Control of pneumatic valve cavitation and flash preventive < / div >

in pneumatic control valve flow liquid often appears in flash and two phenomena. They occur not only influence the choice of caliber and calculation, and it will lead to serious noise, vibration, the destruction of the material, etc. In this case, the pneumatic control valve of a shorter working life, it is necessary to take in detail. Under normal circumstances, as a liquid medium, flow, flow, flow control pneumatic valve shall remain liquid. Flash as medium of liquid, flow control pneumatic valve is liquid, in through the control of the pneumatic valve flow when fluid pressure is lower than the gasification Pvapor, liquid into a gaseous medium, and its pressure won't return to gasification, keep gas flow control pneumatic valve medium. The pressure change curve as shown in figure 7 ( 2) Shown below.
flash like a sandblast phenomenon, its role in the downstream part of the pneumatic valve and pipeline, to control the inner surface of the pneumatic valve and pipe cause serious erosion, but also reduces the flow capacity of pneumatic control valve.
cavitation as medium of liquid, flow control pneumatic valve is liquid, in through the control of the pneumatic valve flow when fluid pressure is lower than the gasification of liquid medium into a gas medium, then it's pressure and response to the gasification Pvapor, finally in front of the pneumatic flow control valve into a liquid medium. Can preliminary judgment according to some phenomenon of cavitation, when cavitation at the beginning it will emit a hiss, when the development of cavitation completely stable, pneumatic control valve in gaga sound, like a gravel the sound when through the control of pneumatic valve. Cavitation damage to the control of pneumatic valve and internals is also very big, and it also reduces the flow of control pneumatic valve performance, just like flash.
therefore, we must take effective measures to prevent or minimize the flash or the cavitation occurrence:
(1) as far as possible will control pneumatic valve installed in the system of the lowest place, so can relatively improve control pneumatic valve inlet pressure P1 and P2 export, (2) in the control of pneumatic valve upstream or downstream of the pneumatic valve installed a deadline or throttling orifice plate to change the original installation of the pneumatic control valve pressure drop characteristics ( This method is more effective for small flow conditions) in ,
choose a special anti cavitation can also effectively prevent flash or cavitation, it can change the fluid velocity changes within the control of pneumatic valve, thus increasing the internal pressure;
4. Try to choose material harder control pneumatic valve, because at the time of the cavitation for such control pneumatic valve, it has a certain resistance to erosion and abrasion resistance, can let the cavitation under certain conditions, and will not damage control pneumatic valve internal parts. For soft material, on the other hand, the pneumatic control valve, due to its poor resistance to erosion and abrasion resistance, when cavitation occurs, the control of the pneumatic valve internals will soon be wear and tear, and therefore unable to work in the case of wind erosion.
all in all, there is nothing under the condition of engineering materials can adapt to severe cavitation condition, can only be comprehensive analysis in view of the objective conditions, choose a relatively reasonable solution.