Try this little experiment - go outside and turn on your water faucet.
In one minute, 8 gallons of water will pour out of your hose.
Now, attach a spray gun to your garden hose.
You basically reduce the flow to about 5 gallons per minute. As a result, the water pressure increases from 10 PSI (pounds per square inch) to 40 PSI.
This increases the pressure by 4 times and simultaneously reduces the amount of water used. However, the water pressure isn’t strong enough to actually clean anything. It just pushes stuff around and gets your socks wet.
A pressure washer takes the same principle to the extreme; it uses a gas-powered engine or an electric motor to boost water pressure to 1000-4000 PSI. We’re talking about serious water pressure that can actually clean stuff.
Understanding Our Language
Pounds per Square Inch (PSI)
The first step for selecting a pressure washer is determining which grade you fall into:
Water pressure is measured in PSI. The PSI is necessary to break the chemical bond between the surface and the stain. The stronger the chemical bond – the more pressure you’ll need to remove it.
Gallons Per Minute (GPM)
Water flow is measured in GPM. The larger the GPM, the more surface area a pressure washer can clean.
Cleaning Units (CU)
The true test of a pressure washer is measured in Cleaning Units. Imagine two streams of water under the same amount of pressure. The first stream contains twice the water as the second. As a result, it will clean twice as fast.
Calculate the CU by multiplying the PSI times the GPM. (PSI x GPM = CU)
We can't all be Bob Vila; but that doesn't mean you shouldn't take pride in keeping your home looking its best. Consumer pressure washers are very affordable and are built for the DIY-er out there.
Consumer pressure washers are equipped with a consumer engine as well as a consumer-grade pump. What this means is they are not designed to be used everyday, rather for the homeowner looking to wash their car weekly, or to clean their siding in the Spring.
Semi-pro power washers bridge the gap between consumer and professional units. These are equipped with either a professional pump and a consumer engine, or a professional engine and a consumer pump.
For folks who take home upkeep more seriously than just a pesky chore, semi-pro pressure washers are for you. They are designed to handle frequent use so you can clean to your heart's content on a regular basis.
If you look at the chart above, you'll notice the low ends of the different grades have similar numbers. So what gives? Well, the PSI, GPM, & CU may be similar, but that's not what a professional pressure washer is about.
Professional power washers are built with a professional engine, as well as a pump. This means the pump is designed to run for many more hours than a consumer pump. What this means for you is you can use a professional unit everyday. If you do that with a consumer unit, the pump will burn out much faster.