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.
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.