As the name implies, pressure washers use motorized pumps to force water at high speed through a hose. The resulting pressurized water often eliminates the need for harsh cleaning chemicals, degreasers, or detergents.
Rated in pounds per square inch (psi), a unit’s psi indicates its ability to break the contaminant-surface bond. Basically, the greater the psi, the better the washer can scrub the tough stuff.
But beware: The psi needed to peel paint is much greater than that for getting dirt off a fender. Too much psi could mean an unscheduled paint job.
Pressure isn’t everything
Flow is as important as pressure. The more gallons per minute (gpm) a washer produces, the more quickly it obliterates the caked-on mud from a road grader’s undercarriage.
As with pressure, however, flow alone doesn’t fully describe the cleaning prowess of a pressure washer. To get a clearer picture, multiply the psi and gpm to calculate cleaning units (CU).
For instance, a 3,500-psi machine operating at 3.8 gpm has 13,300 CUs. Considering psi alone, it looks more robust than a 3,000-psi model. But if the latter offers 4.5 gpm, it has 13,500 CU, or 200 more than the first option.
Next page: Flow’s not everything, either, Hot or not?