How to determine torque of gate valve?

2021-11-15

How to control the torque of gate valve? Below, we come together to understand it!

◆ When the opening of the gate valve is above 10%, the axial force of the gate valve, that is, the operating torque of the gate valve does not change much. When the opening of the gate valve is below 10%, the pressure difference between front and rear of the gate valve increases due to the throttling of the fluid. This pressure difference acts on the gate, so that the stem requires a large axial force to drive the gate, so the operating torque of the gate valve varies greatly within this range. Flexible gate valves require greater operating torque near closing than rigid gate valves.

◆ When the gate is closed, there will be different conditions due to the different sealing ways of the sealing surface. For automatic sealing gate valves (including flat gate valves), when the valve is closed, the sealing face of the gate is exactly opposite to the sealing face of the seat, that is, the fully open position of the gate valve. However, this position can not be monitored under the operating conditions of the gate valve, so in actual use, the position of the gate valve is closed to the TDC as the fully closed position of the gate valve. It can be seen that the full closing position of the automatic sealing gate valve is determined by the position of the gate (i.e. the stroke). For force-sealed gate valves, the gate must be closed with pressure on the seat. This pressure ensures that the sealing surface between the gate and seat is tightly sealed, and is a mandatory sealing force of the gate valve. This sealing force will continue due to stem nut self-locking. Obviously, in order to provide sealing force to the gate, the stem nut transfers greater torque than during valve operation. Thus, for forcibly sealed gate valves, the full closing position is determined by the torque applied to the stem nut.

◆ After the gate valve is closed, due to the change of medium or ambient temperature, the thermal expansion of the gate valve components will make the pressure between the gate and the valve seat become larger, which will be reflected on the stem nut, which will bring difficulties to the gate valve. Therefore, the torque required to open the gate valve is larger than the torque required to close the gate valve. In addition, for a pair of contacting sealing surfaces, the coefficient of static friction between them is also larger than the coefficient of dynamic friction. In order to make them move relative to each other from the static state, a larger force should be applied to overcome the static friction force. As the temperature changes, the pressure between the sealing surfaces increases, so does the static friction force to be overcome. As a result, when opening the gate valve, the torque applied to the stem nut sometimes increases greatly.

Gate valve torque reference table

Nominal diameter (mm) Nominal pressure (MPa)

0.25 0.6 1.0 1.6 2.5 4.0 6.4 10.0 16.0 20.0 32.0

The moment (N, m)

50 25 25 50 50 100 100 200 200 200 200

65 25 50 50 50 100 200 200 300 450 600

80 50 50 50 80 100 200 200 300 450 600 900

100 50 50 100 200 200 300 300 450 600 1000 1200

125 50 50 200 200 300 300 450 500 900 --

150 50 100 200 300 300 450 500 600 1000 --

200 100 200 300 300 450 500 600 1000 1200 1800 -

250 100 200 300 450 600 600 1000 1200-2500 -