Solutions to difficult opening and closing of large-caliber valves

1. Analysis of the reasons for the difficulty of opening and closing large diameter valves:

The ultimate horizontal output power of a general adult is 60-90kg, depending on different physiques.

Generally, the flow direction of the shut-off valve is designed to be low in and high out. When a person closes the valve, the human body pushes the handwheel horizontally to move the valve disc downwards to achieve closing. At this time, a combination of three forces needs to be overcome, namely :

1) Axial thrust Fa;

2) Friction between packing and valve stem Fb;

3) The friction force Fc of the contact between the valve stem and the valve core

The total torque is ∑M=(Fa+Fb+Fc)R

It can be seen that the larger the outlet diameter, the greater the axial thrust force. When it is close to the closed state, the axial thrust force is almost close to the actual pressure of the pipe network (because P1-P2≈P1, P2=0 when closed)

For example, if a DN200 stop valve is used on a 10bar steam pipe, only the first item closes the axial thrust Fa=10×πr2=3140kg