An unloader valve is a type of pressure control valve that is used to dump excess fluid at low pressures. There are several types of unloader valves, such as direct-acting or pilot-operated. Direct-acting valves consist of a spool held by a spring. When pressurized fluid flows into the valve, putting pressure on the spring. When the spring setting is reached, the spool opens and fluid is bypassed to the tank. Pilot-operated valves work much the same, although there is an additional spool called the unloading spool. This spool opens when pressure in the circuit goes above settings. This allows fluid to enter the tank with minimal pressure loss.