Introduction to regulating valve accessories

Introduction to regulating valve accessories

The regulating valve positioner is the main accessory of the pneumatic actuator. It is used together with the pneumatic actuator to improve the position accuracy of the valve, overcome the influence of valve rod friction and medium unbalanced force, and ensure the correct positioning of the valve according to the signal from the regulator.

Positioner shall be provided in the following cases:

When the medium pressure is high and the pressure difference is large;

When the diameter of the regulating valve is large (dn>100);

High or low temperature control valve;

When the action speed of the regulating valve needs to be increased;

When the actuator of non-standard spring is operated with standard signal (spring range beyond 20 ~ 100KPA);

For split range control;

When the valve operates in the reverse direction (air closing and air opening are mutually switched);

When the flow characteristic of the valve needs to be changed (the positioner cam can be changed);

There is no spring actuator or piston actuator, and proportional action is required;

When operating the pneumatic actuator with electric signal, the power supply - pneumatic valve positioner must be distributed.

Solenoid valve: 

when the system needs to realize program control or two position control, it needs to be equipped with solenoid valve. When selecting solenoid valve, besides AC and DC power supply, voltage and frequency, attention must be paid to the relationship between the action type of solenoid valve and regulating valve, and "normally open" or "normally closed" type can be used. If it is required to increase the capacity of the solenoid valve to shorten the action time, two solenoid valves can be used in parallel or the solenoid valve can be used as a pilot valve in combination with a large capacity pneumatic relay.

Pneumatic relay:

Pneumatic relay is a kind of power amplifier, which can send the air pressure signal to a far place to eliminate the lag caused by the lengthening of the signal pipeline. It is mainly used between the field transmitter and the regulating instrument in the central control room, or between the regulator and the field regulating valve. Another function is to amplify or reduce the signal.

converter:

The converter is divided into pneumatic electric converter and electric pneumatic converter. Its function is to realize the mutual conversion of certain relationship between pneumatic and electric signals. It is mainly used to convert 0 ~ 10mA or 4 ~ 20mA electric signals or 0 ~ 100KPA pneumatic signals into 0 ~ 10mA or 4 ~ 20mA electric signals when operating the pneumatic actuator with electric signals.

Air filter pressure reducing valve:

The air filter pressure reducing valve is an accessory of industrial automation instruments. Its main function is to filter and purify the 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 various pneumatic instruments, solenoid valves, cylinders, spraying equipment and small pneumatic tools.

Self locking valve (holding valve):

The self-locking valve is a device for maintaining the valve position. When the air source of the pneumatic control valve fails, the device can cut off the air source signal to keep the pressure signal of the membrane chamber or cylinder in the state immediately before the failure, so as to maintain the valve position at the position before the failure and play the role of position preservation.

Valve position transmitter：

When the control valve is far away from the control room, in order to accurately understand the opening and closing position of the valve without going to the site, a valve position transmitter shall be equipped, that is, the displacement of the mechanism of the valve opening shall be converted into an electrical signal according to a certain law and sent to the control room. This signal can be a continuous signal reflecting any opening of the valve or a reverse action of the valve positioner.

Travel switch (annunciator)：

The travel switch is a device that reflects the two extreme positions of the valve switch and sends an indication signal at the same time. According to this signal, the control room can turn off the switch state of the valve so as to take corresponding measures.