Gate Valve Actuator Sizing

[na5rc]

I am interested in a force that might not normally be considered in actuator sizing for Gave Valves. Normally considered forces are stem friction, seat friction, and hydrostatic. However, it seems there is another force that could be significant under some circumstances, e.g. a higher viscosity, and a high velocity in the pipe. I call it a hydrodynamic force that would vary from open to closed and vice versa.

How can I calculate this hydrodynamic force of pushing a gate into a very fast moving stream (excluding the forces stated above)? It seems that viscosity, velocity, and Reynolds number are key to this value. With regard to velocity, my question would involve an open ended pipe just downstream of the gate valve with plenty of flowing pressure and volume upstream of the valve.

 

[LittleInch]

I think the only relevant effect is pressure difference across the gate which is always less that it is if there is full differential across the valve. Therefore if your actuator can open under full DP, then it will close under flowing conditions.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[na5rc]

I am not trying to size an actuator - I have that info. I need the force required to shear a fast moving stream.

 

[LittleInch]

Then I don't understand what you want. Any effect will be dwarfed by the friction of the gate against the seats caused by the pressure difference which starts to occur as you close the valve. You can calculate this by looking at the valve CV versus percent open graph, but how you then calculate the force on the stem to close the valve further will vary valve by valve.

I would be interested to see if there is such a force, but if so I've never come across it for a gate valve.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[na5rc]

Under normal flow I would agree that this force would be negligible, but imagine a flow at the maximum possible velocity in a pipe. It seems intuitive that the required shearing force increases and could be significant for at least part of the travel.

I actually do have an application and reason for asking this question but I need some definitive info before I can proceed to resolve the issue. If this force is negligible for all process conditions then great - no problem. If not negligible then it is a significant problem that would require entirely different valve types and actuators. The existing actuator force can not be increased.