A pressure washer is a mechanical device that uses a high-pressure water jet to clean surfaces and objects like buildings, vehicles, and concrete. Pressure washers have become a popular cleaning tool for both residential and commercial use due to their ability to quickly and effectively remove dirt, grease, mold, and other debris. Most pressure washers have 3 main valves that control the flow of water through the machine – the inlet valve, unloader valve, and trigger valve.
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Inlet Valve
The inlet valve is located where the garden hose connects to the pressure washer. This valve controls water flow into the pressure washer. When the inlet valve is open, water from the hose can enter the pressure washer. When it’s closed, no water can get in. The inlet valve may be a simple manual valve that twists open and closed. On other models, it may be an electric solenoid valve that is opened and closed electronically using a switch on the machine.
The inlet valve serves a couple important functions:
- It allows the user to easily turn on and shut off the water supply to the pressure washer.
- It prevents water from entering the pressure washer when the machine is not in use.
- It enables the pressure washer to build up pressure – with the inlet valve closed, the pump can recirculate water within the washer to reach high pressures.
The inlet valve should always be closed when the pressure washer is not being used. This prevents water from passing through the system and leaking out of nozzles or fittings while idle. The valve should also be closed if the engine or motor is started with no water flowing. This protects the pump from damage due to overheating.
Unloader Valve
The unloader valve, also called a pressure relief or dump valve, is a key safety component of pressure washers. It regulates the pressure in the discharge line and protects the pump from excessive pressure. The unloader valve is typically located between the pump outlet and the discharge hose.
Here are the key functions of the unloader valve:
- Relieves excess pressure – If pressure in the discharge line exceeds the valve’s preset limit, it will open to route water back to the inlet side of the pump. This relieves the over-pressure condition.
- Bypasses water when idling – When the trigger gun is closed and not spraying water, the unloader valve routes water back to the pump inlet instead of letting the full pressure build up in the discharge plumbing. This allows the pump to continue rotating without deadheading and overheating.
- Aids in starting – The unloader valve makes it easier for the pump to start moving water at initial startup. Without it, the pump would have to work against the full discharge pressure.
The unloader valve spring tension or pressure limit is adjustable on some models. Adjusting the unloader valve affects the pressure washing performance. Increasing the pressure setting increases the discharge pressure, while decreasing it reduces the maximum pressure but enhances flow rate.
Trigger Valve
The trigger valve, also called the trigger gun valve or spray gun valve, controls the flow of water through the spray nozzle. It’s located on the trigger handle of the spray gun. When you pull the trigger, it opens the valve and water flows through the nozzle. Releasing the trigger closes the valve and stops the water.
The trigger valve serves a couple key purposes:
- It allows the operator to control when water is sprayed through the nozzle by operating the trigger.
- It provides a safe shutoff when the spray gun is not in use. This prevents unintended spraying.
On some pressure washers, the trigger mechanism directly actuates the valve internally. On others, it operates an electric solenoid valve. Electrically actuated trigger valves allow for features like variable pressure control through the trigger.
The trigger valve should close securely when released. Leaks in the valve can make the spray gun difficult to control and waste water. If the trigger valve becomes worn out, replacement of the entire trigger gun assembly may be required.
Chemical Injection Valve
Some pressure washers, especially larger or more expensive models aimed at commercial use, include an additional valve for injecting and siphoning cleaning chemicals or detergents. This chemical injection valve connects near the pump outlet and allows the chemicals to be mixed with the high-pressure water jet.
The chemical injection valve serves several purposes:
- Allows cleaning chemicals to be applied to the surface during washing. The chemicals enhance the cleaning performance.
- Adjusts the dilution and application rate of chemicals.
- May inject downstream near the discharge nozzle or upstream nearer the pump.
- Reduces the amount of chemicals needed for cleaning tasks.
Chemical injection valves vary widely in design from simple manual valves to electronically controlled solenoid valves. The chemical concentrate must be diluted properly for optimal cleaning and to prevent damage to the pressure washer components. Always follow chemical manufacturers’ recommended dilution rates.
