Why pneumatic valve leakage? What are the reasons

Pneumatic valve if the leak? How to troubleshoot the pneumatic valve? Leakage problems seriously threaten the normal operation, and operation of the valve and it's hard to find whether there is leakage, results show that the existence of the petrochemical enterprise to use different degree of the valve leakage problems. The reasons of disc, seat sealing surface of the material do not conform to the requirements of the use, the machining accuracy is not enough, the valve plate gate valve, the seat of the wedge Angle is not matching, sealing surface width different, alignment, closed tightly and other factors. As for Z41Y - 25, sealing surface material code should be Y refers to seal in the relatively soft sealing surface hardness material, the corresponding also clearly at least another sealing surface material should be cemented carbide, and actually some valve only in one of the overlaying welding carbide seal face, and another seal face material is carbon steel frame, put into use after the time is not long because of the wear phenomenon of leakage. And as a pipeline system chose the wafer butterfly valve, valve seat adopt ptfe sealing materials. From the point of working condition, demand is not high, atmospheric pressure, but found that the number of the valve in the process of commissioning is lax, severe leakage, so can't normal use, and then need to replace the gate valve. Tear open come down to check found that closed the valve plate and valve seat there is a big gap, pervious to light. Analysis of the reason may be the following: the structure of the pneumatic valve seal design is not reasonable or manufacture and assembly accuracy can not meet the requirements; The valve installation failure to construction and make its bear too much force; In the construction process of welding slag, sand, scrap metal, such as impurities into the valve cavity, the sealing function is affected. , is practical, is also the fundamental reason is that in the manufacturing, transportation and installation of a process is not stipulated in the standard requirement to do.