Jan 19, 2025 · API 526 refers to ASME B16.34 for the flange ratings. I would like to understand the mechanical background behind the above, why larger PSVs tend to have lower limits for inlet flange rating.

Jun 14, 2006 · The PSV comes standard with an as-cast Class 300 flange on its inlet. The manufacturer machines the inlet flange just enough to conform to the fit up requirements of the Class 150 flange(bolting and raised face).

Aug 24, 2010 · If your inlet pipe is one or more sizes larger than the nominal inlet size of the PSV, then it's OK to use a standard (reduced port) gate valve under the PSV. Other types of valves are OK too but check to be sure the x-sec area is at least as large as …

Aug 27, 2007 · The pressure at the PSV outlet flange/tailpipe inlet flange is 10 psig + frictional pressure drop working backwards from the header. This assumes there is negligible frictional pressure drop in the header such that there is no built-up backpressure due to the header.

Jun 27, 2007 · The built-up backpressure calculation assumes the flow upstream of the expander (i.e. in the outlet flange of the PSV) is "well-developed flow" that can be represented by continuous mathmatical relationships to the flow in the expander and further downstream.

Aug 4, 2005 · When we run several of our PSVs in Flarenet we get mach one at the PSV outlet flanges. Does this mean these flanges are undersized? In some cases we need to go up two sizes to avoid sonic.

Oct 14, 2003 · PSV can be on vessel or outlet piping provided that (a) there is no restriction to flow which would reduce the PSV relief rate and (b) the total pressure drop between the vessel nozzle and the PSV inlet flange is <3% of the valve set pressure.

Jul 31, 2015 · Yes- the discharge can and usually does have a lower flange rating than the inlet. Conventional relief valves cannot have a back-pressure greater than 10% of their set pressure, or else a different design of device must be specified to be safe.

Feb 22, 2018 · It is possible for a flange to be bored to a different diameter than Sch STD. Are we supposed to assume that all PSV manufacturers use Sch STD bores unless their catalogues indicate otherwise?

May 5, 2019 · The pressure at the PSV outlet flange is the backpressure of the flow in the outlet line plus/minus any hydrostatic pressure due to elevation. 2. Excessive vibration is not good.