Vehicle Washing

A guide to pressure washers and vehicle washing systems

“Portable hot water pressure washers with gasoline or diesel engines and heated by diesel are the choice for customers that need the ability to clean where water is readily available but electric power is not. These units are portable and self-contained and give the operator the ability to clean practically anywhere.”

For contract cleaners or customers that need to clean where water and power aren’t readily available, skid-style machines are available. Skids are self-contained units consisting of a gasoline or diesel engine, a belt-drive pump and heating coil.

Skids can easily be mounted to a trailer, box truck, van or other capable vehicle and can be plumbed to a large water tank (typically 200 to 500 gallons) for truly portable, on-site cleaning.


The question, how long will you be cleaning, “reaches the heart of how much quality you need in your pressure washer, which also affects the price tag,” Dunn says.

Most pressure washers, regardless of brand, have similar components. They have an engine or motor that turns a high-pressure pump. Hot-water models also have a burner that heats the water as it races through a coil made of pipe or tubing.

“The quality differences are not always obvious, but significant nonetheless,” he points out, and suggests asking seven insightful questions in order to identify quality in a pressure washer.

1. Is it belt-drive or direct-drive?

A high-pressure pump does not turn on its own, explains Dunn. It is driven by an engine or motor.

There are two predominant ways to connect the pump to an engine or motor: directly (direct-drive) or with a pulley and belt (belt-drive). Pumps generally turn at 1,100 to 3,600 rpm. Gasoline engines turn at a rate of 3,000 to 3,600 rpm. Electric motors turn at a rate of 1,450 to 3,450 rpm.

“Direct-drive pumps are more compact and more efficient since the pump is coupled directly to the motor or engine, so you can get more performance for the same input power,” he says. “Additionally, these units generally weigh and cost less.

“As you may expect, a pump turning at 3,600 rpm will wear out faster than a pump that turns at 1,500 rpm.

“On the other hand, a belt-drive pump, configured with a pulley and belt, allows the pump to turn at the slower rate - usually 1,500 rpm. The belt also dissipates the build up of heat and absorbs vibration from the engine.”

“The ultimate benefit,” notes Dunn, “is that downtime is minimized and the pump’s life is extended, saving money in the long run.”

2. What is the style of pump?

High-pressure pumps come in two major types: axial (sometimes called “wobble plate” or “swash plate” pumps) and crankcase pumps, he says. Axial pumps are only available in a direct-drive configuration, but have half as many moving parts as their crankcase pump counterparts.

Axial pumps work by the motor or engine turning a tapered plate inside the pump which directly moves the pistons of the pump to move the water produce pressure and flow. “Axial pumps can typically only achieve up to 5 gpm (gallons per minute) or 4,000 psi, but they are more efficient due to having fewer moving parts than crankcase pumps,” he points out. “Having fewer components in the pump means that there are fewer chances for an item to fail.

“One additional benefit to axial pumps is that due to having less items to move, you can achieve greater output performance than a crankcase pump with the same input power.”

Crankcase pumps are available in direct and belt-drive configurations and utilize a crankshaft, connecting rods and ceramic plungers.

Both styles of pumps come in various quality levels depending on price range.

3. Does it have high pressure or high volume?

“A little known secret is that there is more cleaning power in a pressure washer’s volume - gpm - than in its pressure - psi, says Dunn.

“A pressure washer with 2 gpm and 3,000 psi won’t clean as fast as a pressure washer with 4 gpm and 2,000 psi. The first pressure washer delivers 6,000 cleaning units (2 x 3,000) as compared to the second pressure washer’s 8,000 cleaning units (4 x 2,000).

“Volume is the deciding factor and a quality pressure washer will provide the proper balance of volume and pressure.”

4. Is the engine or motor size correct?

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