Abstract: A pool sweep having a continuously-cycling, flow-interrupting valve at the upstream entrance to an inertial flow chamber. The valve has an entrance mouth with one or more closure lips pivoting been open and closed positions to open and close the mouth. The lips are biased towards closure with low creep biasing means, as by materials having a strain at its elastic limit of below 0.5 such as one or more metal springs urging the lip toward closure. The magnitude of the opening bias throughout the range of movement of the lips between open and close under dynamic flow conditions is substantially less than the closing force created by the water flow through the valve mouth urging the lips towards closure and substantially greater than the closing force imparted by flow through the mouth during lip travel from full closure to the open position.

Abstract: A vacuum pool cleaning device of the interrupted flow type having a valve in the form of a pair of lips biased to an open position by the inherent elasticity of the plastic material forming a portion or all of the valve in which an auxiliary biasing structure with low creep properties is applied to the lips of the valve and function to compensate for the memory loss during a cycle of operation of the valve in the plastic, due to its relatively high creep properties, by returning the lips substantially to their open position when the operation of the unit is stopped, so that during the at-rest period prior to the next cycle the plastic material can reestablish its memory.