The pressure washers unloader valve is commonly understood as a gate-keeper or a safety device that controls the direction of water flow exiting the pump.
Despite of spray gun being open or closed, a positive displacement pump work is to deliver water and if the spray gun is closed then it is the function of the unloader valve to redirect the flow of water back to the pump’s inlet side.
This way the build-up of a dangerous high-pressure is prevented and the component parts are guarded against any failure.
Pressure washers or cleaners are installed with two types of unloaders:
Trapped Pressure Unloader
Flow Actuated Unloader
Derived from a Latin word valva, valve means a leaf in a folding door.
Unloader valves also function as ‘traffic-cops’ as they direct all the water-flow in a pressure cleaning system.
When there is no water flow from the spray gun nozzle then the unloader valve works to redirect it for a secure pressure outlet.
Bypass mode: While the cleaner is in a ‘bypass mode’, the unreleased water is diverted back to the pressure washer pump’s inlet side. Water circulates through the pressure-pump and goes back to the unloader valve’s inlet side.
Again the water is released by the spray gun or redirected to the pump. This procedure of continued re-cycling of water through the pump is known as ‘cycling’.
These are most commonly used unloader valves and are known to sense then get activated by building pressure at the pump output.
These are said to initiate bypass mode in the straight response to building pressure – between the pump output and the spray gun hose.
These are also referred to as “pressure valves” as when the cycling is intervened and the water is re-released to the spray gun by trapped pressure valves resulting into a spike of water.
Note that the operators should remain prepared for any sort of ‘kick back’ effect that could happen on the spray gun or wand for avoiding any loss of control or injury.
These unloader valve types answer to any interruption of water flow to the nozzle. Any decrease in the water flow is sensed by these valves and then the bypass loop in response is initiated.
Since no pressure is trapped, so in turn no ‘kick back’ occurs on the water re-release. The pressure cannot be regulated by the operators by downsizing the opening size of the nozzles, when they use the flow actuated unloader valves.
The loss of flow is detected by the flow actuated unloader valves and repeated cycling is their reaction to it.
As mentioned above also the dangerous build-up of pressure is prevented by cycling though some additional safety concerns may arise during the bypass mode.
Since there are no chances of cool water to enter the pump during bypass hence the cycling water could be heated-up to dangerous temperatures.
A temperature of 140º F is what most of the pressure washer pimps can withstand. Higher temperatures above this could damage the pump. Damage could also be caused to plungers, seals, pump packing, or the short bypass hose.
There are thermal relief valves that could offer some protection against excessive heat build-up. It is ensured by them that the cool water is released when the temperatures exceed 145º F.
Overheating In Bypass:
The bypass mode should not be the case continuously as the water temperature tends to rise rapidly due to the pump friction thereby increasing the water temperature. As we have mentioned about the ideal temperature levels above – 140º F, similarly 2 -3 minutes is the ideal time for bypass mode.
The water is replaced in the loop when there is occasional discharge at the gun, and in turn pump damage is restrained from high temperatures.
When you squeeze the spray gun trigger, cycling is always interrupted and cool water is introduced to the system.
Regulate Pressure Using An Unloader Valve:
Be it the flow-actuated or the trapped pressure unloader valve, both these types can be used to control the machine pressure by tension adjustment on the spring which is designed to hold the piston in the unloader valve.
The spring tightening on a flow-actuated unloader reduces the pressure while on a trapped-pressure unloader, spring tightening leads to pressure increase.
When the adjustment bolt is loosened on a flow-actuated unloader then the piston that controls the valve rises. This allows more water to go through the gun and a higher operating pressure is built-up.
When the adjustment bolt is loosened on a trapped pressure unloader, the spring tension is reduced and results in lessening the piston assembly tension. This means that even at low temperatures it can open into bypass, allowing lesser pressure to force out and result a lower operating pressure.
Adjusting A Trapped Pressure Unloader Valve:
The adjustments of the trapped pressure unloader valve should be done when the pressure washer is operating while keeping the trigger pressed when the water is flows through the gun.
Loose or screw away the initial adjusting position keeping away from the body, reducing the tension on the spring.
For ensuring that the unloader valve is working, release the trigger. Then the trigger should be pressed that allows the system to develop its operating pressure using that adjustment.
Pressure gauge reading should be taken care of here.
The adjusting bolt should be tightened and the trigger should be pressed simultaneously.
Until you get the desired pressure repeat this and make use of gauge for monitoring the systems.
For checking the spike pressure release the trigger. This all needs to be done when there is pressure in the system and the water is flowing.
For flow actuated unloader valves the adjustment procedure is completely opposite.
Q1. What is the role of an unloader valve in a pressure washer?
Ans. The unloader valve works to divert the flow of the water. The diversion is done form the pump’s outlet side back towards the inlet thereby resulting in a loop back water flow to the pump. Under operating pressure there is practically no pressure left to the nozzle.For more details you can refer above.
Q2. How can I know that the unloader valve is bad?
Ans. An unloader valve that has failed can create high pressure at the nozzle. The water is re-circulated by the unloader valve to the pump inlet while the pump is in operation but the spray wand is not in use.
Q3. Why my pressure washer dies when trigger is released?
Ans. The unloader valve is designed with a mechanism that works to divert the water-flow into the pump system in a loop. This happens when the user lets go off the trigger of the washer.
The engine stalling is the result of a bad unloader valve and this happens due to the increased pressure in the pump which is more than the engine’s power to rotate the pump.
Q4. Is it ok to self-install an unloader valve?
Ans. As per the experts and experience of many users, any sort of replacement or adjustment of unloader valves should only be performed by a dealer or a dealer who is experienced enough otherwise wrong installation and adjustment errors may trouble you later.