Holes for safety of valves in wedge (gatevalve) and ball (ball valves)

[kprakash]

Can any body tell me the side of valve (upstream or downstream of flow) for the hole to be drilled on wedge(in case of gate valves) or ball(incase of ball valves) of cryogenic valves for safety.
What is the logic for selecting the side of hole drilled before installation?

regards
prakash kamath prakash kamath

 

[jonralph]

I can only comment on ball valves. Hole faces upstream. Theory being that if it is facing upstream the pressure acts on the inside of the ball and will increase sealing forces. Other way round tends to lead to more leaks (in our experience)

 

How do you calculate sealing forces by ball valves?
Student

 

[pmarriott]

In the case of ball valves the body cavity is normally vented to the upstream side. Therefore, when the valve is in either the open or closed position the cavity will never become excessively pressurised. Venting downstream could give rise to safety issues if downstream piping is dismantled.
Drilling of wedges on gate valves is an unusual practice and would ensure that positive shut-off could not be achieved. I presume this might be done if you needed to provide constant but limited flow through the piping system.

 

[kprakash]

thankyou for the information
These are as per SHELL standards
as you have said the hole side is upstream except for pump,psv discharge where it is on downstream side.
thanks
regards
prakash kamath prakash kamath