Hello everyone! Today’s article will discuss control valve accessories, which are important for beginners and engineers with 2-3 years of experience.
Control Valve Accessories
The list of control valve accessories
- Air filter regulator
- Handwheel
- Solenoid valve
- Proximity sensor
- Limit switch
- Positioner
- Air volume booster
- Air lock-up relay
- Quick exhaust valve
- Trip valve
- Instrument air volume tank
Let’s take a quick look at control valve accessories, which can be used with on-off valves as well.
1. Air filter regulator
An air filter regulator (AFR) is used in valve inlets to remove dirt particles and maintain air pressure for valve operation in instrument air inlet lines.
2. Handwheel
The handwheel is a commonly used component in valves. Its main function is to manually operate the valve when the valve cannot be operated using the actuator due to issues like the actuator passing a body jam or the valve getting stuck.
If there is an emergency, you can utilize the handwheel to operate the valve.
3. Solenoid valve
A solenoid valve is a small but important type of on-off valve that comes in various forms. Its primary function is to start, stop, or redirect the flow of instrument air.
The solenoid valve plays a crucial role in the ESD (Emergency Shutdown) system, receiving commands from it to take immediate emergency action when necessary.
4. Proximity sensor
The proximity sensor is a type of non-contact sensor that is used to determine the status of a valve in the field.
It is used in the digital input loop to detect whether the valve is open or closed. In most cases, two proximity sensors are used for each valve. One for open feedback and the other for closed feedback.
5. Limit switch
The limit switch determines whether a valve is open or closed. When the valve stem reaches the switch, it presses against it. Two limit switches are used for opening and closing a valve.
6. Positioner
A positioner is a device that is used to control valves. It receives signals from the control room, such as 4 mA to 20 mA or FF, and provides the appropriate instrument air to the actuator to operate the control valve.
To ensure accurate positioning of the control valve, the positioner has a feedback assembly inside it.
In the current market, smart positioners are available which include I to P, relay, and other components inside them. In the past, only pneumatic positioners were available which did not have the I to P component.
7. Air volume booster
An air volume booster is one of the very important valve accessories. In the instrument air tube of the positioner, generally ¼” tube is used.
So, the volume of the instrument air to operate a large valve will be very little and the valve will take more time to open or close.
So, an air volume booster is used to increase the volume of the air only. The pressure will remain the same.
8. Air lock-up relay
The air lock-up relay secures instrument air in case of main air failure.
If the reference air pressure drops below the set pressure, the relay blocks and locks air in the actuator.
9. Quick exhaust valve
A quick exhaust valve is a mechanism that helps in releasing air quickly from the actuator, thereby making the actuator move faster.
This valve works in two ways – it allows air to flow normally in one direction towards the actuator.
On the other hand, when the inlet instrument air from that direction is stopped, the valve opens and releases the air from the actuator in the opposite direction with a much higher flow rate towards the atmosphere.
10. Trip valve
A trip valve is used to take the valve to the desired position or fail-safe state in case of instrument air failure.
The fail-safe condition can be configured using a trip valve. The trip valve needs an instrument air volume tank that stores instrument air.
11. Instrument air volume tank
The instrument air volume tank holds instrument air which can be used in case of emergency. This instrument air is used by a trip valve to take fail action in case of loss of instrument air.
EndNote
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