Hydraulic systems

Abstract

A hydraulic system including a compensator connected between the service ports of the control valve and the load and arranged to restrict the flow in one or both of the service lines so as to maintain a constant pressure difference between the supply pressure and the pressure at the valve service port supplying fluid to the load. The compensator may be connected in both service lines and arranged to restrict the flow equally in each of them. Alternatively a single-sided compensator may be used, and if the load is liable to over-run it must be connected in the service line which is downstream of the load when over-running.

I claim: .[.1. A hydraulic system including a source of hydraulic pressure, a load, a four-way control valve arranged to control the supply of hydraulic pressure to said load, said valve having a pair of service ports, a pair of service lines connecting said service ports to said load, a compensator being connected in at least one of said service lines and being arranged to restrict the flow of hydraulic fluid in said service line so as to maintain a constant pressure difference between said source pressure and said pressure at that one of the valve service ports that 
     
        supplies fluid to said load..]. 2. A hydraulic system .[.according to claim 1 in which the compensator is connected in both service lines and is arranged to restrict flow equally in each of them.]. .Iadd.including a source of hydraulic pressure, a load, a four-way control valve arranged to control the supply of hydraulic pressure to said load, said valve having a pair of service ports, a pair of service lines connecting said service ports to said load, a compensator being connected in at least one of said service lines and being arranged to restrict the flow of hydraulic fluid in said service line so as to maintain a constant pressure difference between said source pressure and said pressure at that one of the valve service ports that supplies fluid to said load, said compensator being connected in both service lines and is arranged to   
     
     
        restrict flow equally in each of them. .Iaddend. 3. A system according to claim 2 in which the control valve is a pilot-operated servo valve, and the pilot pressure is arranged to operate a shuttle valve so as to select the service line supplying fluid to the load, and to apply the pressure in 
     
     
        that line to the compensator. 4. A system according to claim .[.1.]. .Iadd.2 .Iaddend.including a shuttle valve, a flow-sensing valve is included in one of the service lines to provide pilot pressures for operating said shuttle valve which selects the service line supplying fluid to the load, and to supply the pressure in this line to said 
     
     
        compensator. 5. A compensator and pilot operated shuttle valve incorporated in a block provided with ports on opposed flat surfaces, constructed and arranged so that it can be assembled with a control valve to form a system according to claim .[.1.]. .Iadd.2.Iaddend..