considerations will help ensure that the system functions properly and efficiently. In this section, we will discuss two key design considerations: module and pitch, and pinion size and material.

Module and Pitch

The module and pitch of a rack and pinion system are crucial factors that determine the system’s performance and compatibility. The module refers to the size of the teeth on the gear, while the pitch is the distance between corresponding points on adjacent teeth. Let’s take a closer look at each of these considerations:

• Module: The module of a rack and pinion system is determined by the size and strength requirements of the application. It is important to choose a module that can handle the load and torque requirements of the system. A larger module will generally result in a stronger and more durable system, but it may also increase the size and weight of the components. On the other hand, a smaller module can provide a more compact and lightweight system, but it may not be as robust. Therefore, it is crucial to strike a balance between strength and size when selecting the module for your rack and pinion system.

• Pitch: The pitch of a rack and pinion system determines the smoothness of its operation. A smaller pitch will result in a finer resolution and smoother motion, but it may also reduce the system’s load-carrying capacity. Conversely, a larger pitch will provide a higher load-carrying capacity but may result in a less smooth motion. The pitch should be chosen based on the specific requirements of the application. For example, applications that require precise positioning, such as CNC machines, may benefit from a smaller pitch, while applications that require high load-carrying capacity, such as heavy machinery, may require a larger pitch.

Pinion Size and Material

The size and material of the pinion are also important considerations in rack and pinion system design. Let’s explore these factors in more detail:

• Size: The size of the pinion is determined by the torque and load requirements of the system. A larger pinion can handle higher loads and torques, but it may also increase the size and weight of the system. On the other hand, a smaller pinion can provide a more compact and lightweight system, but it may have limitations in terms of load-carrying capacity. It is essential to select a pinion size that strikes a balance between the system’s requirements and the desired size and weight.

• Material: The material of the pinion plays a crucial role in its durability and performance. Common materials used for pinions include steel, brass, and plastic. Steel pinions are known for their strength and durability, making them suitable for heavy-duty applications. Brass pinions offer good wear resistance and are often used in applications that require smooth and quiet operation. Plastic pinions, on the other hand, are lightweight and cost-effective, making them suitable for applications where weight and cost are important factors. The choice of pinion material should be based on the specific requirements of the application, considering factors such as load, speed, and environmental conditions.

Common Steering Rack Problems

The steering rack is a crucial component of a vehicle‘s steering system, responsible for converting the rotational motion of the steering wheel into the linear motion needed to turn the wheels. While rack and pinion steering systems are generally reliable, they can experience certain problems over time. In this section, we will explore some of the common steering rack problems that car owners may encounter.

1. Leaking Power Steering Fluid

One of the most common issues with a steering rack is a leak in the power steering system. Power steering fluid is essential for smooth and effortless steering, as it helps to reduce friction and provide hydraulic assistance. However, over time, the seals in the steering rack can wear out or become damaged, leading to fluid leakage.

When power steering fluid leaks from the rack, you may notice a puddle of fluid underneath your vehicle or a drop in the power steering fluid level. In addition, you may experience difficulty in steering, a whining noise when turning the wheel, or a jerky steering response. It is important to address a power steering fluid leak promptly, as low fluid levels can cause further damage to the steering system.

2. Excessive Play or Loose Steering

Another common problem with steering racks is excessive play or loose steering. This can occur due to wear and tear on the rack and pinion mechanism, which can lead to a gap between the teeth of the rack and the pinion gear. As a result, you may notice that the steering wheel feels loose or has a significant amount of play before the wheels respond to your input.

Excessive play in the steering can make the vehicle feel unstable and can affect your ability to control the direction of the vehicle. It is important to have this issue addressed by a qualified mechanic, as it may require replacing worn-out components or adjusting the steering system.

3. Uneven Tire Wear

A faulty steering rack can also cause uneven tire wear. When the steering rack is not functioning properly, it can result in the wheels being misaligned or not turning at the same rate. This can lead to uneven tire wear, with some tires wearing out faster than others.

Uneven tire wear not only affects the performance and handling of the vehicle but also reduces the lifespan of the tires. Regularly inspecting your tires for signs of uneven wear, such as excessive wear on the inner or outer edges, can help identify potential steering rack issues early on.

4. Steering Wheel Vibration

If you notice a vibration in the steering wheel while driving, it could be a sign of a problem with the steering rack. Steering wheel vibration can occur due to various reasons, including worn-out tie rod ends, misalignment, or a damaged steering rack.

A worn-out or damaged steering rack can cause the wheels to vibrate, especially at higher speeds. This vibration can be felt through the steering wheel, making the driving experience uncomfortable and potentially unsafe. It is important to have the steering system inspected and repaired if you experience steering wheel vibration.

