The valve housing is typically machined from castings. Although forgings can be used in place of castings for high temperature and high pressure applications, large size housings are typically manufactured from castings due to process or cost constraints. Due to the existence of a large number of defects such as pores, slag inclusions, cracks, shrinkage and looseness in the castings, these defects are exposed at any time during the operation of the valve, posing a hidden danger to the safe operation. Another reason is that the stem surface is corroded by the media due to improper handling or material selection or the filler fails to corrode the stem sealing surface. The up and down movement of the valve stem will bring out the filler particles from the surface rust. Repeatedly, the gap of the packing gap will occur. If the maintenance is not proper, the high pressure or high speed medium will punch out the packing in a very short time to form a leak. Similarly, a high-pressure self-tightening valve with a graphite stainless steel wire wound material as a seal and a medium flange sealing valve with a stainless steel graphite wound gasket should also prevent such occurrences. Another reason also often causes a large amount of leakage of the medium, that is, the gap between the packing gland and the valve stem is too large. During the movement of the valve stem up and down, the friction material will be repeatedly rubbed out due to excessive clearance, and finally the packing compression ratio will be finally obtained. The pressure drops, causing a leak.

(2) Gate valve leakage

There are many reasons for the leakage inside the valve. The inner valve leaks and closes when the new valve runs shortly, and the sealing surface should be mixed with foreign matter. Therefore, the newly installed valve products should be carefully inspected before being put into operation, and careful flushing can alleviate such accidents.