Pounds Per Square Inch (psi) is the measurement of water pressure. The greater the psi, the better the cleaning efficiency.
Gallons Per Minute (GPM) refers to the water flow rate. Look for a combination of psi and GPM to deliver cleaning power. High pressure with little water flow is not effective.
Cleaning Unit (CU or UCE) is the water pressure multiplied by the water flow. A higher number means more power.
Gasoline engines are measured in horsepower (HP). Electric motors are measured in amperage (amps). More HP or amps means more power.
Pressure washers are available in a choice of two pump drive methods: direct drive and belt-driven. Heavy-duty belt-driven pumps offer more durability and efficiency.
The core of any pressure cleaning system is the high-pressure pump. Some pressure washers use plunger type pumps because of their high-pressure capability and compactness. More plungers result in smoother flow.
The actual cleaning is done by the nozzle or tip of the washer. The spray angle of the nozzle is adjustable to fit the cleaning need. The wider the spray, or fan, the lower its ability to cut through dirt. A zero-degree nozzle provides intense power. Fan angles of 15 to 25 degrees cover larger areas, combining stripping and washing power. Fans of 40 degrees or more are generally used for simple washing. Rotating nozzles are used for some cleaning applications.
