opening/closing of valve in HP service
opening/closing of valve in HP service
(OP)
Could it be problemmatic to operate the valve (ballvalve)when the pressure is shut in the system either side of the valve of if shut in only one side. I mean would this affect the movement of the ball.
We have a liquid service operating at 1500Lb rating
Does it require a bleed drain in the system to depressurize the systm in some circumstances.???????????
Would be gratful for any advice
We have a liquid service operating at 1500Lb rating
Does it require a bleed drain in the system to depressurize the systm in some circumstances.???????????
Would be gratful for any advice





RE: opening/closing of valve in HP service
If automated, the actuator needs to be large enough to open and close the valve with full differential pressue. The piping system needs to accommodate the hammer from opening and closing the valve.
Many large gas applications use a pressuring valve across a main block valve. Perhaps this would not apply to liquid. Drains are a normal thing in the piping system.
John
RE: opening/closing of valve in HP service
The bleed on gas main valves is to avoid the valve freezing as it is closed or opened and the gas expands on one side.
You might need to depressurise the system to change the valve.
RE: opening/closing of valve in HP service
RE: opening/closing of valve in HP service
Let me explain, if you have full line pressure (1500psig) on one side of the ball, slab gate, or expanding gate and 0psig on the other side, the pressure actually forces the ball, gate, etc. toward the seat on the low pressure side, this is what cause the valve to contain pressure or product. Vavles are actually designed to work off of differential pressure. If the pressure is high enough the friction can get so great between the seat and the ball that it can be hard to operate. Now, if you have some way to equalize the pressure around the valve the friction will decrease and the valve will be eastier to open. I hope that made sense.
In the situation you described, you shouldn't have a problem if you have some sort of equalization around the trap valve. In most cases you are going to want to equalize the pressure in the pig launcher/recever prior to launching the pig. If you don't, you can actually cause th pig to "burp" back up into the l/r rather then send it down the line.
Hope that helps.
ODEM