When your system uses a trigger gun that stops the water flow from the pressure pump the unloader valve must be employed.
Understand that when the trigger of the gun is released the water flowto the nozzle is interrupted. The power source and the pressure pump are still running, Without some pressure washer system safety device the water would have nowhere to go, building pressure till disaster ensued.
Enter the Unloader Valve
The most basic function of the unloader is to act as a "traffic cop" to the water flow in your system. Depending on the type of valve it will either sense "pressure build" ór "reduction in flow".
Depending on the type, when one of these conditions is met the unloader will then actuate to divert the water flow back to the inlet side of the pressure pump.where it will circulate through the pump back to the inlet side of the valve to the inlet side of the pump again in what is called a bypass loop when this is occuring the pump is said to be in "bypass mode" and the unloader valve is said to be "cycling". This scenario ends when the trigger is squeezed alerting the unloader valve to redirect the flow to the high pressure nozzle once again. While this may seem to be problem solved it is not without risks. When the water flow is in bypass new cool water is not entering the system. The moving parts in the pump are creating friction which produces heat that is transferred to the water flow in bypass. Since a limited amount of water is in bypass this transfer of heat can occur quickly.
Most pumps are designed to handle water temperatures of 140 F. When the water in bypass reaches 155 F damage to the pump will begin. Damage can occur to the pump packings, plungers and seals and even to the short bypass hose in external bypass setups. It is a good idea to have a pump with a thermal relief valve to offer some protection against excessive heat build up. It is a better idea not to leave a pump in bypass mode for more than 2-3 minutes, by simply squeezing the trigger gun you will introduce new cool water into the system.
There are two basic types of pressure washer unloader valves.
"Trapped Pressure " These are commonly referred to as just"Pressure" type.
This type of valve opens to bypass when it senses the pressure build up of the pump output having nowhere to go. The main characteristic of this the most commonly used valve is how it traps the pressure in the hose when the trigger of the pressure gun is released.
The disadvantage of this type of valve is the spike of pressure felt by the operator and pressure washer components when the trigger is again squeezed. This creates a "kickback" effect on the gun/wand so be careful when using ladders or other types of access equipment.
The next type of unloader is the "flow" type unloader valve
this type of valve actuates the bypass loop when it senses the lessening of flow between the valve and trigger gun. The main charachteristic of this valve is that no pressure is trapped in the hose thereby eliminating the pressure spike created by the "trapped pressure" valves.
The main disadvantage of the flow type unloader is that you can't change the pressure by downsizing the orifice size of your nozzles. The valve senses the loss in flow and begins to cycle repeatedly.
The Compensating Type Unloader Valve
The most recent addition to the world of unloaders is the compensating type unloader. This concept is a hybrid between the flow and trapped pressure unloader types. Basically this is a trapped pressure unloader with a compensating feature which radically lessens the pressure spike typically felt with the standard trapped pressure unloader. The concept of this unloader is to have the smoothness typical of a flow type unloader without the inherent disadvantages.
These are the unloader valves used in the industry today. As with any of these articles. If you have a question we haven't answered please don't hesitate to submit a question to us. You can find the submita question form by hitting the submit a question button found on the bottom of the home page navigation bar. This helps us to create a more useful resource for you and it's always great to know there's real people out there!