In the field of “Oil & Gas”, reciprocating compressors are widely used.
US2002/0141884-A1 describes an unloader system is provided for a reciprocating gas compressor. The system includes an unloader valve assembly including a valve member controlling flow between compressor cylinder and a clearance bottle. Opening and closing of the valve member is controlled by manipulating a control pressure acting through a manifold against the stem of the valve member by means of a pressure regulator connected in series with a pressure source. When the pressure in the compressor cylinder acting on the heads of the poppet valve members exceeds the control pressure acting on the stems, the poppet valve members open, partially unloading the compressor.
Each cylinder head of the reciprocating compressor described in the cited document has an annular chamfer with a concave surface partially facing the valve openings.
In different known designs, the cylinder head may a have plurality of slots, each facing a valve opening. Each slot have a concave surface, shaped as a part of a sphere (therefore with a constant radius).
The fluid, when aspired into the compression chamber and when leaving it, runs onto the concave surface of the chamfer or of the slots. This generates pressure losses that lower the efficiency of the compressor.