Experimental study of friction in hydraulic actuators with sealless pistons

Use of seals on the piston surface of servo hydraulic actuators causes, apart from excessive wear, positional inaccuracies arising out of large mechanical friction due to physical contact. In order to improve their performance, modern servo hydraulic actuators use pistons with tapered surfaces. When such pistons move within the cylinder there is a chance of generating sufficient oil pressure to lift the piston owing to hydrodynamic action. Theoretical study on three types of such pistons was reported earlier. In this paper, experimental work carried out on those tapered pistons is presented. A new test-rig has been developed to test the actuators, and the test results confirm the main findings of the theoretical study. © 1994.