The introduction of the main accessories of the regulating valve

The introduction of the main accessories of the regulating valve

Tianjin Tanggu Water-Seal Valve Co., Ltd (TWS Valve Co., Ltd)

Tianjin，CHINA

22th，July，2023

Web: www.tws-valve.com

Valve positioner is a primary accessory for pneumatic actuators. It is used in conjunction with pneumatic actuators to improve the positioning accuracy of valves and overcome the effects of stem friction and unbalanced forces from the medium, ensuring that the valve is accurately positioned according to the signals from the controller.

The positioner should be used in the following situations:

When the medium pressure is high and there is a large pressure differential.

When the valve size is large (DN > 100).

In high-temperature or low-temperature control valves.

When there is a need to increase the actuation speed of the control valve.

When using standard signals and operating non-standard spring ranges (springs outside the range of 20-100KPa).

When used for staged control.

When achieving reverse valve action (e.g., switching between air-closed and air-opened).

When there is a need to change the flow characteristics of the valve (the positioner cam can be adjusted).

When there is no spring actuator or piston actuator and proportional action is required.

When operating pneumatic actuators with electrical signals, an electrical-air valve positioner must be used.

Solenoid Valve:

When the system requires program control or on-off control, solenoid valves are used. When selecting a solenoid valve, apart from considering AC or DC power supply, voltage, and frequency, attention must be paid to the functional relationship between the solenoid valve and the control valve. It can be either normally open or normally closed type. If it is necessary to increase the capacity of the solenoid valve to shorten the response 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 power amplifier that can transmit pneumatic signals to remote locations, eliminating the lag caused by long signal pipelines. It is mainly used between field transmitters and central control rooms for regulating instruments, or between controllers and field control valves. It also has the function of amplifying or reducing signals.

Converter:

Converters are divided into pneumatic-electric converters and electric-pneumatic converters. Their function is to convert between pneumatic and electric signals according to a certain relationship. They are mainly used when operating pneumatic actuators with electrical signals, converting 0-10mA or 4-20mA electrical signals to 0-100KPa pneumatic signals or vice versa, converting 0-10mA or 4-20mA electrical signals.

Air Filter Regulator:

Air filter regulators are accessories used in industrial automation instruments. Their main function is to filter and purify compressed air from air compressors and stabilize the pressure at the required value. They can be used as gas sources and pressure stabilizing devices for various pneumatic instruments, solenoid valves, cylinders, spray equipment, and small pneumatic tools.

Self-locking Valve (Position Lock Valve):

The self-locking valve is a device used to maintain the valve position. When a pneumatic control valve experiences a failure in the air supply, this device can cut off the air signal, keeping the pressure signal in the diaphragm chamber or cylinder at the state just before the failure. This ensures that the valve position is maintained at the position before the failure, serving the purpose of position locking.

Valve Position Transmitter:

When the control valve is far from the control room and it is necessary to accurately know the valve position without going to the field, a valve position transmitter should be installed. It converts the displacement of the valve opening mechanism into an electrical signal according to a certain rule and sends it to the control room. This signal can be a continuous signal reflecting any valve opening, or it can be considered as the inverse action of the valve positioner.

Travel Switch (Position Feedback Device):

The travel switch reflects the two extreme positions of the valve and simultaneously sends out an indication signal. The control room can determine the valve’s on-off status based on this signal and take corresponding measures.

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