I'm trying to calculate opening/shutting torque values for a rising stem gate valve. The problem is that I can't find coefficients of friction for a monel operating nut on a bronze wear surface. Anyone have ideas for values or references?
Does the valve have a rotary actuator that pushes and pulls the valve stem via a rack-and-pinion or similar device?
I would like to see this valve. I don't know that I've seen a gate valve where the stem friction wasn't due to the interface between the valve stem and the valve packing. Regardless, unless this is a small valve in low pressure service, you're going to find that the packing friction force is substantially less that the process forces.
The valve is just a 10" 300lb. manually operated rising stem gate valve. I agree the largest contributor to stem friction is packing, but I'm looking for a way to reduce the operating nut friction without changing too much existing design (maybe PTFE thrust washers).
Hi,jabsab
In one of our applications we have just used conventional thrust bearing on the stem nut and the result was fantastic.The operating torque has come down drastically.Better try it yourself and you will appreceiate.
jabsab, I agree the largest contributor could be packing - and motion could be improved as others describe above, but the D/P across the gate is often what makes a gate valve stick near the shut position (bypass/pressure equilibration could be needed to nullify sometimes enormous break-free friction forces).