Principle of Vpr pneumatic valve and maintenance of five faults of positioner


PR pneumatic valve positioner (Vpr positioner for short) is a special accessory of VFR cam flexure control valve of Yamato Honeywell company. According to the signal of the pneumatic regulator, it makes the regulating valve act correctly and quickly, so as to accurately regulate the valve flow and ensure the flow characteristics. Our factory was introduced into production in the mid-1980s, and has been widely used in the automatic control system of petrochemical, electric power, light industry and chemical industry.

In order to use and maintain correctly, it is necessary to explain its working principle. When the input signal increases, the bellows expand to push the baffle (i.e. lever) * near the nozzle end face. When the gap decreases, the back pressure of the nozzle increases, and the spool is pushed down by the diaphragm of the relay. The output pressure increases when the air inlet is opened and the exhaust port is closed. Therefore, the actuator push rod moves downward to open or close the valve core of the regulating valve. As the valve core rotates, the cam also rotates. The feedback spring is pulled by the cam follower to make the baffle tend to leave the nozzle until the torque generated by the bellows is balanced with the torque of the feedback spring. Due to the correct relationship between the valve core and the valve opening, the valve core can be adjusted accurately

The following analysis of common fault causes and measures. Simple exclusion measures will be omitted.

No output pressure of positioner

1. There is no signal pressure, ① the pneumatic regulator fails; ② the signal pipeline leaks a lot.

2. If the bellows leaks a lot, solder or replace it

3. There is no air supply pressure or the air supply pressure is too low.

4. The orifice of bellows is blocked, and metal wire with diameter less than 0.2mm is used for dredging.

5. The zero position of positioner is not adjusted properly, that is, the gap between baffle and nozzle is too large. Use the tool to readjust.

6. The installation position of cam is wrong. Because a cam contains air to open and air to close equal percentage; air to open and air to close linear characteristics, there are four mounting holes, easy to install wrong.

7. The baffle plate is not perpendicular to the nozzle end face, and there is still a large amount of exhaust gas after the baffle plate contacts with the nozzle end face.

8. There are pits on the end surface of nozzle hole, which needs to be replaced. If there is burr on the end face, grind it again.

9. There is air leakage at the joint between nozzle and base.