Biswing Pressure Washer Pump 1" Shaft Horizontal Triplex Plunger — 4400 PSI, 4 GPM Direct Drive

Biswing Pressure Washer Pump is a direct-drive, horizontal 1" shaft triplex plunger replacement pump rated up to 4400 PSI and 4 GPM for cold-water gas pressure washers.

This heavy-duty replacement pump is built to restore or upgrade performance on horizontal-shaft gas engines (9–15 HP / 270–340cc). It uses a triplex plunger design and a one-piece brass pump head for steady flow and improved durability, and includes an adjustable unloader valve so you can match pressure to your engine and cleaning task. The unit is supplied with common mounting hardware and accessories for quick installation on compatible models.

Which engines and pressure washers will this Biswing pump fit?

The pump is designed for horizontal 1" shaft gas engines and fits many popular makes and models used in cold-water pressure washers. It connects with a 3/4" NH garden hose inlet and a 3/8" quick-connect high-pressure outlet for wide compatibility.

• Fits 9–15 HP (270–340cc) horizontal engines only (1" shaft).
• Compatible with Honda GX270, GX340, GX390 and common Simpson, AR, General Pump, Comet, Mi-T-M models.
• Includes standard mounting bolts, shaft key, detergent hose and multiple O-rings for installation.

How do I adjust pressure and use the unloader safely?

The included adjustable unloader lets you fine-tune outlet pressure to suit cleaning tasks and engine load, improving efficiency and reducing stress on the motor. Turn the unloader valve to raise or lower working pressure; when lowered, the engine can idle for reduced noise and wear.

• Twist the unloader valve to increase or decrease pressure output.
• Lower pressure to switch the engine toward idle and reduce noise during pauses.
• Factory pressure is conservative—adjust gradually to avoid overloading springs or the engine.

What maintenance is required to keep the pump running well?

The pump uses an oil-lubricated crankcase visible through a sight glass, so you can monitor level and contamination without a dipstick. Regular oil checks and scheduled changes help protect seals and bearings; the pump ships without oil, so add the correct lubricant before first use.

• Inspect the sight glass before each run to confirm oil level and clarity.
• Add oil before initial startup—pump is shipped dry.
• Change oil roughly every 60 hours of operation or per working conditions.

What comes in the box and are there installation notes?

The pump package includes the replacement pump and commonly required hardware and fittings to simplify installation on many systems. Note that the pump is intended for cold-water use only and that pressure may need to be adjusted after installation to protect internal springs.

• Included: pump, detergent hose, vent plug, shaft key (6.3×6×54 mm), 4 bolts, 4 spring washers, 4 flat pads, 21 O-rings.
• Warning: not pre-filled with oil — add oil before first use.
• Adjust regulator pressure after installation; do not force maximum factory pressure to protect components.

Who is this for? The Biswing triplex plunger pump is aimed at mechanics, rental facilities, contractors, and homeowners who need a robust, serviceable replacement for horizontal-shaft gas pressure washers. Choose this pump if you have a compatible 1" shaft engine and want a durable brass-head design, adjustable unloader, and a kit of installation parts to get back to cleaning quickly. If your system uses a vertical shaft or hot-water operation, select a pump designed for those conditions instead.