Pressure pumps are complex, precise pieces of equipment, and they require routine maintenance and replacement of parts as they wear over time. One such part is the unloader valve; this component is vital for the proper operation of pumps that supply pressurized water on a demand basis. If you have a pump system that is malfunctioning, one place you should check for trouble is the unloader valve. Here is more information about how to diagnose problems with unloader valves and how to replace them should they fail:
What does an unloader valve do?
The unloader valve serves as a gatekeeper for the flow of pressurized water within a pump before it passes out of the exit hose and pressure nozzle. Unloader valves automatically regulate when water flows into the nozzle or recirculates back into a pump during periods of non-use. During non-use, the water inside the pump becomes a closed loop with no "new" water allowed to enter. Once the operator begins releasing pressurized water again, the unloader valve then stops closed circulation and allows fresh water to enter the system.
Pressure pumps use positive displacement technology, which simply means that water continuously moves through pumps, as opposed to impulse pumps which only operate in an on or off fashion. With positive displacement pumps, an unloader valve is necessary because it prevents the pump from building destructive internal pressures.
What happens when unloader valves fail?
A failing unloader valve is immediately noticeable because of its critical impact on the performance of pressure pumps. Unloader valves that aren't working properly can cause these problems:
Pump motor stalling – if a pump is powered by a gasoline or diesel engine, stalling whenever the operator ceases to use it is a good sign of unloader valve failure. The buildup of pressure locks the pump's internal components, which in turn prevents the rotation of the powered engine shaft. Such a problem indicates the unloader valve is not properly recirculating water back into the pump.
No pressurized water available – an unloader valve that is stuck in the bypass position will prevent water from entering the pressure hose and nozzle. If your pump's engine is functioning properly, an adequate supply of water is entering the system, and there are no leaks in your system, then an unloader valve failure is a strong possibility when you have no access to pressurized water.
How do you replace an unloader valve?
Fortunately, unloader valves are usually located in a prominent, accessible location on pressurized water systems. Typically, they can be found near or integrated with high pressure water outlets. In addition, the unloader valve will often be connected to a hose that carries water flow back into the pump for recirculation. Finally, unloader valves will have a protrusion which covers a spring used for maintaining the flow of water; this protrusion may appear as a knob, or you be able to see the spring beneath it.
While the specific replacement procedure for defective unloader valves is unique to unit make and model, there are a few guidelines below that will help you with most unloader valve installations:
Make sure all the inlets and outlets on your new valve match the old part before installation.
Remove any fittings from the old valve if they aren't included with the new valve, and install them on the new valve.
Use a few wrappings of pipe thread tape to create a waterproof seal between the pump and unloader valve.
Cut two centimeters from the ends of hoses that fit directly to the unloader valve so you will have fresh, unstretched hose material to attach to the valve. Use new hose clamps if the old ones are rusted or appear worn.
Adjust the tension on the unloader valve spring so that it operates at the pressure specified by the pump manufacturer; too high or too low pressure can cause damage or prevent the unit from operating reliably.
5 January 2015
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