- 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) is the water pressure multiplied by the water flow. A higher number means more power.
- Gasoline engines are measured in horsepower (HP). More HP equals more power.
- Electric motors are measured in amperage (amps). More amps equals more power.
- Direct drive is a shaft driven pump directly off the engine or motor. Requires less maintenance although when something does go wrong, typically more expensive to fix.
- Belt drive uses a set of pulleys and a v-belt or a cogged belt to drive the pump. Although belts can break, they are less prone to expensive mechanical repairs.
- Plunger type pumps typically have high-pressure capability with great serviceability and pump life. More plungers results in a smoother flow.
- Radial axial pumps are usually lower pressure pumps used on lighter-duty equipment.
- The nozzle or tip of the washer does the actual cleaning work. 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 (also called turbo nozzles) are used for heavy duty cleaning applications.