5. Difficulty Turning or Stiff Steering

Difficulty turning the steering wheel or stiff steering is another common steering rack problem. This can be caused by various factors, such as a lack of power steering fluid, a malfunctioning power steering pump, or a worn-out steering rack.

If you find it challenging to turn the steering wheel, especially at low speeds or when parking, it is essential to have the steering system checked. Ignoring this issue can lead to further damage to the steering components and potentially compromise your safety on the road.

Examples of Rack and Pinion Gears in Everyday Life

Rack and pinion gears are widely used in various applications, ranging from car steering systems to industrial machinery. Let’s explore some common examples of how these gears are utilized in our everyday lives.

Car Steering Systems

One of the most well-known applications of rack and pinion gears is in car steering systems. In this setup, the steering wheel is connected to a pinion gear, which engages with a rack gear. As the driver turns the steering wheel, the pinion gear rotates, causing the rack gear to move either left or right. This motion is then transmitted to the car‘s wheels, allowing for precise control and maneuverability.

Elevators

Another example of rack and pinion gears in action can be found in elevators. Rack and pinion systems are often used to control the vertical movement of elevators. The pinion gear is connected to the elevator car, while the rack gear is fixed along the elevator shaft. When the pinion gear rotates, it moves the elevator car up or down along the rack gear, providing a smooth and reliable means of transportation between floors.

Measuring Instruments

Rack and pinion gears are also utilized in various measuring instruments, such as calipers and micrometers. These gears enable precise and accurate measurements by converting rotational motion into linear motion. By turning the pinion gear, the rack gear moves, allowing for precise adjustments and measurements to be made.

Industrial Machinery

In the realm of industrial machinery, rack and pinion gears play a crucial role in many applications. For example, they are commonly used in CNC machines, where they help control the movement of the cutting tool. By converting rotational motion into linear motion, rack and pinion gears enable precise and controlled movements, resulting in accurate machining operations.

Transportation Systems

Rack and pinion gears are also found in various transportation systems, such as funicular railways and tramways. These gears are used to control the movement of the vehicles along the tracks. The pinion gear engages with the rack gear, allowing for smooth and efficient transportation of passengers or goods.

Gates and Silos

Rack and pinion gears are often employed in gates and silos to control their opening and closing mechanisms. By rotating the pinion gear, the rack gear moves, enabling the precise positioning of gates or the controlled release of materials from silos. This ensures efficient operation and prevents any potential accidents or spillages.

Stair Lifts

Stair lifts, which are commonly used to assist individuals with mobility challenges, also rely on rack and pinion gears. These gears enable the smooth and controlled movement of the stair lift along the staircase. By turning the pinion gear, the rack gear moves, allowing for a safe and comfortable ascent or descent of the stairs.

Actuators

Rack and pinion gears are frequently used in actuators, which are devices that convert electrical or hydraulic power into mechanical motion. These gears play a crucial role in translating the rotational motion of the actuator into linear motion, enabling precise control and movement in various applications, such as robotics and automation systems.

Woodworking and Metal Cutting Machines

In woodworking and metal cutting machines, rack and pinion gears are often employed to control the movement of the cutting tool or workpiece. By converting rotational motion into linear motion, these gears enable precise and controlled movements, resulting in accurate and efficient cutting operations.

How to Center a Rack and Pinion

If you’ve noticed that your vehicle’s steering feels off-center or imbalanced, it may be time to center your rack and pinion system. Centering the rack and pinion ensures that the steering wheel is aligned with the wheels, providing a smooth and controlled driving experience. Here are the steps to center the steering rack and pinion:

1. Locate the Adjustment Nut: Start by finding the adjustment nut on the rack and pinion assembly. This nut is typically located on the driver’s side of the vehicle, near the firewall. It may be covered by a rubber boot for protection.

2. Raise the Front Wheels: Use a jack to lift the front of the vehicle off the ground. Ensure that the vehicle is securely supported on jack stands before proceeding. This step is crucial to allow the wheels to move freely during the centering process.

3. Access the Adjustment Nut: Depending on the vehicle, you may need to remove any covers or panels to access the adjustment nut. Refer to the vehicle’s manual for specific instructions on how to access the nut.

4. Turn the Adjustment Nut: With the wheels off the ground and the adjustment nut accessible, use a wrench or socket to turn the nut. The direction in which you turn the nut will depend on the type of rack and pinion system in your vehicle. Consult the vehicle’s manual or a trusted mechanic for guidance.

5. Check the Steering Wheel Alignment: After making adjustments to the adjustment nut, lower the vehicle back to the ground. Sit in the driver’s seat and check the alignment of the steering wheel. It should now be centered and aligned with the wheels. If it is still off-center, repeat the adjustment process until the steering wheel is properly centered.

