Elevation of PSVs in Plants 1

[shaff]

Hi,

I have observed this in all the site visits I have done. Top most thing in any train of piping is a PSV. It takes the highest elevation above the pipe rack.
What is the logic? I do not want to get into hydraulics of it, but a basic logical reason to quench my curiosity.

Thanks

 

[bljnv]

Safety valves are meant to relieve excess vapor/steam pressure generated in the system. Logically they should be kept at the highest point.

 

[LittleInch]

For a two phase system it needs to be at the top so that it is always in the gas phase for which it will be sized.

For wholly liquid systems this may not apply, but normally mounted at the top so that a) nothing falls in it to block it up (dirt etc), b) If gas does appear and is vented it will relieve this first.

It also tends to make it easier to comply with the requirement for a slope on the vent line away from the valve as required by the codes.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[JSOSA555]

Those valves are also designed to work in vertical position (the spring needs to be that way) It’s a rule!!!, Because the set point of the PRV must be depending only on the force of the spring, if you install it horizontally, also side forces, sliding and friction affects the setpoint (and you can not messure them) . Also the inlet piping must be the shortest possible. In API and ASME standards you can find some guidelines regarding installation, if you install the valve on the side of the pipe, you must use elbows and additional fittings in order to keep the valve in vertical position, so in this scenario de pressure drop at the inlet of the valve will be higher and you can have problems like chattering.

There are valves desgined to work on gas, vapour, liquid or even 2 phases, depends on the system

Hope this could be helpful

 

[pennpiper]

The correct answer is:
Closed system PSV's are mounted at a high point so the outlet line (Downstream Side) will drain free into the Flare system.

Open system PSV's (such as Steam relief valves) are mounted at a high point so the outlet can be easily directed to atmosphere in a safe manner away from work areas.

prognosis: Lead or Lag