To relieve refrigerant from high pressure side to low pressure side only back pressure independent relief valves should be used (BSV/ POV).BSV ➁ can act either as a direct relief valve with low capacity or as a pilot valve for POV ➀ main valve. When the discharge pressure exceeds the set pressure, BSV will open the POV to relieve high pressure vapour into the low pressure side. The back pressure independent relief valves are installed without change over valve. In case it is necessary to replace or readjust the valves, the compressor has to be stopped. If a stop valve is mounted in the discharge line from the oil separator, it is necessary to protect the oil separator and the compressor against excessive pressure caused by external heat or compression heat. This protection can be achieved with standard safety relief valves SFA ➄ combined with a change over valve DSV ➂.
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