Modeling the stiction effect in automatic compressor valves

Abstract

The stiction effect is a source of thermodynamic losses in compressor suction and discharge systems. Deformation of the lubricant film between the valve and the seat delays the valve opening, as larger pressure differences between the cylinder and the discharge or suction chambers are needed to overcome the stiction force. A model is presented for the dynamic behavior of a ring-shaped lubricant oil film between a discharge valve and the seat. The valve is allowed to move under the action of an external force due to the time-dependent pressure difference between the cylinder and the discharge chamber. The main contributions of the model are the consideration of a finite oil amount between the valve and the seat and relationships for calculating the film thickness initial condition. At typical conditions of discharge systems of domestic refrigeration compressors, viscous effects are the dominant component in the oil stiction force under dynamic conditions.