HYDRAULIC SELF-HOLDING TYPE TWO-POSITION CHANGEOVER VALVE

摘要

The invention relates to a two-position switching valve having hydraulic self-holding properties and comprising a closure piston disposed in a flow path for displacement between an open position and a closure position for controlling a pressure between a maximum value and a minimum value, and operatively coupled to a control piston mounted for displacement in a housing. In known switching valves of this type, a creeping approach of respective switching points is scarcely avoidable under certain operating conditions. In accordance with the invention, a reliable switching function is achieved by forming the housing bore as a continuous stepped bore for slidably guiding therein a stepped piston consisting of a closure piston, a control piston, and a piston portion and by providing alternately openable and closable flow connections therein permitting an annular space between the closure piston and the piston portion to communicate with an annular chamber adjacent the control piston in the closure position of the closure piston, and the annular chamber to be pressure-relieved in the open position of the closure piston. These provisions result in the generation of a servo force for abrupt switch-over operation of the valve.