What accessories are needed for control valves?

The introduction of the main accessories of the control valve:

Regulating valve positioner is the main accessory of the pneumatic actuator. It is used together with a pneumatic actuator to improve the positional accuracy of the valve, to overcome the friction of the valve stem and the influence of the unbalance force of the medium, and to ensure that the valve is correctly positioned by the signals from the regulator. 

In the following cases, the positioner should be equipped:

1. When the medium pressure is high, and the differential pressure is large;

2. When the caliber of the regulating valve is large (DN>100);

3. High or low-temperature control valves;

4. When there is a need to increase the operating speed of the regulating valve;

5. When operating an actuator with a non-standard spring using a standard signal (spring range other than 20 to 100 KPa);

6. When used for split-range control

7. When the valve is to be operated in the reverse direction (air-closed type and air-open type can be converted to each other);

8. When it is necessary to change the flow characteristics of the valve (the positioner cam can be changed);

9. When there is no spring or piston actuator, and proportional action is to be realized

10. When electrical signals are used to operate pneumatic actuators, electrical-pneumatic valve positioners must be distributed.

Solenoid valves:

When the system needs to achieve program control or two-position control, it is necessary to use solenoid valves. Selection of solenoid valves, in addition, to considering AC and DC power supply and voltage, and frequency, must pay attention to solenoid valves and regulating the role of the valve type of relationship, can be equipped with "normally open" or "normally closed."

Suppose you need to increase the capacity of the solenoid valve to shorten the action time. In that case, you can use two solenoid valves or solenoid valves as a pilot valve and large-capacity combination of pneumatic relays.

Pneumatic Relay:

A pneumatic relay is a kind of power amplifier, it can send the pneumatic signal to a distant place, eliminate the lag caused by the lengthening of the signal pipeline, mainly used between the field transmitter and the central control room of the regulating instrument, or between the regulator and the field regulating valve, and there is also a role is to amplify or reduce the signal.   

Converters:

The converter is divided into gas-electricity converter and electricity-gas converter, whose function is to realize a specific relationship between gas and electric signals to convert each other. It is mainly used to convert 0～10mA or 4～20mA electric signals or convert 0～100KPa gas signals into 0～10mA or 4～20mA electric signals when manipulating pneumatic actuators with electric signals.

Air Filtration Pressure Reducing Valve:

An air filtration pressure-reducing valve is an accessory in industrial automation instruments. Its primary function is to filter and purify compressed air from the air compressor and stabilize the pressure at the required value. It can be used as the air supply source and pressure stabilizing device for all kinds of pneumatic instruments, solenoid valves, cylinders, spraying equipment and small pneumatic tools.  

Self-locking valve (position preserving valve):

A self-locking valve is a device to keep the valve in position. Pneumatic control valve when the gas source failure occurs, the machine can cut off the gas source signal so that the membrane chamber or cylinder pressure signal to maintain a moment before the failure of the state, so that the valve position is also maintained in the position before the failure, to play the role of position preservation. 

Valve position transmitter:

When the control valve is away from the control room, in order not to the scene to accurately understand the valve switching position, we must be equipped with a valve position transmitter, that is, the valve opening the amount of institutional displacement, according to a specific law converted into electrical signals sent to the control room, this signal can be reflected in the valve of any opening of the continuous movement can also be considered as the inverse action of the valve positioner.    

Travel switch (return signal):

The travel switch reflects the two extreme positions of the valve switch, and at the same time, sends the indication signal device. Based on this signal, the control room can rebel against the valve switch status to take appropriate measures.

Control Valve Arrangement:

The image below shows how a control valve can be used to control rate of flow in a line. The "controller" receives the pressure signals, compares them with pressure drop for the desired flow and if the actual flow is different, adjusts the control valve to increase or decrease the flow.

Comparable arrangements can be devised to control any of numerous process variables. Temperature, pressure, level and flow rate are the most common controlled variables.