Difference Between The Thermal Relief Valve And Unloader Valve


If you’re a power washer owner, you’ve probably noticed that your pressure washer’s pump has an unloader or thermal relief valve. What’s the difference between the two? Here’s an explanation. These two parts of the pump are often interchangeable. The pop-off valve is the pump’s safety valve. It’s plumbed on the high-pressure side of the pump and is set at 300 PSI above the unloader.

Thermal relief valve

A pressure washer thermal relief valve is an essential safety device that keeps the pump cool during hot water use. These valves are available in different PSI settings and can protect the pump and heater from damage. Most major pressure washer brands come with thermal relief valves as a standard safety feature. A thermal relief valve opens when the pump reaches a certain temperature. This will prevent damage to the pump and heating coil, as well as the hoses and trigger guns that are often used with hot water pressure washers.

The thermal relief valve is installed in gas-powered pressure washers to protect the pump from overheating. Running the washer in bypass mode, which prevents water from flowing through the machine, can cause the pump to overheat and damage its components. A thermal relief valve plumbs into the pump inlet, and when the temperature reaches 145 degrees F, it opens. The cool water will enter the pump, reducing the temperature inside the pump head.

Unloader valve

The unloader valve on your pressure washer is one of the most common areas for trouble. These mechanical parts can fail due to many different reasons, including over-adjusting them or not using enough water. If this happens, you may need to replace your unloader valve or install a new one. In both cases, the repair or replacement process may take some time. Here are some steps to take to extend its service life.

To begin the repair process, remove the unloader valve. The valve should be free from debris. If the valve is stuck, you can remove it with a small pick. Then, remove the adjusting knob and clean out the blocked pore. Once the pore is clean, replace the spring and O-rings. To replace the unloader valve, follow the same process as before. Ensure that the valve is properly lubricated.

Secondary control chamber

The secondary control chamber of a pressure washer relief valve is a simple design incorporating a spring and a diaphragm. The diaphragm is divided into two sections, with the upper section serving as a seat 64 and the lower section as a valve. The chambers are connected by a flexible tube 17 and a check valve 19 is interposed between them. The spring and the valve are biased to a closed position, and the valve prevents the second liquid from flowing into the port.

The primary control chamber of a pressure washer relief valve is a gear-type pump that displaces high-pressure fluid to the outlet 65. The pump and the valves are mounted to a frame and support a fluid reservoir. Pump 25 is powered by an external source, and a pump hose is attached to the frame. Fluid is normally water, though soap-water solutions, ammonia, and other fluids are also used.


A pressure washer relief valve is a essential safety device that helps to keep the pump cool during hot water use. If you have a pressure washer, it’s important to check the condition of your relief valve regularly and replace it if necessary. Installing a new one is easy, and doing so can help to extend the life of your pressure washer.


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