Valve common questions 5 questions 5 answers

1. Why is the two-seat valve easy to oscillate when working with small opening?

For a single core, when the medium is flow open, the valve stability is good; When the medium is flow closed type, the stability of the valve is poor. The double-seat valve has two spool, the lower spool is in the flow closed, the upper spool is in the flow open, so that when the small opening is working, the flow closed spool is easy to cause the vibration of the valve, which is the reason why the two-seat valve cannot be used for small opening work.

2. Why can't double seal valve be used as a cut-off valve?

The advantage of the two-seat valve spool is that the force balance structure allows the pressure difference to be large, and its outstanding disadvantage is that the two sealing surfaces can not be in good contact at the same time, resulting in large leakage. If it is artificially and forcibly used for cutting occasions, it is obviously not effective, even if many improvements have been made for it (such as double-sealed sleeve valves), it is not advisable.

3. What is the anti-blocking performance of the straight stroke regulating valve poor, and the anti-blocking performance of the Angle stroke valve good?

The spool of the straight stroke valve is a vertical throttling, and the medium is a horizontal flow into and out, and the flow path in the valve chamber must turn and reverse, so that the flow path of the valve becomes quite complex (shape such as inverted "S" type). In this way, there are many dead zones, providing space for the precipitation of the medium, and over time, causing blockage. The direction of the angular stroke valve throttling is the horizontal direction, the medium flows horizontally into and out horizontally, it is easy to take away the unclean medium, and the flow path is simple, and the space for the medium to precipitate is also very little, so the angular stroke valve has good anti-blocking performance.

4. 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 stem of the straight stroke valve moves up and down, and the packing is slightly pressed, it will wrap the valve stem very tightly, resulting in a larger return difference. For this reason, the valve stem is designed to be very small, and the packing is commonly used with a small friction coefficient of tetrafluoroidal packing in order to reduce the return difference, but the problem sent from this is that the valve stem is small, it is easy to bend, and the packing life is short. To solve this problem, the best way is to use the rotary valve stem, that is, the regulating valve of the Angle stroke class, its valve stem is 2 to 3 times thicker than the straight stroke valve stem, and the choice of long life graphite filler, the valve stem stiffness is good, the packing life is long, and the friction torque is small and the return difference is small.

5. Why the Angle stroke valve cut off pressure difference is large?

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