Investigation on thermodynamic state and valve dynamics of reciprocating compressors with capacity regulation system and parameter optimization

Compressor thermodynamics under varying capacity loads are difficult to predict due to the interaction between the valve-sealing element motion, unloader behavior, and fluid flow. In this paper, a new comprehensive mathematical model of piston compressor under various gas flow loads is established, which is combined with a reciprocating compressor, intake valves, hydraulic plunger cylinder, and unloader, and the model is validated by experimental data. Results show that the installation of finger-type unloaders clearly leads to an increase in flow loss. With a reduction in the flow load of compressed gas, the closing impact velocity of the suction valve plate increases, and the valve appears to oscillate under capacity regulation conditions, leading to premature fatigue damage of the valve component. The optimal combination of design parameters for a suction valve in the capacity regulation system is a 2.7 mm valve lift with a 2100 N/m spring stiffness, yielding a minimum valve resistance loss within admissible valve dynamic motion. The reset spring stiffness of 20 kN/m is chosen as the optimal parameter value by which the impact speed of the suction valve plate at the valve seat is clearly reduced, avoiding excessive impact stress in the reset process.