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2, two-seat control valve can not be used as a shut-off valve
The valve core of the two-seat control valve has the advantage of the force balance structure, allowing the pressure difference range before and after the valve to be large. Since the two sealing surfaces cannot be in good contact at the same time, the leakage amount is large and cannot be cut off in the pipeline. Even if the sleeve improvement is now added to the double seat valve, it cannot change the limitations caused by the structural design.
3. Comparison of anti-blocking performance between straight stroke regulating valve and angular stroke valve
The spool of the straight stroke regulating valve is vertical movement, the fluid is horizontally moving, and the flow passage structure in the valve chamber is not straight-through, generally S-shaped, which forms a lot of blind spots. Over time, the medium is easy to form in these blind areas. Precipitation, which in turn easily causes clogging. The spool of the angular stroke valve is in a horizontal rotary motion, and the medium is also in a horizontal flow direction, so that there is no easy dead angle and the deposited material is easily carried away by the fluid. Therefore, the straight stroke regulating valve is much better than the anti-blocking performance of the angular stroke valve.
4, the reason for the straight valve of the straight stroke regulating valve
Due to the large sliding friction and small rolling friction. The valve stem of the straight stroke valve is made to slide up and down, which produces a large friction. Therefore, the valve stem is designed to be small, and the PTFE filler with a small friction coefficient is used for the purpose of reducing the friction. However, there is a problem that the valve stem is thin, the bending is easy, and the life of the filler is short.
5, the angular stroke valve has a large cutoff pressure difference
Since the resultant force generated by the medium on the valve core has a very small torque to the valve shaft, it can withstand a large pressure difference, so the cut-off pressure difference of the angular stroke type valve is large.
6. Why should the shut-off valve be hard-sealed as much as possible?
Soft- sealed valves perform better than hard-sealed valves only in terms of cutting effect. However, the soft seal valve has much better wear resistance and reliability than the hard seal valve. Therefore, from the double standard of leakage and reliability, the hard seal shut-off valve is better than the soft seal cut-off valve. Many cutting valves now use surfacing and wear-resistant alloys to greatly improve the sealing performance, which is enough to meet the requirements of the shut-off valve.
Several frequently encountered problems with regulating valves
1. The two-seat control valve is easy to oscillate when it is in a small opening working condition.
Why is the two-seat control valve not available for small opening, which is determined by its seat structure. The double regulating valve has two spools, the upper spool is open, the lower spool is closed, and the spool of the regulating valve is flowing, the stability is better, so when the spool of the double seat regulating valve is close to the flow When the small opening range of the closed state is working, the spool will oscillate. Therefore, in the selection of the regulating valve, it is necessary to avoid the use of the two-seat regulating valve in the small opening range.