Refrigeration circuit

A refrigeration circuit comprising:

• a low stage compressor, a high stage compressor, a condenser, an expansion device, and an evaporator;
• refrigerant flow means connecting the high and low stage compressors, the condenser, the expansion device, and the evaporator to form a closed, vapor compression refrigeration loop, and including
• a low pressure line for conducting refrigerant vapor to the low stage compressor,
• an interstage line for conducting refrigerant vapor discharged from the low stage compressor to the high stage compressor,
• by-pass means connecting the low pressure line with the high stage compressor for conducting refrigerant vapor therebetween to by-pass the low stage compressor, and
• a quench line connected to the by-pass means for conducting liquid refrigerant thereto;
• and
• a check-quench valve located at the intersection of the by-pass means and the quench line and having
• a quench position blocking the by-pass means and opening the quench line to direct refrigerant from the low pressure line serially through the low stage compressor, through the interstage line, and into the high stage compressor, and to inject refrigerant from the quench line into the refrigerant vapor discharged from the low stage compressor, and
• a by-pass position opening the by-pass means and closing the quench line to direct refrigerant from the low pressure line through the by-pass means and into the high stage compressor to by-pass the low stage compressor.