A pressure washer is a mechanical sprayer that uses high-pressure water to clean and remove mold, grime, dust, mud, and dirt from surfaces and objects such as buildings, vehicles, and concrete road surfaces.

Equipment can be rented or bought that produces pressures from 50 bars (750psi) up to 1200 bars (30,000psi) or more. A pressure washer differs from a parts washer in that a parts washer typically uses high-volume, low-pressure (20-150 psi) cleaning solutions in an enclosed cabinet to clean dirty parts.

The most basic pressure washer consists of:

• A motor which directly drives a water pump
• High-pressure hose
• Trigger gun-style switch

Just as a garden hose nozzle is used to increase the outflowing dynamic pressure of the liquid, a pressure washer adds its own power to force high-dynamic pressure.

Note that the pump does not draw more water from the pipe to which the washer is connected than that source can provide; therefore, the water supply must be adequate for a given machine to be connected to it: its flow must be equal or superior to that of the washer, so that the pump is never starved (which can damage it).

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, while others emit a pencil-thin jet of water, which spirals around rapidly. 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 low-pressure injector that introduces the chemical after the water leaves the pump (a downstream injector) and a high-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.