Valve leakage problem seriously threatens the normal operation of the device, and the operation of the valve is very difficult to find out whether there is an internal leakage, the results of the survey show that the petrochemical companies use a variety of valves to varying degrees of internal leakage problems. The reason is that the valve plate, valve seat sealing surface material does not meet the requirements of use, processing accuracy is not enough, gate valve valve plate, valve seat wedge angle does not match the sealing surface width is not the same as the degree of coincidence is poor, the gate is not in place, not closed and other factors.
  
  Such as for Z41Y-25, the sealing surface material code Y should refer to the sealing side of the sealing surface material of relatively soft hardness, corresponding to another sealing surface material should obviously be at least cemented carbide, but in fact there are valves only in one of the sealing surface surfacing cemented carbide, while the other sealing surface is a carbon steel body material, put into use after a long time due to wear and tear of the phenomenon of internal leakage.
  
  Another example of a pipeline system selected the clamped butterfly valve, valve seat sealing material using PTFE. From the point of view of the use of working conditions, the requirements are not high, are at room temperature and pressure, but in the trial run found that a number of valves are not closed tightly, the internal leakage is serious, so that it can not be used normally, and then had to be replaced by a gate valve. Remove the inspection found that the valve plate in the closed state and the valve seat has a large gap, and even through the light.
  
  Analyze the reasons may be the following! Valve sealing sub-structure design is unreasonable or manufacturing and assembly accuracy does not meet the requirements; valve installation is not in accordance with the requirements of the construction and make it to withstand excessive force; construction process of welding slag, sand, metal shavings and other impurities into the valve cavity, so that the sealing effect is affected. In fact, more practical, but also the more fundamental reason is in the manufacture, transportation or installation of a process not in accordance with the standard requirements to do.