Investigation of force assisted suction reed valves in hermetic reciprocating compressors

Reed valves are widely used in hermetic reciprocating compressors and are responsible for a major share of thermodynamic losses. The suction valve in particular, which is opened for almost the entire suction phase, has a very significant improvement potential. Suction valves in hermetic reciprocating compressors are usually opened only by the pressure difference created by the moving piston and should be closed before the compression phase starts, in order to avoid a reversed mass-flow through the valve. The valves are thus preloaded, which, on the other hand, results in a higher flow resistance. In this work, a force-assisted suction valve is investigated. An electromagnetically actuated spring generates an additional force acting on the conventional suction reed valve. This force leads to a completely different valve movement and a significant reduction of the losses caused by the suction valve. A conventional suction valve flutters during the suction phase. Thus, it hits the valve seat several times which has, beside an increased flow resistance, negative influences on the reliability of the reed valve and noise emissions. With the help of the additional force, it is able to overcome the opening delay due to the preload and the oil ‘stiction’ effect. Furthermore, the suction valve can be held open during the whole suction phase, and it closes smoothly in time near the bottom dead centre of the piston. The investigation of the force-assisted suction valve is done by numerical simulations as well as by experiments. Results show an improvement of the coefficient of performance by approximately 0.7%–1.6% depending on the operating conditions.