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SIMPSON

Simpson 4200 PSI Gas Pressure Washer, 4.0 GPM Commercial Power Washer, Cold Water, Honda GX390 Engine, 50' Hose, Aluminum Series, 49-State Compliant (ALH4240)

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Availability: In Stock.
Fulfilled by Amazon
Arrives May 25 – Jun 8
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Style: 4200 PSI


Features

  • SIMPSON PRESSURE WASHER FOR PROFESSIONALS: The Simpson Aluminum Series gas power washer cleans decks, driveways, siding, fencing, equipment, and graffiti; The cold water machine is great for contractors; 49-State Compliant (Not for sale in California)
  • ENGINE & PUMP: HONDA GX390 engine starts easily & includes low-oil shutdown; 4200 PSI 4.0 GPM CAT triplex plunger pump includes thermal relief to prevent overheating; Advanced oil seal technology & ceramic coated pistons extend seal life
  • LONG HOSE REACH: The Simpson Monster series 50' dual-braided high-pressure hose resists kinks and abrasion; Non-marring polyurethane jacket helps protect finished surfaces; Threaded M22 pump/hose connection
  • EASY MOBILITY: 13" premium pneumatic tires roll smoothly over gravel, grass, and curbs; Balanced layout improves transport; Aircraft grade aluminum frame with powder-coated finish is easy to assemble and resists corrosion; 38" L x 23.5" W x 29" H; 133 lb
  • PRO PRESSURE WASHER ACCESSORIES: Five quick-connect pressure washer tips (0, 15, 25, 40, and soap nozzle) cover tasks from stripping paint to car cleaning; Professional QC spray gun with safety lock-out and 16" spray wand included

Description

The SIMPSON Aluminum Series pressure washer 4200 PSI at 4.0 GPM is great for construction, equipment upkeep, and facility and fleet maintenance cleaning. With a powerful HONDA GX390 engine, reliable CAT triplex pump, and ultra lightweight aircraft grade aluminum frame, this pressure washer is the optimum blend of maneuverability and performance. The ALH4240 also comes with a 50’ hose, ergonomic spray gun, and 5 Quick Connect nozzles. Designed to meet the rigorous demands of the cleaning professional, the SIMPSON Aluminum Series frame is crafted of 100% aircraft grade aluminum, making it lighter in weight than most steel frame pressure washer designs. Perfect for contractors who specialize in deck cleaning, wood restoration, paint preparation, graffiti removal and all other professional cleaning services. The SIMPSON Aluminum Series designed for optimum performance in the harshest environments. Easy-to- assemble and easy-to-start, the Aluminum Series power washer is great for contractors who specialize in deck cleaning, wood restoration, and all professional services. 10 Year Limited Frame Warranty, 5 Year Limited Pump Warranty, 3 Year Limited Engine Warranty. Includes: Pressure Washer, Hose, Gun, Wand, 5 Quick connect nozzle tips, Detergent siphon tube with filter, Engine Oil, Quick start set up guide, Owner's manual.

Brand: SIMPSON


Power Source: Gasoline


Color: Red


Item Weight: 124 Pounds


Hose Length: 50 Inches


Product Dimensions: 38"L x 23.5"W x 29"H


Tank Volume: 2.5 Gallons


Maximum Flow Rate: 4 Gallons Per Minute


Global Trade Identification Number: 45


Maximum Pressure: 4200 Pound per Square Inch


Item Weight: 124 Pounds


Hose Length: 50 Inches


Item Dimensions L x W x H: 38"L x 23.5"W x 29"H


Tank Volume: 2.5 Gallons


Wand Length: 31 Inches


Power Source: Gasoline


Maximum Flow Rate: 4 Gallons Per Minute


Maximum Pressure: 4200 Pound per Square Inch


Color: Red


Brand Name: SIMPSON


Model Number: ALH4240


Global Trade Identification Number: 45


UPC: 879399001345


Manufacturer Warranty Description: Warranty Details Engine - 3 Year Limited Commercial Warranty | Pump - 5 Year Limited Warranty | Frame - 1 Year Limited Warranty


