Hydraulic pump with high pressure piston - extending through annular low pressure piston with spring-loaded non-return and throttle valves

The pump is particularly intended for hydraulic lifting gear and comprises a high pressure piston extending into a larger diameter cylinder with low pressure piston whose end faces are connected by bores containing non-return and throttle valves respectively. The low pressure piston is ring-shaped and carried on a cylindrical extension of the high pressure piston such that its end faces remain at a distance from the cylinder ends at top and bottom dead centre positions. The low pressure piston has six axial bores with spherical valve closure members, three of which act as non-return valves and three as throttle valves. Each set of three valves is spring-loaded via a pressure plate and spring arranged at either side of the annular low pressure piston.