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Kärcher pressure washer

Pressure washers

Last updated: July 1, 2008.

You've tried water. You've tried soap. You've tried scrubbing and scouring. You've tried nasty chemicals that don't do what they say. So what do you do when it won't come clean? Roll out the pressure washer! Many people are now using these powerful cleaners to blast things clean with water jets pressurized at about 100-200 times the pressure of the air around us (that's 1500-3000 pounds per square inch or psi). They're brilliant on patios, drives, lawn furniture, barbecue grills, and all kinds of other outside grime. Let's take a closer look at how they work.

Photo: A small Kärcher pressure washer suitable for home use. Other popular makes include Ex-Cell™, Generac, Husky, and Honda.

Why pressure jets get things cleaner

There's a good scientific reason why water gets things so clean: its molecules have a slight electrical polarity (one end is positively charged and the other is negatively charged), so they tend to stick to things all by themselves. Detergents (soap chemicals) help water to do its job even better by breaking down gunge and grease and making it easier for water to flush away. But some kinds of ground-on dirt just won't budge, no matter how hard you try. That's when a pressure washer comes in really handy. It uses a narrow, high-pressure, jet of hot or cold water to blast dirt free. Because the water is travelling fast, it hits the dirty surface with high kinetic energy, knocking dirt and dust away like a constant rain of tiny hammer blows. It's only water, though, so it doesn't damage most hard surfaces. Having said that, it's a good idea to test a pressure washer on an inconspicious area before you start work to make sure it doesn't harm the surface you're cleaning. Always read the instructions before you use a pressure washer!

Parts of a pressure water

A pressure washer is less sophisticated than it sounds. It's really just a water pump powered by an electric motor. The washer takes in ordinary water from a faucet (that's a tap to you folks in the UK), the pump accelerates the water to high pressure, and then squirts it from a hose at speed through a trigger gun. You can fit various other attachments to the end of the hose for cleaning different things.

Kärcher pressure washer

Photo: The trigger gun from a Kärcher pressure washer. The hose runs up inside the plastic casing, through a valve, and out of the open end on the right.

These, then, are the main parts you'll find inside a pressure washer:

Some pressure washers have additional features. Water and electricity are not a good mix, so many power washers have ground-fault circuit breakers (also known as residual current devices or RCDs) built into the power supply to protect you in case of an electrical fault. Most washers work in the same way and do exactly the same kind of thing, but the more expensive ones tend to operate at higher water pressures (and have better cleaning power).

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