The working principle of pneumatic valves and failure analysis


1 Pneumatic valve principle of operation

The so-called pneumatic valve, specifically refers to the cylinder as an actuator, with compressed air as the power source to achieve the valve drive, in order to achieve the adjustment of the switch. When the regulating pipeline receives the control signal from the automation control system, it will adjust the temperature, pressure, flow and other related parameters. In general, pneumatic valves are characterized by reliability, fast response and simple control. In the specific operation process, the regulating air chamber input 0.02-0.10MPa signal pressure, the film will appear thrust, in the process of thrust disc downward movement will be compressed spring, to achieve the valve stem, push rod and spool downward movement, to achieve the purpose of valve adjustment.

2 pneumatic valve common failures and handling methods

Through the study and analysis of the fault state of pneumatic valves, it is understood that the possible faults are valve jamming, valve inaction, valve leakage and vibration, etc. Therefore, it is necessary to develop countermeasures according to the actual fault, in order to achieve smooth operation of the system and create higher benefits.

2.1 Pneumatic valve jamming

If the action of the valve stem is sluggish, it means that there may be viscous substances in the valve body, and the pneumatic valve jamming mainly occurs in the early operation of the system. When encountering this situation, the valve or subline should be quickly opened and closed to flush away the media blocking the valve. At the same time, you can also use a pipe clamp to clamp the valve stem and apply signal pressure to rotate the valve stem with counter force. If the above problem still cannot be solved, then the drive power can be increased by way of repeated up and down movements. It should be noted that the above operation has a strong professional nature, so in solving and dealing with this fault need to be done with the help of professionals.

2.2 Valve does not move
For this fault, the first step is to determine whether the pressure of the gas source is normal, on this basis to find the gas source fault. When the pressure of the gas source in the valve is normal, it is necessary to determine whether the amplifier of the electric/gas converter has an output. When there is no output, there are two possible situations: first, the air is compressed and placed at the amplifier ball valve; second, the amplifier constant throttle hole is blocked. In this case, it is necessary to clean the air source, remove debris and unclog the constant throttle orifice. If the valve is still inactive after the above treatment, the valve needs to be removed and a full inspection is performed.


2.3 Valve noise
In the fluid flow through the valve, once the front and rear pressure difference is more obvious, then it will cause cavitation phenomenon, cavitation is mainly based on the valve spool and valve seat, which makes the fluid noise. Flow capacity value if the choice is too large, then you need to reset the regulating valve, select and flow capacity value to adapt and match the regulating valve, which can effectively reduce the noise, the following noise elimination methods for the specific introduction and analysis: (1) eliminate resonance noise method. Only in the state of valve resonance can make the energy to overlap, and then produce a hundred decibels of noise. Which performance there is a great difference, some vibration strong, some vibration weak, vibration strong noise is not great, vibration weak, noise is larger; some are vibration and noise are very large. This noise tends to produce a monophonic sound, after the elimination of resonance, the noise will also be reduced; (2) eliminate cavitation noise method. Cavitation as an important part of hydrodynamic noise, for the strength of the noise has a more prominent impact. When cavitation, bubble rupture will invariably produce high-speed impact, which will breed strong local turbulence, cavitation noise is generated. This noise will produce a grating sound, which is very similar to the sound of gravel. Elimination of cavitation can effectively reduce noise; (3) the use of sound-absorbing materials method. Attractive material as a very common sound treatment method, the processing effect played very good. With the help of the attraction material to surround the source of noise, can effectively reduce the noise. Because the noise will spread, and thus the attraction material surrounded by which part, it will eliminate the noise of this part. This way is more used to the noise is not big, the main reason is that this method consumes a lot of money; (4) series of silencer method. Series silencer method is more is applied to the aerodynamic noise muffling, this method can be very good at eliminating noise. For the high mass flow rate of the valve before and after the comparison, it can be clear that the method is very well thought out, not only the effect is better, but also very cheap. With the help of this method the noise decibels can be effectively reduced, but from an economic point of view, the noise reduction is usually limited to 25 decibels.