Unloader Valves

Every hot or cold pressure washer needs an unloader or bypass valve to recirculate and relief the pump from load when the trigger is in the closed position. The unloader or bypass valve also prevents safety hazards and possible accidents.

The unloader or bypass valve prevents :

• Pump damage
• Motor start-up faults
• Blowing fuses

The Unloader Valves have a check valve in the outlet to avoid high-pressure water returning to the tank. They can also have pressure switches, flow switches and pressure gauges retrofitted.
A Pressure Microswitch is activated when the gun is open or closed. These can be wired differently depending on the control system used. This Microswitch will then tell the PCB to start or to stop the pressure washer. Karcher uses this feature on the domestic and larger machines. The machine will then reactivate as soon as the operator presses the trigger. This is called a trapped Pressure Unloader.

Zero Pressure Unloaders K-SERIES

Zero Pressure Unloaders usually have a timer (control) but this is not essential for the machine to operate. The machine will time out after 2 mins in bypass (pre-set time). This is called "Total Shutdown" and the machine will then need restarting on the main switch after the time has elapsed. This type of unloader valve (K-SERIES) has zero pressure in the hoses. All the water is pumped back to the inlet or header tank. Manufactures such as DTE and Dirt Driver, prefer this system as the machine will never surge (intermittent stop-start).

Trapped Pressure Unloader Valve

A common unloader valve on Pressure Washers is the VB9 and VRT range that we also sell. These hold the trapped pressure in the hose to the gun and lance when the machines time out. It will typically sit in standby / idle and will only restart if there is a pressure drop in the high-pressure line. A drop of 10 bar will make the machine start/stop as the pressure drops in and out. This is where and how common leaks are detected. If the machine surges too many times, the PCB will shut the system down completely.

The advantage of a trapped Pressure Unloader Valve is being able to restart the Jet Washer by pressing against the trigger. This, therefore, prevents the user from having to travel to the machine multiple times to activate it.

Due to the rate of high-pressure and volume of water, the Unloader Valve starts to wear along with the Lance Nozzle. This wearing of the Unloader Valve has a significant result on the pressure. Often you will find low pressure and fluctuating. Repair Kits are available in addition to complete Unloader Valves.