| 摘要 |
A piston pump, particularly a radial piston pump, has a plurality of cylinder-piston units (1, 2, 3, 4, 5) of which the pistons (6) are driven by a tappet sheave (7) and which transport a pressure medium by means of different inlet return valves (9) from a suction pipe (10) via different discharge return valves (11) to a pressure medium circuit. A plurality of pistons (6) may be pushed without any mechanical thrust mechanism by a simple control pressure against the tappet sheave (7). In order to obtain a transportation by the cylinder-piston units only when a consumer needs it, the closure springs (20) of the inlet return valves (9) are prestressed to a predetermined value. If the control pressure exceeds said predetermined value, the inlet return valves (9) are open, the pistons (6) are pushed against the tappet sheave (7) and the cylinder-piston units effect a transport. As various consumers do not temporarily need pressure medium, the cylinder-piston units have to effect a transportation only where there is effectively a need for pressure medium. To this effect a pilot valve (21) is arranged in the suction pipe (10); it closes at least partially the suction pipe (10) if the pressure prevailing in the suction pipe (10) exceeds the control pressure by a predetermined value. The pilot valve (21) is controlled by a pressure limiter (34). Those two valves enable to connect or disconnect separately or by groups the suction pipes (10) leading to the various inlet return valves (9). The control pressure is operatively generated by an additional cylinder-piston unit (14) of which the piston (15) is maintained against the tappet sheave (7) by means of a mechanical thrust mechanism (16).
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