The energetic efficiency of the small hermetic compressors of refrigeration is mostly attributed to the good performance of its valves in the control of the gas flow.
Compressors for domestic refrigeration appliances employ one-way valves that control the gas flow during operation. A suction valve controls the gas flow, which comes from the suction line connected to the low pressure side of the refrigeration system, and which is drawn through the compression cylinder, while a discharge valve controls the flow of the already compressed gas to be directed to the high pressure side of the refrigeration system.
The suction and discharge valves are usually formed by one or more gas passage orifices located in the valve plate, and by flexible vanes usually obtained from a thin steel plate and which are fixed by one of the ends thereof, so that when a pressure differential occurs through the valve the flexible vane is displaced, allowing the gas to pass in the preferred required direction.
Some design aspects should be considered in order to obtain an adequate operation with this type of valve, such as: area of the gas passage orifice; rigidity and natural frequency of the flexible vane and mounting characteristics with eventual acoustic filters.
Besides the operational characteristics, the reliability aspects should also be considered, which means to achieve an infinite life condition in relation to fatigue failure within the usual working ranges of the compressor. The main types of fatigue failure that occur in the flexible vane are: high bending stress in the region close to the valve fixation; high bending stress in the region over the gas passage orifice; high impact stress against the seat or against the stop.
The manufacture of the current valves takes into account the design restrictions, which fact, in a certain way, defines the working efficiency thereof. Such efficiency is strongly influenced by the degree of rigidity defined for the flexible vane.
There is a correlation between the rigidity of the flexible vane and the power that is consumed to carry out the suction or discharge processes, in which the higher the power the higher is the rigidity. Dynamic operational aspects of this component should be considered so that a reduction in the rigidity effectively results in an improvement in the performance of the compressor, in which the correct closing point of the valve must be achieved to avoid backflows.
Thus, a reduction in the rigidity of the flexible vane can improve the performance of the product, but results in higher flexibility of this movable component and, in determined working conditions, the amplitude of its displacement will eventually reach amplitudes to which the bending stress in the fixation region reaches prohibitive levels.