Dual function hydraulic valve and circuit

In a pump for providing a pressurized liquid to a hydraulic circuit, an adjustable relief valve, wherein the hydraulic circuit includes a pressure conduit for receiving pressurized liquid from the pump and a relief conduit for receiving pressurized liquid from the pump when the relief valve is open, the adjustable relief valve comprising

• a valve conduit for connecting the relief conduit to the pressure conduit to provide fluid communication therebetween;
• a conduit blocking element for, when the adjustable relief valve is in a closed position, blocking the valve conduit to impede fluid communication between the pressure conduit and the relief conduit, and for, when the adjustable relief valve is in an open position, permitting fluid communication between the pressure conduit and the relief conduit;
• a biasing means for biasing the conduit blocking element to the closed position when the downstream pressure level is less than the actuation pressure, wherein the biasing means is remotely adjustable to change the actuation pressure;
• and,
• remote control means for remotely adjusting the biasing means.

A method of modifying a hydraulic circuit to operate at multiple pressures, the hydraulic circuit having

• a reservoir containing fluid at an upstream pressure level;
• a pump for receiving a fluid from the reservoir and for raising a fluid pressure of the fluid from the upstream pressure level to a downstream pressure level;
• and
• a pressure conduit for receiving the fluid from the pump;
• the method comprising the steps of incorporating into the hydraulic circuit
• (a) an adjustable relief valve for receiving fluid at the downstream pressure level from the pump, wherein the adjustable relief valve is
• (i) connected to a relief conduit and to the pressure conduit,
• (ii) operable to open to connect the pressure conduit with the relief conduit when the downstream pressure level exceeds an actuation pressure level,
• (iii) operable to close to isolate the pressure conduit from the relief conduit when the actuation pressure level exceeds or is equal to the downstream pressure level, and
• (iv) remotely adjustable to change the actuation pressure;
• and,
• (b) remote control means for remotely adjusting the adjustable relief valve.