An Experimental Procedure for Determining the Equivalent Clearance for Cylinder Piston Seals of a Low-Speed Long Stroke Stage in Dynamic Formulation

This paper discusses the basic definitions of the terms “conditional clearance” and “equivalent clearance” in piston–cylinder sealing, providing a distinctive description of each and highlighting their importance in calculating mass flows. The issue of the lack of recommendations regarding the parameters of the equivalent clearance for slow-speed compressor stages is identified. An experimental methodology and a test rig have been developed to determine the parameters of the equivalent clearance. The conducted research has shown that the size of the equivalent clearance is highly dependent on the cycle time, varying from 0.5 to 1.5 µm depending on the working gas parameters and the number of seals installed on the piston. It has been determined that in the pressure range from 0.1 to 12 MPa, with cycle times between 2 to 4 s, it is not advisable to install more than seven sealing rings, as the size of the equivalent clearance changes insignificantly.