ALH4240 4200 PSI Commercial
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Powerful commercial pressure washer with a Honda engine, CAT industrial pump, and a wide cleaning radius

The Simpson ALH4240 Honda GX390 Pressure Washer has a very high PSI, which means it is very powerful. Combined with that 4200 PSI is a Honda engine, CAT-brand, high-pressure industrial pump, and a long hose. This pressure washer is best for bigger, tougher cleaning tasks like preparing decks and patios for paint or removing graffiti. Because commercial pressure washers tend to be bulky and heavy, the Simpson’s high-quality tires are also key to its overall convenience and effectiveness.

HONDA OHC engine

Like OHV (Overhead Camshaft) engines, the OHC-design on the ALH4240’s Honda GX390 engine is lighter and therefore more energy-efficient than other types of engines. This is because OHC engines don’t require as many parts. The fuel tank holds about 6.4 quarts of gas and generates 4200 PSI of power, which is one of the higher PSI’s available.

CAT industrial triplex pump

It’s important for your pressure washer’s pump to be both reliable and durable. The Triplex pump is a CAT-brand, and is designed to run cooler so it doesn’t wear down as quickly. It can also be rebuilt if necessary. It provides a lot of pressure and up to 4 gallons of water per minute, so cleaning large areas with lots of grime goes by more quickly.

Pro-Style gun and wand

All that powerful water comes out of the Dial-N-Wash spray gun. You can adjust the pressure from 1000 PSI to the full 4200 PSI so you have more flexibility about what and where you clean. Five Quick-Connect nozzles increase flexibility and versatility; you get a 0-degree, 15-degree, 25-degree, 40-degree, and soap applicator.


Superior tires

With a big commercial pressure washer like the Simpson Honda GX390, sturdy tires are very important. This washer has 13-inch, premium pneumatic tires that help keep the washer stable as you wash, and have better mobility.

More detergent options

Using soap as part of your cleaning process can be very useful. Unlike just water, soap can eat away at grease and grime. The Simpson ALH4240 has a downstream detergent injection system so you can choose from a wider selection of pressure washer-safe detergents.

Long, durable hose

Having a long, durable hose gives you a wide cleaning radius so you don’t have to spend time and energy moving the whole unit around. The hose is 50-feet and steel-braided, as well as kink-and-abrasion resistance.



At 124 pounds, the Simpson is pretty heavy. If you have trouble moving heavier items, you will definitely want to take advantage of the cart with wheels. This washer is lighter than washers with steel frames, so it isn’t as heavy as some other units.

Overall Review

The Simpson ALH4240 is a very powerful pressure washer packed with features, like an OHC engine, Pro-Style wand with nozzles, a long-lasting pump with high-pressure, and a wide cleaning radius. If your cleaning tasks include washing out livestock stables and commercial spaces, this is definitely a good pressure washer to consider for all your needs. Take full advantage of the cart with big wheels to take off some of the strain of the washer’s 124 pounds, though with the long hose, you have a lot of freedom to move about while you clean.