Valve FAQ

Why can't the double seal valve be used as a shut-off valve?

The advantage of the double seat valve spool is the force balance structure, which allows a large pressure difference, but its outstanding 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 for cutting off occasions, the effect is obviously not good. Even if many improvements are made for it (such as double-sealed sleeve valve), it is not desirable.

Why is the control valve easy to oscillate when the double seat valve is working with a small opening?

For a single core, when the medium is a flow-open type, the valve stability is good; when the medium is a flow-closed type, the valve stability is poor. The double-seat valve has two spools, the lower spool is in flow-closed, and the upper spool is in flow-open. In this way, when working with a small opening, the flow-closed spool is easy to cause valve vibration. This is the double-seat valve. The reason why it cannot be used for small opening work.

What kind of straight stroke regulating valve has poor anti-blocking performance, and angular stroke valve has good anti-blocking performance?

The spool of the straight stroke valve is a vertical throttling, and the medium flows in and out horizontally. The flow path in the valve cavity must turn and turn backwards, which makes the flow path of the valve quite complicated (shaped like an inverted S shape). In this way, there are many dead zones, which provide space for the sedimentation of the medium, which will cause blockage in the long run. The throttling direction of the angle stroke valve is the horizontal direction. The medium flows in horizontally and flows out horizontally, which is easy to take away the unclean medium. At the same time, the flow path is simple and there is little space for the medium to settle, so the anti-blocking performance of the angle stroke valve is good.

Why is the cut-off pressure difference of the quarter-turn valve larger?

The cut-off pressure difference of the angular stroke valve is large because the resultant force generated by the medium on the valve core or the valve plate has a very small torque on the rotating shaft, so it can withstand a large pressure difference.

Why is the straight stroke regulating valve stem thinner?

It involves a simple mechanical principle: high sliding friction and low rolling friction. The valve stem of the straight-stroke valve moves up and down, and the packing is slightly compressed, it will wrap the valve stem tightly, resulting in a large return difference. For this reason, the valve stem is designed to be very small, and the packing is usually made of tetrafluoro packing with a small friction coefficient to reduce the return difference, but the problem is that the valve stem is thin, easy to bend, and the packing life is short. The best way to solve this problem is to use a travel valve stem, that is, an angular travel control valve. Its stem is 2 to 3 times thicker than a straight travel stem, and a long-life graphite packing is used, and the stem stiffness OK, long packing life, what is a hard seal?

The cut-off valve requires the lower the leakage, the better. The leakage of the soft-sealed valve is the lowest. Of course, the cut-off effect is good, but it is not wear-resistant and has poor reliability. From the double standard of small leakage and reliable sealing, soft sealing is not as good as hard sealing. For example, the full-featured ultra-light regulating valve is sealed and piled with wear-resistant alloy protection, with high reliability and a leakage rate of 10 to 7, which can already meet the requirements of shut-off valves.