Home AAA Pressure Washer Pump Guide
Pump-manufacturer compatibility
AAA Pressure Washer Pump Guide
AAA replacement-pump kits documented by SIMPSON span distinct 3/4-inch and 1-inch horizontal-shaft classes. Use the exact kit number, output, engine capacity and port orientation before treating a replacement as compatible.
AAA kit number identifies a specific pump class
Start with the existing pump or pressure-washer model, then confirm whether the engine is a 3/4-inch or 1-inch horizontal-shaft class.
For SIMPSON machines, cross-check the SIMPSON parts page before using a generic replacement path.
Last technical review for this page: August 28, 2026.
AAA pump kits now form a clear two-shaft replacement ladder
SIMPSON's current pump catalog makes it possible to separate AAA replacement classes without guessing. The 90036/90037 group uses a 3/4-inch horizontal shaft, while the 90038/90039/90034 group uses a 1-inch horizontal shaft.
| AAA kit | Published output | Shaft class | Manufacturer example / note |
|---|---|---|---|
| 90036 | 3200 PSI / 2.8 GPM | 3/4-in horizontal | Honda GX200 example; integrated unloader/easy-start; M22 outlet. |
| 90037 | 3700 PSI / 2.5 GPM | 3/4-in horizontal | Honda GX200 example; manufacturer still requires orientation check. |
| 90038 | 3800 PSI / 3.5 GPM | 1-in horizontal | Honda GX270 example; direct-drive triplex class. |
| 90039 | 4000 PSI / 3.5 GPM | 1-in horizontal | Honda GX270 example; current high-commercial replacement class. |
| 90034 | 4400 PSI / 4.0 GPM | 1-in horizontal | Honda GX390 example; highest-output class in this comparison. |
“Fits most” still does not mean verified for your pressure washer
SIMPSON describes these kits as using SAE-standard mounting patterns and standard connections, but the product pages repeatedly tell users to check pressure-washer inlet/outlet orientation. PressureWasherMatch.com keeps the result CONDITIONAL until shaft length/keying, mounting, engine power, RPM, port orientation, unloader configuration and frame clearance also match.
If the complete machine is SIMPSON-branded, also use the SIMPSON parts guide. If it is identified by Honda engine family, use the Honda-powered guide.
Do not “upgrade” from 90039 to 90034 by PSI alone
Moving from 3.5 GPM / 4000 PSI to 4.0 GPM / 4400 PSI increases hydraulic load and may exceed the engine, hose, gun, nozzle or other system limits. The higher-rated pump is not automatically a better replacement.
Use PSI vs GPM and the Nozzle Calculator only after the machine's safe operating envelope is established.
AAA 90039 options only after the 1-inch / 3.5-GPM class matches
The current 90039 specification is well documented, but it remains a conditional replacement until the machine's physical and engine-side requirements are verified.
Manufacturer sources
- SIMPSON — current pump catalog — Current AAA and OEM replacement-pump lineup.
- SIMPSON — AAA 90036 — 3200 PSI / 2.8 GPM / 3/4-in horizontal replacement class.
- SIMPSON — AAA 90037 — 3700 PSI / 2.5 GPM / 3/4-in horizontal replacement class.
- SIMPSON — AAA 90038 — 3800 PSI / 3.5 GPM / 1-in horizontal replacement class.
- SIMPSON — AAA 90039 — 4000 PSI / 3.5 GPM / 1-in horizontal replacement class.
- SIMPSON — AAA 90034 — 4400 PSI / 4.0 GPM / 1-in horizontal replacement class.
Sources reviewed August 28, 2026. PressureWasherMatch.com is independent and is not affiliated with or endorsed by the manufacturers referenced above.
Frequently asked questions
Who makes AAA pressure washer pumps?
AAA-branded pressure washer pumps are currently sold and documented by SIMPSON / FNA Group. SIMPSON publishes current replacement pump kits, specifications, manuals and warranty information.
What AAA pump fits a 3/4-inch horizontal shaft?
Current AAA 90036 and 90037 are 3/4-inch horizontal-shaft replacement classes. 90036 is 3200 PSI / 2.8 GPM; 90037 is 3700 PSI / 2.5 GPM.
What AAA pump fits a 1-inch horizontal shaft?
Current AAA 90038, 90039 and 90034 are 1-inch horizontal-shaft classes at progressively higher output: 3800/3.5, 4000/3.5 and 4400/4.0 respectively.
Is AAA 90039 a universal 4000 PSI replacement pump?
No. SIMPSON explicitly requires users to check inlet/outlet orientation, and final fit still depends on shaft, mount, engine capacity, plumbing and frame clearance.
What is the difference between AAA 90039 and 90034?
Both use a 1-inch horizontal-shaft replacement architecture, but 90039 is 4000 PSI / 3.5 GPM while 90034 is 4400 PSI / 4.0 GPM and is associated with a larger engine class such as Honda GX390.
Does this page duplicate the SIMPSON parts page?
No. The SIMPSON parts page is machine-brand parts intent. This page organizes AAA pump families themselves and links back to SIMPSON machines only where that context helps replacement selection.