Hydraulic steering system automatic changeover valve - has spring chamber extending axial plunger bore, and has constant cross=section throttle

摘要

The automatic change-over valve has branches for main and standby pumps, the consumer appliance and a hydraulic accumulator. Pressure from the main pump thrusts a valve plunger against spring force into a position, freeing the passage to the consumer appliance, while between the branches for the main pump and the accumulator is a constant throttle. Control edges on the plunger and housing form a further variable throttle between the accumulator and main pump branches. A spring chamber (16) forms an extension of an axial bore (33) and constant cross section throttle (34), while a variable throttle (D2) lies between this chamber and the accumulator branch (5). The cross section of the constant throttle is such that the pressure drop across it, when the main pump delivers, is approximately 2 bar, corresponding to the mean spring pressure, divided by the cross-sectional area of the plunger (27).PS.