6. Test Drive: Take your vehicle for a test drive to ensure that the steering feels balanced and responsive. Pay attention to any unusual vibrations or noises, as these may indicate further issues with the rack and pinion system.

It’s important to note that centering a rack and pinion system requires precision and accuracy. If you’re unsure about performing this task yourself, it’s recommended to seek the assistance of a qualified mechanic. They have the expertise and specialized tools to ensure the rack and pinion is centered correctly.

By following these steps, you can effectively center your rack and pinion system, improving the overall steering performance of your vehicle. Remember to always prioritize safety and consult the vehicle’s manual for any specific instructions or precautions.

Rack and Pinion Calculation Example

In order to understand how rack and pinion systems work, it’s important to have a grasp of the calculations involved in determining gear ratio and force transmission. Let’s take a look at an example calculation to illustrate these concepts.

Let’s say we have a rack and pinion mechanism that is being used in a steering system. The rack has 20 teeth, while the pinion has 4 teeth. We want to determine the gear ratio and the force transmitted when a force of 100 Newtons is applied to the pinion.

To calculate the gear ratio, we can use the formula:

Gear Ratio = Number of Teeth on Rack / Number of Teeth on Pinion

Plugging in the values from our example, the gear ratio would be:

Gear Ratio = 20 / 4 = 5

This means that for every revolution of the pinion, the rack will move 5 times.

Now let’s move on to calculating the force transmitted. The force transmitted can be determined using the formula:

Force Transmitted = Applied Force * Gear Ratio

Substituting the values from our example, we get:

Force Transmitted = 100 N * 5 = 500 N

Therefore, when a force of 100 Newtons is applied to the pinion, the rack will experience a force of 500 Newtons.

It’s important to note that these calculations are simplified examples and do not take into account factors such as friction and efficiency. In real-world applications, these factors need to be considered for accurate calculations.

By understanding these calculations, engineers and designers can determine the appropriate gear ratio and estimate the force that will be transmitted in a rack and pinion system. This knowledge is crucial in ensuring the system functions optimally and meets the desired requirements.

In the next section, we will explore some practical examples of rack and pinion applications in various industries.

Frequently Asked Questions

Q: Where can a rack and pinion be used?

A: A rack and pinion system can be used in various applications such as steering systems in automobiles, CNC machines, robotics, and industrial machinery.

Q: How does a rack and pinion system work?

A: In a rack and pinion system, a gear called a pinion meshes with a linear toothed component called a rack. When the pinion rotates, it translates the rotational motion into linear motion along the rack.

Q: How to center a steering rack and pinion?

A: To center a steering rack and pinion, you need to turn the steering wheel to its neutral position and adjust the tie rods until the wheels are straight and aligned.

Q: What is rack in rack and pinion?

A: In a rack and pinion system, the rack refers to the linear toothed component that meshes with the pinion gear. It converts rotational motion into linear motion.

Q: How to design a rack and pinion?

A: Designing a rack and pinion involves determining the required gear ratio, tooth profile, module, and pitch diameter based on the application requirements. It also involves considering factors such as load, speed, and backlash.

Q: What are the applications of rack and pinion?

A: Rack and pinion systems find applications in various fields, including automotive steering, industrial machinery, robotics, CNC machines, and even some household appliances.

Q: What are some common steering rack problems?

A: Common steering rack problems include leaks in the hydraulic system, worn-out or damaged rack bushings, loose or damaged tie rods, and excessive play in the steering wheel.

Q: Can you provide examples of rack and pinion gears in everyday life?

A: Sure! Some examples of rack and pinion gears in everyday life include power steering systems in cars, sliding gates, elevators, and even some exercise equipment like rowing machines.

Q: Can you list an example where the rack and pinion mechanism might be used?

A: One example where the rack and pinion mechanism might be used is in the steering system of a go-kart. The rack and pinion system provides precise and responsive steering control.

Q: What are the different types of rack and pinion?

A: The different types of rack and pinion include straight (spur) rack and pinion, helical rack and pinion, circular rack and pinion, and rack and pinion with a non-circular gear profile. Each type has its own advantages and applications.

Q: Can you provide an example sentence using “rack and pinion”?

A: “The rack and pinion steering system in the car ensured smooth and precise control while navigating tight corners.”

In this article we will discuss about the relationship of Mass Flow Rate to Velocity.

The concept of flow rate(Mass Flow rate and Volume Flow Rate) measurement in a industry is very much essential for accurate and cost effective running of a process. Velocity indicates how fast a fluid is moving a distance per unit time.

Whenever we calculate flow rate of a fluid flowing through a pipe line certain terms like mass flow rate, volumetric flow rate, Molar flow rate, velocity, density, volume ,temperature , pressure etc come into the picture.

Flow rates and all the above mentioned physical properties are inter related and we can determine one quantity from the other by using different formulas associated with them.

