A pressure washer is a high pressure mechanical sprayer that can be used to remove loose paint, mold, grime, dust, mud, and dirt from surfaces and objects such as buildings, vehicles, concrete surfaces, etc. The volume of a pressure washer is expressed in either gallons or litres per minute, often designed into the pump and not variable. A pump's pressure, expressed in pounds per square inch, pascals, or bar (deprecated but in common usage), is also designed into the pump but can be varied by adjusting the unloader valve. Machines that produce pressures from 750 to 30,000 psi (5 to 200 MPa) or more are available.
The basic pressure washer consists of:
- An electric motor or gasoline (petrol) engine that directly drives a water pump
- A high-pressure hose
- Trigger gun-style switch
Similarly as a garden hose nozzle is used to increase the velocity of the liquid, a pressure washer adds its own power to create high pressure and velocity. The pump cannot draw more water from the pipe to which the washer is connected than that source can provide. Moreover, the water supply must be adequate for a given machine connected to it, as water starvation leads to cavitation damage of the pump elements.
Several different types of nozzles are available, each useful for a particular application. Some nozzles cause the water jet to be ejected in a triangular plane (fan pattern), while others emit a thin jet of water, which spirals around rapidly (cone pattern). Nozzles that deliver a higher flow rate lower the output pressure. Most nozzles attach directly to the trigger gun.
Some pressure washers, in combination with a particular nozzle, allow detergent to be introduced into the water stream, assisting in the cleaning process. Two types of chemical injectors are available — a high-pressure injector that introduces the chemical after the water leaves the pump (a downstream injector) and a low-pressure injector that introduces the chemical before water enters the pump (an upstream injector). The type of injector used is related to the type of detergent used, as there are many chemicals that will damage a pump if an upstream injector is used.
Pressure washers are dangerous tools and should be operated with due regard to safety instructions. The water pressure near the nozzle is powerful enough to strip flesh from bone. Particles in the water supply are ejected from the nozzle at great velocities. The cleaning process can propel objects dislodged from the surface being cleaned, also at great velocities. Pressure washers have a tendency to break up tarmac if aimed directly at it, due to high pressure water entering cracks and voids in the surface.
Most readily available consumer units, commonly found online or at hardware stores, are electric- or petrol-powered. The electric ones plug into a normal outlet, use cold tap water and typically deliver pressure up to about 2,000 psi (140 bar). Petrol powered units can often deliver twice that pressure, but due to the hazardous nature of the engine exhaust, they are unsuitable for enclosed or indoor areas. Some models can generate hot water, which can be ideal for loosening and removing oil and grease.
Read more about Pressure Washer: Origin, Uses, Types, Specialty Washers
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