How to Select a Pressure Washer

A pressure or power washer works by the interaction of two elements:

1. Water pressure is measured in pounds per square inch (PSI). The PSI is is what breaks the chemical bond between the surface you're cleaning and the dirt or stain. The stronger the chemical bond – the more pressure you’ll need to remove it. Water pressure also helps you conserve water. An unpressurized garden hose can use 5-8 gallons per minute, while a pressure washer squeezes it down to about 3-5 gallons.

2. Water flow is measured in gallons per minute (GPM). The higher the GPM, the more surface area a pressure washer can clean. A pressure washer's cleaning power is measures in Cleaning Units (CU) which is a function of how much water flows through a given amount of pressure. The more water that can be pushed through the faster you can clean your surface even if the PSI is the same. For example if one washer moves two times the amount of water as another washer, it will clean twice as fast. You can calculate the CU by simply multiplying the PSI times the GPM (PSI x GPM = CU). This is a good way to compare machines when you're shopping.

Determining the right pressure washer for you depends on what you intend to do with it. Someone who just wants to wash the car and sweep the driveway has very different needs than the person who needs to clean roofs and siding. You want to buy the right machine for the job. Every cleaning job needs a certain amount of pressure to loosen the dirt from the surface, but you don't want to go overboard damage your surface. And getting a higher-PSI machine than you need will not speed up the job - using pressures greater than 20% over the minimum required to break the bond doesn't make cleaning go any faster and in fact can damage the surface. Once you get to the pressure point where the bond breaks, only increasing the water flow will decrease the cleaning time.

What Type?

Generally most pressure washers are either gasoline or electric. More specialized units use diesel, propane, oil, or hydraulic power. By looking at the table below to see what kinds of activities you want to use the washer for, it is easier to select a unit.

Electric powered washers are limited by the availability of electricity, but are lighter and quieter. A washer with a fuel tank gives you more flexibility and mobility, but the downside is that they can't be used indoors and they are noisy.

You also need to decide whether your jobs require cold or hot water. There are some jobs that need hot water to loosen the material from the surface - just pressure isn't enough. The pressure, volume, and horsepower relationships are equally important for both cold and hot water models. Cleaning solutions are also important in dissolving the dirt. However, oil and grease stains require hot water to separate the molecules from the surface. Hot water power washers are heavier than the cold water ones because of the burner which raises the water temperature to about 200 degrees Farenheit, and because of the extra features these high powered machines have. These include a fuel tank for 508 gallons of fuel, adjustable thermostat and pressure pop-offs, totally enclosed motors, powder coated frames, electronic ignitions, roto-molded tanks with automatic shut-offs if machine runs dry, etc.

Residential models are the least expensive washers you can buy new. The compromise is that they are less durable and are limited in the amount of cleaning they can do. Commercial quality units quite varied in their features (for example commercial models can range in PSI from 1100-7000 PSI and water volume 2.0-5.6 GPM output) and are likely to have units that will fit most needs. These units are better built with more durable pumps and other components and weigh between 80 and 300 pounds. They are much less expensive than industrial rated machines and are often the best blend of value, usability, and durability. If you are buying a used unit, you should factor in this information when deciding how much to pay. A used residential model may have a very limited life expectancy depending on how it was used! Used commercial units can represent excellent value and are well worth investigating.

Electric Pressure Washers

Generally speaking electric pressure washers come in two sizes: small (1300-1600 PSI) and large (1700-2000 PSI). However, it’s actually the type of motor that defines them.

Universal (or brush) motors are typically found in small, hand-carry pressure washers and perform the job at a very inexpensive price. If you rarely use your pressure washer, you can save some money by purchasing an electric power washer with a universal motor. It just won’t last as long.

Induction (or brushless) motors, however, are typically used in larger, more powerful electric power washers. They usually last longer than universal motors which means they also also cost more. If you're going to buy an electric motor that will perform more reliably and last longer, it's worth the extra cost to get one with induction motor.

Small Electrics - better than an Ordinary Garden Hose!
Small electric power washers (generally less than $100 new) are ideal for cleaning small surfaces, such as cars, garbage cans, grills and patio furniture. They are very easy to use. You just connect your power washer to your garden hose, plug it into an electrical outlet and start power washing. These power washers are strategically designed for easy maneuverability and storage. They’re light enough to carry by hand, and easily fit on a shelf, saving valuable floor space in your garage. On the downside, small electric power washers don’t normally come with detergent tanks. Instead, they have a siphon tube that draws detergent from a bucket or bottle. If you like using detergent, you should consider getting a larger one with a built-in detergent tank instead.

Gasoline Powered Pressure Washers

Direct Drive - The engine is connected directly to the pump. A shaft running from the engine into the pump is what drives this kind of configuration. Advantages: Lower initial cost of ownership. Fewer drive system components.

Belt Drive - The belt drive unit has the engine seperated from the pump. The belt assembly is what drives the pump. Advantages: Having the engine and pump seperated means less heat. Superior at absorbing the movement of the engine. The pump runs at half the speed of a direct drive unit. These three things contribute to the long life of a belt driven pump system.

A pressure washer can be a small or large investment depending on the unit you buy. Getting the right unit for the job is critical, because "More Power!" is not always a good thing and can cost you plenty in damaged items and surfaces. On the other hand, cheaply made poor-quality washers are a waste of money because they don't get the job done and you'll have to replace them more often if you use the machine regularly. Shop for value, get the right unit, and have fun cleaning!