Gate Valve Stem Axial Load

[Zac H]

Hi,

I am trying to determine the axial (vertical) force that will be experienced by the stem of a gate valve. I know this will comprise the weight of the wedge and shaft, but will there also be a component from the hydrostatic pressure on the closed wedge? When opening the valve from the closed position, would the entire hydrostatic force (which is acting horizontally on the wedge) be taken up in the valve stem? or only a vertical component of it? How would I determine the vertical component?

Any discussion and help on this topic would be greatly appreciated.

Thanks!

 

[LittleInch]

See

https://www.nrc.gov/docs/ML1134/ML11347A383.pdf

The force on a gate valve stem is not easy to determine with any accuracy without testing.

It also varies considerably depending on where it is in the operation. More than 50% open the forces are essentially weight plus stem upwards force as a result of pressure (pressure x stem area).

More than 50% closed to fully closed other forces come into play especially in the last 10% where a pressure drop starts to occur on a moving fluid creating friction between gate and guide / seal and also vertical loads as the gate or disc starts to fully seat.

If this is a wedge gate or double acting split gate then you have other forces as the gate is wedged into a slot or is forced against the seats on either side of the gate.

This is pretty basic stuff here - have you tried to find out data from other sources?

Why do you want to know?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Zac H]

Thanks for the reply, I'll have a read of that resource.

It sounds like I was on the right track and it would be incorrect to ignore the friction on the gate in the seated position. I was just unsure of how to go about calculating this force, but I think it should just be a simple friction calc now.

It's not the easiest application to describe but I'll try. Basically a rather old wedge gate valve is being fitted with a new actuator, but due to space constraints the actuator must be installed on a riser above the valve with an extension spindle connecting to the existing valve stem. Second to this, the thrust bearings in the valve have corroded, and the valve cannot be taken offline to replace the inner thrust bearing. To take load off the failed bearings, we plan to lift the valve stem slightly (a few mm) and instead take up the load in the thrust bearing of the new actuator gearbox. However, the coupling between the new extension shaft and the existing valve stem will need to take both the axial force and torque (worst case would be when unseating the valve I think). My task is to select an appropriate off the shelf coupling or design a custom piece. Therefore I need to work out what the maximum axial force experienced by the coupling is (max torque I can get from gearbox manufacturer).