An unloader valve works by diverting water flow into a bypass as soon as a trigger gun valve is closed. These two valves work together to create a unique system that directs water into a float tank or a pump inlet. Unloader valves are used to circulate water into the inlet side of a pump, while trigger gun valves control the flow of water.
There are two types of unloader valves: the pressure-actuated unloader and the flow-actuated unloader. The pressure-actuated unloader works by responding to increases and decreases in water pressure. The flow-actuated unloader relies completely on water flow; a halt in water flow increases the internal pressure.
Most unloaders are designed to function with 5 to 10 percent of water flow in the bypass at all times. This is true for all pressure-actuated unloaders. These types of unloaders usually need at least 10 percent of water capacity in the bypass. The water in the bypass provides a type of cushion between the valve ball and the seat to help lessen the impact of two metals being forced together during normal valve operations.
No machine that uses unloaders should run in a bypass mode continuously. This is because the closed loop rapidly increases the temperature of the water. Most water pumps are not designed to handle water that gets hotter than 140 degrees Fahrenheit.