1、 Why can’t the double seal valve be used as a shut-off valve?
The advantage of the two seat valve core is the force balance structure, which allows a large differential pressure. However, its prominent disadvantage is that the two sealing surfaces cannot be in good contact at the same time, resulting in large leakage. If it is artificially and forcibly used in cutting off occasions, the effect is obviously not good. Even if many improvements have been made for it (such as double seal sleeve valve), it is not desirable.
2、 Why is the double seat valve easy to oscillate when working with a small opening?
For single core, when the medium is flow open type, the valve has good stability; When the medium is flow closed, the stability of the valve is poor. The double seat valve has two valve cores, the lower valve core is in the flow closed position and the upper valve core is in the flow open position. In this way, the flow closed valve core is easy to cause valve vibration when working with a small opening, which is the reason why the double seat valve cannot be used for working with a small opening.
3、 What is the poor anti blocking performance of the straight stroke control valve and the good anti blocking performance of the angular stroke valve?
The valve core of the straight stroke valve is vertical throttling, and the medium flows in and out horizontally. The flow channel in the valve chamber must turn and turn, making the flow path of the valve very complex (such as the inverted s shape). In this way, there are many dead zones, which provide space for the sedimentation of the medium. In the long run, it will cause blockage. The throttling direction of the angle travel valve is the horizontal direction. The medium flows in and out horizontally, which is easy to take away the dirty medium. At the same time, the flow path is simple, and there is little space for medium sedimentation, so the angle travel valve has good anti blocking performance.
4、 Why is the cut-off pressure difference of angle stroke valves large?
The cut-off pressure difference of angle stroke valve is large because the resultant force generated by the medium on the valve core or valve plate has a very small torque on the rotating shaft, so it can withstand a large pressure difference.
5、 Why is the stem of the straight stroke regulating valve thinner?
It involves a simple mechanical principle: large sliding friction and small rolling friction. The valve rod of the straight travel valve moves up and down, and the packing is slightly compressed, which will wrap the valve rod tightly, resulting in large return difference. For this reason, the valve rod is designed to be very small, and the PTFE packing with small friction coefficient is often used as the packing to reduce the return difference. However, the problem is that the valve rod is thin, it is easy to bend, and the service life of the packing is also short. The best way to solve this problem is to use the travel valve stem, that is, the angle stroke regulating valve. Its stem is 2 ~ 3 times thicker than the straight stroke stem, and graphite packing with long service life is selected. The valve stem has good rigidity, the packing has long service life, and its friction torque is small and the return difference is small.
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