The regulating valve positioner is the main accessory of the pneumatic actuator, which is used in conjunction with the pneumatic actuator to improve the position accuracy of the valve, overcome the influence of valve stem friction and medium imbalance force, and ensure that the valve is correctly positioned according to the signal from the regulator.
1. When the medium pressure is high and the pressure difference is large;
2. When the diameter of the regulating valve is large (DN>100); 3. High or low temperature regulating valve;
4. When it is necessary to increase the operating speed of the regulating valve;
5. When using standard signals and operating non-standard spring actuators (spring range outside 20-100KPa);
6. When used for split range control;
7. When the valve is operated in reverse (switching between gas closed and gas open);
8. When it is necessary to change the flow characteristics of the valve (the locator cam can be changed);
9. No spring execution
When the mechanism or piston actuator needs to achieve proportional action;
10. When using electrical signals to operate pneumatic actuators, it is necessary to use an electrical valve positioner.
Solenoid valve:
When the system needs to implement program control or two position control, an electromagnetic valve is required. When selecting solenoid valves, in addition to considering AC and DC power sources, voltage, and frequency, attention must be paid to the relationship between the type of action of the solenoid valve and the regulating valve. "Normally open" or "normally closed" types 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 combined with a large capacity pneumatic relay as a pilot valve.
Pneumatic relay:
Pneumatic relay is a power amplifier that can send air pressure signals to distant places, eliminating hysteresis caused by extended signal pipelines. It is mainly used between field transmitters and regulating instruments in the central control room, or between regulators and field regulating valves. Another function is to amplify or reduce signals.
converter:
Transformers are divided into gas electric converters and electric gas converters, whose function is to achieve a certain relationship between gas and electrical signals and convert them into each other. They are mainly used to convert 0-10mA or 4-20mA electrical signals or 0-100KPa gas signals into 0-10mA or 4-20mA electrical signals when operating pneumatic actuators with electrical signals.
Air filter pressure reducing valve:
Air filter pressure reducing valve is an accessory in 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 a gas supply source and stabilizing device for various pneumatic instruments, solenoid valves, cylinders, spraying equipment, and small pneumatic tools.
Self locking valve (retaining valve):
A self-locking valve is a device that maintains the valve position. When the air source fails, the pneumatic control valve can cut off the air source signal, keeping the pressure signal of the diaphragm chamber or cylinder in the state before the fault, so that the valve position is also maintained at the position before the fault, playing a protective role.
Valve position transmitter:
When the regulating valve is far away from the control room, in order to accurately understand the position of the valve switch without going to the site, a valve position transmitter should be equipped, which 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 opening of the valve, or it can be considered as the reverse action of the valve positioner.
Travel switch (feedback device):
The travel switch is a device that reflects the two extreme positions of the valve switch and sends out indication signals at the same time. The control room can use this signal to trip the valve switch status in order to take corresponding measures.