Thermal Relief Valve
Some hot water pressure washers and steam cleaners include a thermal relief valve near the heating coil. This valve discharges water or steam if the temperature exceeds a preset limit to prevent dangerous overheating. The thermal relief valve is an important safety device on heated pressure washers.
Key functions of the thermal relief valve include:
- Senses water temperature and opens when it exceeds a fixed temperature limit, usually 190-220°F.
- Discharges hot water or steam until the temperature drops below the limit.
- Prevents pressure buildup and explosion risk if the heating coil malfunctions.
- May connect to a discharge hose or pipe to safely divert steam and hot water away.
The specific temperature relief point will be optimized for the type of cleaning system. Hot water washers require a lower limit around 190°F to prevent scalding. Steam cleaners necessitate a higher limit near 220°F.
The thermal relief valve should not discharge water or steam during normal operation. Leakage may indicate a problem with the valve or heating system. Proper maintenance and replacement of old valves reduces risk of overheating failures.
Nozzle Valve
The nozzle valve controls water flow at the very end of the high pressure hose where the nozzle connects. It allows different spray nozzles to be attached for varying spray patterns and flow rates.
Key features of the nozzle valve include:
- Located at the end of the discharge hose.
- Provides connection point for different nozzles.
- Seals against leaks when nozzle removed.
- Adjusts water jet pattern and pressure via different nozzles.
- Usually a simple male/female quick connect.
Nozzle valves are quick connection points that allow for easy nozzle changes. Common types include quick connect, bayonet, and threaded connectors. The nozzle valve should form a tight seal when closed to prevent water leakage.
Swapping nozzles enables selecting the best spray pattern for the job. Narrow high-pressure jets cut through tough dirt. Wide fan spray nozzles provide gentler cleaning over larger areas. Rotary and turbo nozzles create a rotating jet for increased performance.
Pressure Regulation Valve
Some pressure washers have an additional valve specifically for regulating pressure. This lets the operator adjust the water pressure for different cleaning tasks and surfaces. The pressure regulation valve provides more precise control compared to just changing nozzles.
Key attributes of the pressure regulation valve include:
- Located between the pump and discharge hose.
- Adjustable to set water pressure within a defined range.
- Locking feature maintains selected pressure during operation.
- Adjusting allows pressure optimization for cleaning application.
- Avoids damage to sensitive surfaces from excessive pressure.
The pressure regulation valve complements the unloader valve. The unloader mainly acts as a safety relief valve while the regulation valve allows adjustable operating pressure for different needs. Some models combine both functions into a single adjustable unloader valve.
Being able to fine tune pressure output allows optimal cleaning effectiveness while avoiding surface damage. Lower pressures around 800 PSI can be used for more delicate cleaning. Higher pressures near 3000 PSI are suited for tough dirt removal.
Conclusion
Pressure washers are equipped with several key valves to control the high-pressure water flow and ensure safe operation. The main valves found on most units include the inlet valve, unloader valve, trigger valve, and nozzle valve. More advanced models may also have specialized valves for chemical injection, thermal relief, or pressure regulation.
Understanding what the valves do allows properly operating and maintaining a pressure washer. Valves should be inspected and replaced as necessary to prevent leakage and ensure they continue functioning as intended. Always consult the owner’s manual for specific valve descriptions and servicing procedures on your pressure washer.
| Valve Name | Location | Purpose |
|---|---|---|
| Inlet Valve | Garden Hose Connection | Controls water supply into pressure washer |
| Unloader Valve | Between pump and discharge hose | Regulates pressure by relieving excess |
| Trigger Valve | Trigger gun handle | Controls water spray through nozzle |
| Nozzle Valve | Discharge hose end | Connects different spray nozzles |
| Chemical Injection Valve | Near pump outlet | Injects cleaning chemicals into water |
| Thermal Relief Valve | Near heating coil | Discharges hot water if overheated |
| Pressure Regulation Valve | Between pump and hose | Adjusts pressure for varying needs |