Manufacturer Part Number: ALH4240


Included Components: Aluminum 4200PSI,4.0GPM,Gas GX390


Unit Count: 1.0 Count


Item Type Name: Gas Pressure Washer, 4.0 GPM Commercial Power Washer, Cold Water, Honda GX390 Engine, 50' Hose, Aluminum Series, 49-State Compliant (ALH3228-S)


Manufacturer: SIMPSON


Frequently asked questions

If you place your order now, the estimated arrival date for this product is: May 25 – Jun 8

Yes, absolutely! You may return this product for a full refund within 30 days of receiving it.

To initiate a return, please visit our Returns Center.

View our full returns policy here.

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Similar Products

Top Amazon Reviews

    • This thing is a beast!
Style: 4200 PSI
I read a LOT of reviews here on Amazon and other online resources before deciding to make such a sizable investment in this 4200 PSI/4.0 GPM machine. This is not my first pressure washer, but my third actually. Each time I upgraded in both PSI and gallons per minute. This is my first pressure washer that is categorized as commercial use. Having finally taken the time to put this machine to the test, I can honestly say this thing has more than enough power to satisfy the average homeowner or DIY’er. As I said in the title: this thing is a beast! Mine arrived complete and undamaged. Other reviewers reported scratches and dents but that was not my experience at all. Assembly was quick and easy. My shipment contained a quart of Amsoil synthetic 10W-30 for the engine crankcase but I have seen other reviewers that got their oil in a plastic pouch. Once assembled, the crankcase filled with the supplied oil, and the fuel tank filled 1/2 way, I hooked up the garden hose and bled the air out for 30+ seconds as recommended. Set the throttle to half-way and closed the choke and gave the starter a quick pull and it fired right up on the first attempt. After allowing the engine to run at partial throttle with the trigger open to keep the water flowing and the pump cooled for a few minutes, I increased the engine speed to approximately 3/4 and started cleaning the concrete patio as my first project with this unit. The pressure even at less than wide open on the Honda GX390 was more than enough to get the accumulated grime blasted off effortlessly. Next up, I connected my 15” surface cleaner which really sped up the process. The 4240 pressure and water flow are a perfect match for the Karcher 15” surface cleaner. With all of the positive attributes of this machine, there is one thing that I feel is a negative: the hose. It’s more than long enough for most jobs but the stiffness makes moving around with it a real challenge. Given the higher than average PSI capabilities of the ALH-4240 it’s not surprising that the pressure hose is more on the stiff side, but as others have commented, it would be a good idea to upgrade to a better hose. Honestly, at this price point, a better quality hose should come with it. Overall, the ALH-4240 is a great pressure washer that has all of the power that the average person could want for DIY use. The high PSI and GPM make short work out of even the toughest cleaning projects. Time will tell if it lives up to the Simpson advertised claims of dependability and reliability. ... show more
Reviewed in the United States on September 17, 2024 by Kenneth B.
    • Class of its own
Style: 4200 PSI
AWESOME MACHINE!! My delivery was excellent. Not one scratch or dent on the box or the machine. The assembly was so easy I just took my time and read the instructions carefully. Many nuts and bolts were loos so go over them all. The nut on the throttle was way too tight. The washer worked flawlessly on my back yard 28sq patio. So happy with my purchase. ... show more
Reviewed in the United States on April 17, 2026 by Patriotic purchaser
    • Good product, horrible delivery
Style: 4200 PSI
The delivery was horrible. The unit was on its side. Opened the box and the handle was bent and scratched probably from being in its side. Used a plier to bend the handle to make it fit. The unit itself works great but very disappointed that a 1,400 power washer has a bent and scratched handle from before I used it. ... show more
Reviewed in the United States on April 19, 2026 by Jeff Crompton
    • 5 Star Performance, Zero Star Packaging
Style: 4200 PSI
Review Image by Sam Vert
Review Image by Sam Vert
