Combined hydraulic valve with switching and pressure reduction functions e.g. for holding brake

摘要

The present invention pertains to a dual-function hydraulic valve (1), i.e. a control valve and a pressure reduction or limitation valve at the same time. The inventive combined hydraulic valve (1) encompasses a valve casing (2) with a first central pressure connection (P), a second central pressure connection (Br) and a movable flow check piston (7) in the valve casing (2). The flow check piston (7) presents a pressure surface (16) enabling it (P), when the first central connection is put under supply pressure (Pp), to move from its basic position against an opposing force proportional to said supply pressure (pp). It also presents a first control ridge (40) and a second control ridge (41). The first control ridge (40) is used to link the first central pressure connection (P) to the second central pressure connection (Br), starting from a first set minimum displacement of the flow check piston (7) which corresponds to a lower threshold value (p1) of the supply pressure (pp). The second control ridge (41) is used to break the linkage of the first (P) central pressure connection with both the second central pressure connection (Br) and the pressure surface (16), starting from a set maximum displacement (7) which corresponds to a higher threshold value (p2) of the supply pressure (pp).