SIMPSON AAA Triplex Pump Kit 90037
3,700 PSI · 2.5 GPM · 3/4 in shaft.
The SIMPSON 90037 is a replacement AAA triplex plunger pump kit rated 3,700 PSI at 2.5 GPM, for engines with a 3/4 in horizontal shaft. It has a garden-hose inlet and a threaded M22 outlet, and fits engines such as the Honda GC190 and GX200.
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Specifications at a glance
| Brand | SIMPSON |
|---|---|
| Part number | 90037 |
| Pump | AAA triplex plunger |
| Engine shaft orientation | horizontal |
| Shaft diameter | 3/4 in |
| Max pressure | 3,700 PSI |
| Max flow | 2.5 GPM |
| Inlet | Garden hose |
| High-pressure outlet | threaded M22 |
| 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 90037
Shaft and orientation
The pump slides onto the engine crankshaft, so the shaft must be 3/4 in and horizontal. SIMPSON names the Honda GC190 and GX200 as 3/4 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 3,700 PSI at 2.5 GPM; after any pump change, size your nozzles to the new rating with the nozzle size calculator.
Outlet and hose
The outlet is threaded M22, so it takes the M22 hoses most homeowner gas washers use, such as MorFlex.
Key features (from SIMPSON)
- AAA triplex plunger pump
- 3,700 PSI at 2.5 GPM
- 3/4 in shaft, horizontal engines
- Brass manifold
- Unloader: integrated and adjustable, with Easy Start
- Garden-hose inlet, threaded M22 outlet
- 5-year warranty
Is it right for you?
| Good choice if | your engine has a 3/4 in horizontal shaft and your washer was rated close to 3,700 PSI at 2.5 GPM |
|---|---|
| Look elsewhere if | your engine shaft is not 3/4 in |
| Look elsewhere if | your engine is vertical-shaft |
| Look elsewhere if | your hose uses quick-connect fittings and you don't want adapters |
Questions about the 90037
Will the SIMPSON 90037 fit my pressure washer?
It fits engines with a 3/4 in horizontal shaft and the standard SAE bolt pattern, on washers rated around 3,700 PSI at 2.5 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 3,700 PSI at 2.5 GPM with the nozzle size calculator.
Does the 90037 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 3/4 in shaft pump kits
- SIMPSON 90036 3,200 PSI · 2.8 GPM · AAA Triplex
- SIMPSON 90029 3,300 PSI · 2.4 GPM · OEM Technologies Axial Cam
- SIMPSON 90052 3,500 PSI · 2.5 GPM · AAA AX300 Axial Cam
Source and editorial status
Manufacturer reference: SIMPSON pump catalog ↗. Specifications checked 3 November 2026. We have not tested this product.