Velocity=Distance traveled /Time

Volume Flow Rate, Q= Area x Velocity

Mass Flow Rate, ṁ=Density x Area x Velocity

Mass Flow Rate

Mass Flow Rate is the measurement of mass of a fluid passing through a passage per unit time.

Mass Flow rate can be expressed as,

ṁ=mass/time=m/t

SI unit of mass flow rate is Kg/s and it is denoted by ṁ.

Accurate measurement of Mass flow rate is necessary in an industry to control the different operations smoothly. Efficiency of an equipment and product quality also depends on mass flow rate of a fluid.

Mass is neither created nor destroyed and Mass flow rate is not affected by temperature and pressure change during the process so in case of precision measurement mass flow measurement is always advisable.

Mass Flow Rate to Velocity relationship

Flow rate measurement of different fluids is an important aspect of pipe line industries.

Velocity is the measurement of how fast a fluid is moving per unit of time. Mass Flow Rate is associated with the amount of fluid passing through a passage per unit time.

Mass Flow Rate can be expressed as ṁ=mass/time=m/t Eq1

And Volume Flow rate can be expressed as  Q= volume/time= V/t   Eq2

                                          From Eq(1), ṁ=mass/volume . volume/time Eq3

                                            Now, mass/volume=Fluid density ρ

                                            And volume/time=Volumetric Flow Rate=Q

                                             From Eq(3) , ṁ= ρ.Q         Eq4

The above equation relates Mass Flow rate and Volumetric Flow Rate of a fluid. If we know the density of the fluid and discharge through a pipe, then we can determine the amount of fluid passing through the pipe in terms of Kg/s i.e. mass flow rate of the fluid.

  From the Continuity Equation applicable for incompressible fluid we can write,

  Here A is the cross sectional area of the passage and bar(v) is the average velocity of the fluid.

 So Eq(4) becomes, 

From the Eq(5) it is clear that mass flow rate of a liquid is directly proportional to the density of the liquid, velocity of the liquid and the cross sectional area.

How to Calculate Mass Flow Rate from Velocity?

The Flow rates, velocity, pressure, density all these terms are interrelated to each other.

If we know the velocity(v)of a flow through a pipe of cross sectional area(A), then we can calculate the volume flow rate of the fluid by using following formula,

Where Q=Volume Flow rate

A= Cross sectional area of the pipe

= Average velocity of the fluid

Now Mass Flow Rate is the density ρ multiplied by the Volume Flow Rate

ṁ=ρ. Q or,

As per the law of conservation of mass, in case of incompressible fluid passing through a channel of non uniform cross sectional area, the Mass flow rate maintains a constant value.

In the above figure we can observe a pipe with different cross sectional area A1 and A2 (where A1>A2) through which water(incompressible in nature) is flowing.

Even though the diameter of the pipe is not same, due to continuity same amount of water is passing through the point 1 and 2. The speed of the fluid is less at the wider area of the passage than the speed at the narrow region to keep the flow constant. 

At point 1 and 2,

Q_{1}=Q_{2} or,

This is the famous Continuity Equation applicable for Incompressible fluids.

Difference between Mass Flow Rate and Velocity

The difference between Mass Flow Rate and Velocity as follows:

Problems Related to Mass Flow Rate

 Problem 1: A fluid with density 650 kg/m³ is flowing through a duct of inner cross sectional area 25 cm² with a velocity of 30 m/s. Find the mass flow rate of the fluid.

Solution: Here, Density, ρ=650kg/m³

Cross sectional Area, A=25 cm²=0.25m²

Velocity, v=30m/s

The formula for calculating mass flow rate ṁ= ρVA

\dot{m}=  650× 30 × 0.25m = 8400 kg/s

The mass flow rate m  for the above-given data is 4875 kg/s

Problem 2:The mass flow rate of a fluid flowing through a circular pipe is 3600 kg/s, the velocity of the flow is 25 m/s and cross sectional area of the pipe is  10 cm². Calculate the density of the fluid inside the pipe.

Solution:

From the given data,

\dot{m}=  3600 kg/s,

Velocity,v = 25 m/s and

Area of the cross section,A = 10 cm² = 0.10m²

To determine the density of thefluid from the above-given values, we can use the formula,

Density ρ= m/vA

ρ = 3600 / ( 25 * 0.10 ) =  3600 / 2.5

ρ =  1440 kg/m³

The density of the liquid ρ of the fluid passing through the pipe is 1440kg/m³

Frequently Asked Questions(FAQs)

Q1: Write the differences between Mass Flow Rate and Volume Flow Rate.

Answer: The Differences between Mass Flow Rate and Volume Flow Rate are mentioned below:

To know more about Mass Flow Rate(Click here)