1. Why the double-sealed valve cannot be used as a shut-off valve
The advantage of the double-seat valve core 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 compulsorily used for cutting off occasions, the effect is obviously not good. Even if many improvements (such as double-sealed sleeve valve) are made for it, it is not desirable.
2. Why is the double seat valve easy to oscillate when working at a small opening
For single core, when the medium is flow open type, the valve stability is good; when the medium is 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, the flow-closed spool is likely to cause valve vibration when working at a small opening. This is a double seat valve The reason why it cannot be used for small opening work.
3. What kind of straight-stroke regulating valve has poor anti-blocking performance, and angular-stroke valve has good anti-blocking performance
The straight-stroke valve spool is throttling vertically, and the medium flows in and out horizontally, the flow path in the valve cavity will inevitably turn and turn, which makes the flow path of the valve quite complicated (the shape is like an inverted "S" shape). In this way, there are many dead zones, providing space for the precipitation of the medium, and if things go on like this, it will cause blockage. The direction of throttling of the quarter-turn 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 the space for medium precipitation is small, so the quarter-turn valve has good anti-blocking performance.
4.Why the sleeve valve instead of the single and double seat valve did not get what you wanted
The sleeve valve that came out in the 1960s was widely used at home and abroad in the 1970s. In the petrochemical plants introduced in the 1980s, sleeve valves accounted for a larger proportion. At that time, many people believed that sleeve valves could replace single and double valves. The seat valve became the second generation product. Until now, this is not the case. Single-seat valves, double-seat valves, and sleeve valves are all used equally. This is because the sleeve valve only improves the throttling form, stability and maintenance better than the single seat valve, but its weight, anti-blocking and leakage indicators are consistent with the single and double seat valves, how can it replace the single and double seat valves What? Therefore, they can only be used together.