Apparatus for the control of a hydromotor

In an apparatus for controlling the application of fluid under pressure to a hydraulic load device, the apparatus including a source of fluid under pressure, a throttling direction control valve for selectively permitting the pressure fluid to flow to the load device, first conduit means for interconnecting the load device at a first port thereof and the direction control valve, and second and third conduit means for interconnecting the direction control valve and the load device at a second port thereof;

• compensating valve means, connected between said second and third conduit means such that said second conduit means connects said compensating valve means and the direction control valve and said third conduit means connects the load device and the compensating valve means, for preventing sudden driving of the load device for maintaining constant load device speed in the case of load changes thereon indepedently of direction, and for closing without leaking pressure fluid, said compensating valve means having a control input and a control piston with means for connecting said control piston with said control input;
• the improvement comprising
• a pressure reducing valve having input and output flow connections, a control connection, means for connecting said input flow connection with the first conduit means and means for connecting said output flow connection with said control input of said compensating valve means, said control connection being on the side of said pressure reducing valve and having means for connecting said control connection to said control input of said compensating valve means, whereby the pressure of fluid supplied to said control input of the compensating valve means, the pressure gradient across the direction control valve and the flow through the direction control valve are maintained substantially constant when the source of fluid under pressure is connected to the first conduit means;
• fourth conduit means connecting the side of the control piston opposite the control input with the second conduit means;
• and
• spring means for biasing the control piston toward the control input.