SIMPSON AAA Triplex Pump Kit 90038
3,800 PSI · 3.5 GPM · 1 in shaft.
The SIMPSON 90038 is a replacement AAA triplex plunger pump kit rated 3,800 PSI at 3.5 GPM, for engines with a 1 in horizontal shaft. It has a garden-hose inlet and a quick connect outlet, and fits engines such as the Honda GX270.
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Specifications at a glance
| Brand | SIMPSON |
|---|---|
| Part number | 90038 |
| Pump | AAA triplex plunger |
| Engine shaft orientation | horizontal |
| Shaft diameter | 1 in |
| Max pressure | 3,800 PSI |
| Max flow | 3.5 GPM |
| Inlet | Garden hose |
| High-pressure outlet | quick connect |
| Manifold | brass |
| Unloader | integrated and adjustable, with Easy Start |
| Warranty | 5-year |
From SIMPSON's pump catalog. Anything SIMPSON doesn't state is marked as not stated.
What to know about the 90038
Shaft and orientation
The pump slides onto the engine crankshaft, so the shaft must be 1 in and horizontal. SIMPSON names the Honda GX270 as 1 in shaft engines.
Match the rating
SIMPSON's guidance is to match engine orientation, PSI, GPM, shaft diameter and the inlet and outlet connections of your current pump. This kit is rated 3,800 PSI at 3.5 GPM; after any pump change, size your nozzles to the new rating with the nozzle size calculator.
Key features (from SIMPSON)
- AAA triplex plunger pump
- 3,800 PSI at 3.5 GPM
- 1 in shaft, horizontal engines
- Brass manifold
- Unloader: integrated and adjustable, with Easy Start
- Garden-hose inlet, quick connect outlet
- 5-year warranty
Is it right for you?
| Good choice if | your engine has a 1 in horizontal shaft and your washer was rated close to 3,800 PSI at 3.5 GPM |
|---|---|
| Look elsewhere if | your engine shaft is not 1 in |
| Look elsewhere if | your engine is vertical-shaft |
| Look elsewhere if | your hose uses M22 threads and you don't want adapters |
Questions about the 90038
Will the SIMPSON 90038 fit my pressure washer?
It fits engines with a 1 in horizontal shaft and the standard SAE bolt pattern, on washers rated around 3,800 PSI at 3.5 GPM. Check your engine shaft and your current pump's inlet and outlet first.
Do I need new nozzles after changing the pump?
Only if the new pump's rating differs from the old one. Work out the right size for 3,800 PSI at 3.5 GPM with the nozzle size calculator.
Does the 90038 need oil?
Triplex pumps have an oil crankcase. See pump oil capacity by pump and follow the manual for your kit.
What to check before buying
Other 1 in shaft pump kits
- SIMPSON 90039 4,000 PSI · 3.5 GPM · AAA Triplex
- SIMPSON 90034 4,400 PSI · 4.0 GPM · AAA Triplex
Source and editorial status
Manufacturer reference: SIMPSON pump catalog ↗ and SIMPSON product page ↗. Specifications checked 3 November 2026. We have not tested this product.