SIMPSON AAA 90038 Horizontal Triplex Plunger Pressure Washer Pump Kit — 3800 PSI, 3.5 GPM, 1" Shaft, Includes Hardware

The SIMPSON AAA 90038 horizontal triplex plunger pressure-washer pump kit is a direct replacement pump that delivers up to 3800 PSI at 3.5 GPM for gas-powered machines with a 1" shaft.

This heavy-duty replacement pump is built for commercial and homeowner pressure washers that require a reliable, high-pressure solution without replacing the whole unit. Designed to fit many horizontal-engine machines (for example those using a Honda GX270 style shaft), the 90038 swaps in using an SAE bolt pattern and includes the hardware and siphon tube needed for installation. The pump balances power and durability through oversized bearings, stainless-steel components, and an integrated unloader with easy-start functionality.

How hard is it to install the 90038 replacement pump?

Installation is straightforward for anyone familiar with pressure washer maintenance. The kit contains the mounting hardware and siphon tube so you can bolt the pump to machines with a matching SAE bolt pattern and a 1" shaft diameter.

• Includes mounting bolts and siphon tube for quick swap-in
• Fits horizontal-engine setups—confirm engine orientation before buying
• 1" shaft coupling required; measure your engine shaft to verify fit

What performance can I expect from this pump in typical cleaning jobs?

This triplex plunger pump produces up to 3800 PSI and 3.5 GPM, giving strong cleaning force for heavy-duty outdoor jobs while keeping engine load efficient. PowerBoost Technology increases nozzle pressure when you need more cleaning bite, and the manual adjustment lets you dial down pressure for delicate surfaces.

• Maximum 3800 PSI for tough stains on concrete and equipment
• 3.5 GPM for steady flow during prolonged cleaning runs
• Adjustable hand knob for reducing output without tools

What durability and maintenance features are included?

Built for long service life, the pump uses dual oversized ball bearings to reduce friction and wear. A stainless-steel integrated unloader and advanced oil-seal design help prevent premature failure, while a sight glass simplifies oil checks without needing a dipstick.

• Dual oversized ball bearings for extended uptime
• Stainless-steel unloader with easy-start reduces starter strain
• Sight glass lets you monitor oil level and detect contamination quickly

Which hoses and accessories work with this replacement pump?

The 90038 uses common garden-hose style inlet fittings and a quick-connect high-pressure outlet compatible with many Simpson hoses and industry-standard fittings. That makes it simple to integrate into existing setups without buying special adapters.

• Garden hose inlet for easy water supply hookup
• Quick-connect high-pressure outlet works with Simpson Armor and Monster hoses
• Compatible with many existing pressure-washer accessories and nozzles

Who this is for: The SIMPSON AAA 90038 pump kit is aimed at service technicians, rental operators, contractors, and serious homeowners who want to restore or upgrade a gas-powered horizontal-engine pressure washer. If your machine accepts a 1" shaft, supports up to 3800 PSI at 3.5 GPM, and you prefer repairing the powerhead over replacing the entire washer, this pump delivers a balance of commercial-grade durability and user-friendly features.