Using pneumatic control valve of common questions

When using the pneumatic - valve at ordinary times, we will meet the following questions? When faced with these problems are not considered is what reason, how should solve? Let's discuss the pneumatic - valve a few common problems and solving tips. 1, why double seal valve cannot be used as a cut-off valve? Two-seater valve core has the advantage of force balance double seal valve structure, allow the pressure difference is big, but its disadvantage is that the two seal face not good contact at the same time, cause leakage. If it is used to cut off at artificially, mandatory, obviously the result is bad, even as it made many improvements ( Such as double sealing sleeve valve) It is not desirable. 2, easy oscillation when why small open of the two-seater valve work? For single core, when the medium is away, pneumatic control valve stability is good; When the medium is flow closed type, the stability of the pneumatic control valve will be poor. Two-seater valve has two valve core, the valve core flow closed, valve core in the flow, so that when you are working in a small open degree, flow closed type of valve core is easy to cause the vibration of the valve, this is the reason why two-seat valves cannot be used for small open degree work. 3, why quarter-turn valves to cut off the pressure difference is bigger? Quarter-turn type of valve to cut off the pressure difference is bigger, because the media on the valve core and valve plate produced by the resultant force on the rotating shaft torque is very small, so it can bear large pressure difference. 4 what straight travel, held in pneumatic control valve performance is poor, quarter-turn valves prevent performance is good? Straight travel is vertical throttling valve core and the medium is horizontal, cavity flow is bound to turn down turn, make valve flow becomes quite complex ( Shapes such as' S 'type) 。 In this way, there is a lot of dead zone, provide the space for medium of precipitation, in the long term, causing congestion. Quarter-turn valves throttling direction is horizontal, flow into the medium level, level, easy to take unclean medium, at the same time, simple flow, precipitation medium space is little, so quarter-turn valves prevent performance is good. 5 why straight travel, pneumatic control valve stem is fine? It involves a simple mechanical principle: large sliding friction, rolling friction is small. Straight trip valve stem up and down movement, packing a little pressure, it will wrapped the stem very tight, produce bigger return difference. To this end, the valve stem design very tiny, packing and commonly used small friction coefficient of ptfe packing, in order to reduce the return difference, but the problem is sent stem thin, easy to bend, packing and short service life. Solve this problem, a good way is to travel with rotary valve stem, namely quarter-turn class pneumatic control valve, the valve stem than straight travel stem thick 2 ~ 3 times, and to choose life long graphite packing, good stiffness, the stem packing long life, instead of the friction torque is small, poor little back.