Analysis, design and comparison of different types of pistons for sealless pneumatic cylinders and valves

The paper presents a theoretical and experimental analysis of sealless pistons featuring a special geometry capable of eliminating friction in pneumatic cylinders and valves. Three different piston geometries were investigated: tapered, stepped and slot-pocket. Performance was evaluated for each geometry in terms of pressure distribution, leakage flow rate, and the self-centering force on the piston. The piston configuration which provides the best tradeoff between self-centering thrust and leakage flow rate in the air gap was also determined. The theoretical and experimental results obtained with the different piston designs were then compared.