This is my first pressure washer and I wanted to get a good one. Sure, I could save some coin buying a lesser unit, but I didn't want to spend all weekend cleaning my driveway and patio. I'm glad I got the big one. Mine was slightly damaged during shipping; more on that later. After adding the included oil and filling the tank with fresh gasoline, I fed the pump some hose water and pulled the recoil starter. It fired right up, as a Honda should! I started off with the rotary head (rated for 4.0 GPM) and it immediately began to clear the scum from my driveway. The engine is well muffled for such a large displacement, by the way. The 50 foot hose is adequate for most residential needs, but adding a 100 footer to the accessories pile would help for cleaning off rockeries and brickwork around the backyard. This is the Evergreen State after all and moss is EVERYWHERE! Moss has met it's match with this unit, but I digress.. The 4500 PSI rated hose is of a 3/8" size, and it's burly but not too unwieldy; there is a price for power. I found the hose needs a bit of attention to deliberately lay out according to your intended cleaning path because loops and twists are not easily handled without setting down the wand, walking back to the problem and uncoiling it manually. Again, it's par for the course here. The big Honda 390 pushes 4 gallons per minute with serious authority; it's easy to get cavalier with the wand but care must be used when getting close to wood as it will tear it up in no time flat, especially with a turbo head. Reducing the pressure and flow with the regulator on the wand proved invaluable around delicate structures and planter areas; I can't imagine using this machine without it. I really love the aluminum base and frame. It's nice to know that it will never rust and weight has been kept to a minimum. As for the CAT pump, what's not to like? Industrial duty and rebuildable, it's the best money can buy. And when it comes to pressure washers, it's really all about the pump. I can also say that if your plans for a pressure washer consist primarily of auto or boat washing, this unit is overkill extreme. An electric Karcher or similar machine would be much better suited to you. If you value your time as much as your money and want to spend more of it enjoying your property then cleaning it, this is the one to get! Now about the damage. The courier that delivered the box to my house had noted that they received it with the cardboard already torn and plastic shipping wrap bandaging up the sad sight. A brief inspection didn't show anything wrong, but as soon as the courier left, I noticed the frame had gotten bent and the handle wouldn't slide on. I decided to just bend the post back in place enough to slide the handle on and live with it. Thankfully the engine proper didn't sustain any blows. I've given the unit 5 stars because I think it deserves it, but Simpson has got to do something about their packaging. It's totally inappropriate to ship a 1300 dollar 125 pound machine in a 2 dollar single corrugated cardboard box. The machine was essentially swimming in a paper sack by the time it made it to my driveway. The wand and tube were simply dropped in the box without any extra protection and the fact that they weren't damaged or missing is nothing short of a miracle. In summary, I would say that if you order one of these, you're rolling the dice when it comes to damage. Be prepared to refuse the shipment or hassle with aftermath from a significant impact. ... show more
Reviewed in the United States on June 18, 2017 by Sam Vert
    • Built To Last
Style: 4200 PSI
Review Image by stevem
Very powerful, easy to move high quality throughout. I love the Honda Engine and CAT pump. Everything is built to last. Recommended!
Reviewed in the United States on April 9, 2026 by stevem
    • An extremely powerful unit
Style: 4200 PSI
This thing is a beast! I had a smaller unit for years, but beware this is a large very powerful unit. It arrived in perfect shape and operates smoothly. If high pressure, high water flow is what your looking for, this unit will fit the bill. Definitely commercial quality…
Reviewed in the United States on April 20, 2026 by Dan Ayo
    • Great power washer
Style: 4200 PSI
Does a great job. Has great power. I love the Honda motor. Recommend.
Reviewed in the United States on April 17, 2026 by Diane M.

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