Pressure control arrangement for hydraulic brake systems

A pressure control arrangement for hydraulic brake systems comprising a plunger piston in a sealed slidable relationship in a bore which defines a first chamber connecting with at least one wheel brake cylinder, said first chamber being connected with a brake pressure source through a first valve which is kept in the open position by a mechanical means when said plunger piston is in its end position wherein the volume of said first chamber is its smallest, said plunger piston being displaceable into said end position by pressure supplied by an auxiliary pressure source, said auxiliary pressure being controllable for affecting anti-skid control for which purpose the auxiliary pressure source is connected with a control chamber lying opposite said first chamber through at least one auxiliary valve, a control piston positioned in an axial bore in said plunger piston joined to a closure member of said first valve having a first end acted on by the pressure from said brake pressure source in the opening direction and a second end acted on by the auxiliary pressure in the closing direction, said acted on ends being dimensioned so that said closure member is always preloaded in the closing direction when auxiliary pressure is available.