SIMPSON AAA Replacement Pressure Washer Pump 4400 PSI 4.0 GPM — Horizontal 1" Shaft, Stainless Unloader

The SIMPSON 90034 AAA triplex replacement pump delivers up to 4400 PSI at 4.0 GPM for horizontal-shaft gas pressure washers, offering a durable, easy-to-fit solution to restore high-performance cleaning.

This pump kit is engineered as a direct replacement for many gas-powered pressure washers that use a horizontal engine with a 1" shaft, including common models driven by engines like the Honda GX390. Built with heavy-duty internals and an integrated stainless steel unloader, the 90034 focuses on reliable flow and pressure while minimizing engine drag. It installs in minutes on compatible units and includes features intended to extend service life and simplify maintenance.

How does the 90034 improve everyday cleaning power?

The pump boosts nozzle pressure and maintains consistent flow so you can remove dirt, mildew, and grime more efficiently. PowerBoost technology amplifies force at the tip while an adjustable knob lets you dial pressure down for gentler tasks.

• Delivers up to 4400 PSI and 4.0 GPM for heavy-duty cleaning
• Adjustable hand knob for lower-pressure tasks
• PowerBoost increases effective nozzle pressure for quicker cleaning

Will the pump fit my pressure washer and how hard is installation?

The 90034 uses an SAE-standard bolt pattern and a 1" horizontal engine shaft, so compatibility hinges on matching orientation, shaft diameter, and the unit's inlet/outlet layout. Installation is straightforward for most mechanically inclined users; basic hand tools and alignment checks are usually all that's required.

• Fits many gas units with horizontal engines and 1" shaft
• Standard garden-hose inlet and quick-connect high-pressure outlet
• Confirm shaft size, bolt pattern, and inlet/outlet orientation before purchase

What design features support durability and easier maintenance?

Durable components reduce friction and wear while maintenance-friendly features let you monitor and preserve lubrication without hassle. The pump includes oversized ball bearings, a sight glass for oil visibility, and a stainless integrated unloader to protect the engine during bypass.

• Dual oversized ball bearings for reduced wear and long service life
• Sight glass eliminates the need for a dipstick and shows oil condition
• Stainless steel integrated unloader with easy-start functionality

Which hoses and accessories are compatible with this replacement pump?

The pump accepts standard garden-hose feed lines and quick-connect high-pressure outlets so it pairs with a wide range of common pressure-washer hoses and fittings. SIMPSON lists compatibility with several of its own hose lines, but many third-party quick-connect hoses will work as well.

• Garden-hose inlet for convenient water supply connection
• Quick-connect high-pressure outlet for standard pressure hoses
• Works with several SIMPSON hoses like Armor and Monster series

Who is this for: The SIMPSON 90034 AAA Professional Triplex Pump is aimed at homeowners, contractors, and rental shops that need to restore or upgrade a gas pressure washer with a horizontal 1" shaft. Choose this kit if you want higher cleaning performance, easy maintenance, and durable components that stand up to frequent, heavy-duty use—provided your machine's shaft orientation and connections match the pump specifications.