Pressure relief valve selection

[CONROD]

Hello all
I have been asked to replace some Henry PRV's fitted to a YORK chiller - YCAJ665T9GSI50PA circa 1994, still operating on R22. The manufactueres data plate stated that the desgn working pressure is 27.6bar high side & 21bar low side. The PRV's are installed on a 1/2 line off the main suction return line from the shell 7 tube evaporator to the compressor. The PRV's are therefore installed on the low side, but are rated at 27.6bar. There are no PRV's installed on the high side that I can see or any other type of relief device. Are the PRV's installed of the wrong rating or installed in the wrong location, they appear to be original factory items though. My thoughts are that they are in the correct location in that they are protecting the only "vessel" on the chiller as there is no liquid receiver as such, but that they should be rated at 20.7 bar, not 27.6bar. I have not been able to get any information from YORK as yet.
Your thoughts would be appreciated!!
CONROD

[Magoo]

generally speaking unfired pressure vessel relief safety valves are rated at the limit of the pressure vessel design, clearly stamped on vessel somewhere, can be in a pipe line so long as there are no isolation valves between vessel and relief valves.

[coolman]

Pressure relief valves are set to maximum design pressure of installtion, ussually here 1.4 times maximum operating pressure (dutch law)