Low Press Steam Relief Valve Manifold Sizing

[BronYrAur]

I have four (4) 15 psig boilers, each rated at 4,000 MBH input. How do I size a manifold for the relief lines? They wish to header them together and exit through the roof.

 

[Shmulik]

You may find some assistance at the following:

http://www.spiraxsarco.com/resource...torials/safety-valves/safety-valve-sizing.asp

http://www.chemengsoftware.com/techinfo/headers.htm

http://www.pdhcenter.com/courses/m112/Selection and Sizing of Pressure Relief Valves.pdf

Personally, I don't like the idea of connecting several pressure safety / relieve valves to one header.
You should consider the possibility that some or even all the valves are opened simultaneously. The set pressure of each valve may not be the same of the others, thus, backpressure caused by the highest one may interrupt the discharge of the rest with lower set pressure.

 

[BigInch]

http://www.chemengsoftware.com/techinfo/headers.htm

http://virtualpipeline.spaces.msn.com

 

[4Pipes]

I fully agree with Shmulik. I assume that you are talking about manifolding the valve outlets. Its unusual to manifold steam relief valves together because of the flow interaction already mentioned. You will also hit problems with the thermal expansion and dead load of the header putting a load back on the valves which are difficult problems to solve practically. If the complexity scale for the manifold option is 1000, then independent upcoupled tail pipes in accordance with ASME B31.1 App II will have a complexity of 1. If I understand your units you will be looking at something like a 3"x4" relief valve. 4 off 8" say uncoupled tail pipes pointing straight up will be simpler than a 10-12-14" or larger manifold with a driving back pressure of less than a couple of psi.
There is also the question of maintence. The manifold option would require all boilers to be closed down to service one relief valve. (Same goes for the good idea of saving money by not having individual boiler isolation valves which came to grief on a refinery I know). I would guess the maintenance argument would kill off the manifold option.

 

[BenThayer]

i am not afraid to calculate the header sizing but i would stay away from it from a maintenance viewpoint. pain in the neck to service the boilers and relief valves with the others on line. even with valving and locked open/closed valves, etc. i would avoid if possible.