Pressure Relief

Valves are installed backwards?

Gage is faulty.

Can you draw and post a sketch?

Is it due to elevations and/or friction head losses?

What is the liquid?

1) The flow of the fluid may be too large with ref to the capacity of the relief valves. (thus there is a pressure frop in the relief valve orifice) More prominent when the fluid is viscous by itself or the temperature is low. In one of our Hyd circuit during testing i have seen the relief valve tripping at 8 bar and when the outlet is blocked off (a part of our testing), the pressure going up to about 10-11 bar (but never double)

2) Check the setting of the relief valve - in case of sub standard valves (esp spring) the settings sometimes get disturbed.

3) Is the line OK ? What is the length of line ? where are the valves with ref to the pump and gauge.

4) Check the line back to tank, it should be as free as possible, no reducers and no air entrapment possibilities in brief the fluid resistance of the relief valve outlet should be as low as possible with ref to the quantity of fluid it is expected to carry under worst circumstances (that is mandatorily equal to pump capacity if the pump do not have a inbuilt relief)

Doubling of the pressure is quite abnormal check the relief valve setting and the relief valve to tank connection/

I am assuming the relief valve is immediately after the pump (before filter) and the pressure sensor/gauge is nearby

Steady state or dynamic?

Water hammer?

check any directional valves / check valves. Match components to service - gas components in a fluid system?

How long has this system been in service? Have any mods or repairs been made recently?

It's called waterhammer. The moving water can cause a pressure rise locally in a flowing pipe due to the inerta effects of the flowing water suddenly stopping, like when a valve is closed. Could this be it?

I hope this guy/gal writes back with more information...

Why do you have 3 RVs protecting 1 liquid line? Are they for progressive vaporization relief? Pressure losses in a liquid system can get pretty high quick, especially if the line is undersized and you are trying to push an elephant through the eye of a needle. This can get you in a high velocity situation quickly and you can do some real damage to a system with some righteous water hammer.

The line is used for petro products. We install pressure relief around evrey valve to ensure the product line(pipe)does not rupture, in the event someone closes the valve. At the dock there is a valve, as the product goes to or comes from tanks there are valves to direct the flow. Every valve gets a relief.