Choosing a Pressure Washer

With so many factors at play from multiple power measurements to nozzle designs, picking out a pressure washer can be confusing. This breakdown will help you understand what all these numbers and choices mean, so you can find a machine that fits your needs.
Power: GPM, PSI and CU
There are three measurements for pressure washer power:
– Pounds per Square Inch (PSI) is the amount of water pressure
– Gallons per minute (GPM) is the amount of water coming out of the nozzle
– Cleaning Units (CU) is GPM multiplied by PSI
Cleaning power depends on both pressure and volume, so CU gives you the best picture of the washer’s performance. This is easy to overlook, since most residential pressure washers emphasize PSI. For example, let’s say you’re comparing Vortexx’s light duty pressure washers. If you look at PSI, they seem to be about the same. However, there’s a big difference when you factor in volume.
2700LD: 2,700 PSI x 2.5 GPM = 6,750 CU
2750LD: 2,750 PSI x 3 GPM = 8,250 CU
The 2750LD makes only 50 more PSI than the 2700LD, but thanks to a flow rate increase of 0.5 GPM, it provides 22% more cleaning power.
Power Washer Nozzles: A Size for Every Job
Most pressure washers come with 5 nozzles.  The black nozzle can pick up detergent from the soap system and spray it on the surface you’re cleaning. The other four nozzles have different spray patterns from a 40 degree white nozzle to a 0 degree red nozzle. Each nozzle has a specific cleaning use, from washing cars to removing rust and dirt from bare metal.
Concentrating the spray increases force, but it doesn’t increase cleaning power. If you use a nozzle with too small of an angle, you can damage the surface you’re cleaning. If you need more cleaning power, you need a pressure washer with a higher output.
Pump Design: Triplex or Axial
While there are several pump designs on the market, most pressure washers use either an axial or a triplex pump.
An axial pump uses an impeller to move water. This pump connects directly to the engine shaft. These pumps are cheap, but their output is limited. They also wear out quickly, so they’re mostly used in residential pressure washers.
A triplex pump has three pistons that move up and down to pump water. This pump design connects to the engine using a gearbox. By changing the gear ratios, the manufacturer can increase the pump speed to deliver more pressure. These pumps last a long time, so they’re great for commercial use.
Hot Water or Cold Water?
Hot water is more effective at cleaning than cold water, but it also makes buying and fueling the pressure washer more expensive. With the heater turned off, the machine works like any other pressure washer. Turn it on, and the hot water coming out of the nozzle cuts through grease, oil, glue and tar with ease. Hot water systems are a great choice for cleaning vehicles and heavy equipment. They’re also the only effective way to remove old chewing gum from pavement.
We’re More than Just Mowers
Shank’s Lawn sells and services all types of small engine equipment, including pressure washers. We’re a certified dealer for Cub Cadet and Vortexx pressure washers, and we service pumps from popular brands, including AR and Cat Pumps. If you’re looking for a new pressure washer, or you need help with your current unit, visit us at 4900 Molly Pitcher Highway in Chambersburg, PA.
We also ship factory parts and accessories across the United States and Canada. To order, visit our website,

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