1. Why does a double seating valve tend to oscillate at a small opening state?

When it comes to a sing-spool valve, it will have excellent stability when the medium is open-flow type, which means the medium flows towards the direction favorable to the opening of the valve. In contrast, when turn it into close-flow type, the valve’s stability falls. Based on the above, the double seat valve has a bad stability and tends to vibrate at small opening sate, because its two spools--the upper one is in flow-close situation while the lower one is bound to be in flow-open--work simultaneously.

2. Why can’t a double seal valve be used to cut off medium?

Tanks to its force-balanced structure, the double seal valve has a large differential pressure. But the leakage brought by the imperfect contact of the two sealing faces will lead to horrible consequences if it is used as a cut-off valve.

3. Why does a linear motion valve do worse in anti-blocking than rotary motion valve?

The linear motion valve cut off the flow vertically but the medium horizontally flows in and out. The flow path in the cavity, extending in twist and turns, enables the impurities to precipitate in the so-called dead zones. As time goes by, the path will be blocked. On the contrary, the rotary motion valve cut the flow off horizontally and has a relatively simple flow path. Therefore, the rotary motion valve has a better anti-blocking performance.

4.Why the stem of linear motion valve is relatively small

It refers to an easy mechanical principle: high sliding friction brings low rolling friction. The stem of the linear motion valve moves up and down. The packing, which is slightly compressed, will wrap the stem very tightly, resulting in a large backlash. To avoid that, the stem is designed to be very thin and small.

5. Why does rotary motion valve can bear high differential pressure?

That’s because the resultant force that the medium produced on the spool or plate only has a very small torque on the axis of rotation. As a result, the rotary motion valve bears high differential pressure