Unloading valves are used in hydraulic circuits, these valves would stop or remove the flow of the pump back to the tank when the machine is not operating. ... These valves are pressure controlled device which would transfer the excess fluid to the tank. Unloading valves are mostly used in high-low pump circuits.

What is purpose of using unloading valve?

Unloading valves are typically used in high-low circuits. The circuit is sometimes referred to as a fast approach, slow feed circuit. The unloading valve is put to good use in a system where a high flow volume is needed at a lower pressure, and then later a low flow volume is required with a higher pressure.

How does an unloading valve work?

When the air pressure inside the compressor's tank reaches the pressure switch's cut out pressure (the point when air is no longer delivered), the switch automatically trips off and interrupts the power supply to the motor. This process causes the unloader valve to open and vent the accumulated air.