The Globe Valve is one of the important links in the automated control process instrumentation. The correct selection is crucial to the normal operation of the system. In addition to the pressure, temperature, diameter, material and regulating valve structure and other common parameters, the selection of the Globe Valve needs to be implemented. , also pay attention to the relevant accessories. The main accessories of the Globe Valve include: valve positioner, Solenoid Valve, valve position feedback, air filter Pressure Reducing Valve, position retaining valve, pneumatic relay, etc. The selection of the main accessories is described below. in principle:
1. Valve positioner
The valve positioner is the main accessory of the pneumatic actuator. It is used in conjunction with the pneumatic actuator to improve the position accuracy of the valve and overcome the influence of
Valve Stem friction and medium unbalanced force, thereby ensuring that the valve is realized according to the signal from the regulator. Correct positioning. The valve positioner is used to convert the 4-20mA control signal into a pneumatic signal to the pneumatic actuator, thereby driving the regulating valve to perform the regulating function. Valve positioners are divided into mechanical positioners and intelligent positioners. Intelligent positioners have higher control accuracy and lower air consumption than mechanical positioners. In addition, they can also have HART protocol functions.
2. Solenoid valve
When the system needs to realize program control or two-position control, it needs to be equipped with a solenoid valve. When selecting a solenoid valve, in addition to considering the AC and DC power supplies, voltage and frequency, you must also pay attention to the relationship between the solenoid valve and the regulating valve's action type. It can be equipped with "normally open type" or "normally closed type".
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.
3. Pneumatic relay
Pneumatic relay is a power amplifier that can send air pressure signals to distant places to eliminate the lag caused by lengthened signal pipelines. It is mainly used between on-site transmitters and regulating instruments in the central control room. Or between the regulator and the field
Control Valve, another function is to amplify or reduce the signal.
4. Converter
The converter is divided into a gas-to-electric converter and an electric-to-gas converter. Its function is to realize a certain relationship between gas and electric signals and convert them into each other. It is mainly used to convert 0~10mA or 4~ when using electric signals to operate pneumatic actuators. Convert 20mA electrical signal or 0~100KPa gas signal into 0~10mA or 4~20mA electrical signal.
5. Air filter pressure reducing valve
The 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 for various pneumatic instruments and solenoid valves. , air supply sources and pressure stabilizing devices for cylinders, spraying equipment and small pneumatic tools.
6. Self-locking valve (position-keeping valve)
Self-locking valve is a device that maintains the valve position. When the air source fails, the Globe Valve can cut off the air source signal to keep the pressure signal in the membrane chamber or cylinder at the moment before the failure, so that the valve position is also maintained at the position before the failure. Position-keeping effect.
7. Valve position transmitter
When the regulating valve is far away from the control room, in order to accurately understand the switching position of the valve without going to the scene, it is necessary to equip a valve position transmitter, which converts the mechanical displacement of the valve opening into an electrical signal according to a certain rule and sends it to the control room. The 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.
8. Travel switch (reply device)
The stroke switch reflects the two extreme positions of the valve switch and sends out an indication signal at the same time. Based on this signal, the control room can detect the switching status of the valve so as to take corresponding measures.
