Scope of safety relief valves between reciprocating compressor lines

Not knowing the system I can only give you some things to look for. First if there is a relief valve betweent the suction and discharge, is it vented back to the suction end? If so, it would be a pressure regulator, used in the event of a blockage of the discharge line.

Safety relief valves are used when the system is over pressure and they are normaly vented to the outside. They are normally found after the discharge line.

Hope that helps

First Thanks for reply

The safety valves in discusion are placed form discharge line direct to suction line and are located close to the compressor, before to isolation valves. My idea was initially, this valve was instalalled to not exceed the pressure ratio of the compressor. But now I am asking, the valves was installed to avoid an increasing pressure drop in the rest of the system where the compressor operating.

Kind regards

Aurel

Piping and vessel Design Codes require a relief valve in the discharge line of any positive displacement compressor or pump , before any discharge block valve, to protect the piping and device from a 'blocked discharge' overpressure condition. These relief valves are normally sized large enough to pass the required volume at maximum discharge pressure rating and the maximum inlet pressure possible, thus ensuing against overpressure. These ARE NOT 'pressure control' devices, but emergency pressure relief safety devices and are not designed for continuous flow. There is normally no flow through them.

There may also be a 'spill-back' system with a true control valve to regulate the pressure in each stage suction (or discharge) drum. The compression ratio in each stage of hydrogen compressors must be controlled to less than 3:1 to avoid overheating the discharge valves. Often 'clearance pockets' in the cylinder head are used for this rather than energy wasting 'spill-backs'.

If memory serves me correctly, with inter-cooling to 130F between stages, it takes 4 stages of compression to get from 100 psig to 3400 psig without overheating the discharge valves in the cylinder heads. Short valve life will result from overheating.

I'd guess they are there for either rod load protection or cylinder MAWP protection.