Hydrostatic radial piston pump

A hydrostatic radial piston pump, comprising a housing defining a suction chamber;

• an eccentric;
• a pressure valve member spaced from said eccentric and having a convex support;
• a movable structural unit arranged between said eccentric and said pressure valve member, said unit including a cylinder having a supporting face with a sealing edge spring-biased against said support of said pressure valve member, and a piston with a piston shoe spring-biased against said eccentric, said supporting face having an inner annular face portion, an additional outer annular face portion increasing said supporting face, and a circumferential groove formed between said face portions, said outer annular face portion of said supporting face also having at least one substantially radial groove communicating said circumferential groove with said suction chamber and performing only supporting function without performing sealing function as well as being lubricated through said grooves;
• and a pressure spring arranged to bias said supporting face with a sealing edge of said cylinder against said support of said pressure valve member and to bias said piston shoe of said piston against said eccentric in force-transmitting manner, said spring having a predetermined force acting between said annular face portions or said supporting face upon said support of said pressure valve member, said annular face portions of said supporting face having a predetermined dimension increased by the provision of said additional outer annular face portion and selected so that a ratio of said force and said dimension does not exceed substantially 2.5 kg/cm.sup.2.