Toeing the Line With Pressure Washers

A pressure washer takes water and makes it radical. Water enters one end of the machine at a pressure in the range of 30 to 80 psi and moves along at 4 mph.

- By Roy Berendsohn

A pump driven by a motor or engine boosts the speed of the water, which exits the machine at roughly 200 mph. And if you measure the pressure right at the nozzle, it can range anywhere from 1,000 to 3,000 psi.

That's key to understanding why pressure washers are so effective. Double the speed of the water, and you increase its kinetic energy by a factor of four. That's a lot of hitting power.

But it's also important to understand that it's not so much that the machine puts all that power at your disposal. It's in knowing how to use it.

HOW A PRESSURE WASHER WORKS

Water enters the pressure washer via a garden hose [a] and moves through a pump, which consists of a series of two or three plungers (b) arranged in a line or a circle. The plungers are powered by an output shaft on the engine or from a motor. Each plunger boosts the water pressure sequentially, one feeding higher pressure water to the plunger next in line. The last pulse of high-pressure water exits the pump. The water moves through a component called the unloader [c]. This component unloads water if it gets too hot because the gun's trigger is off. Next, the water travels down the hose to the gun [d]. When you pull the gun's trigger, you send a series of high-pressure pulses of water out the nozzle.