Most people shopping for a pump build ask for pressure. Then they buy a surface cleaner, and discover that pressure is not what makes a surface cleaner work. Flow is. A 20 in cleaner at 3 GPM crawls; at 4 GPM it walks.

The RSV4G36-PKG is not in the current AR package lineup. The two closest packages are the RSV33G36-PKG at 3.3 GPM and 3,600 PSI, and the RSV4G40-PKG at 4.0 GPM and 4,000 PSI. The RSV4G40-PKG is the high-flow end of the range: 1 in hollow shaft, boxed with the parts you need to bolt it to an engine.

The RSV package range

All run at 3,400 RPM on a hollow shaft. The package ships as a complete boxed kit with manual, regulator, fittings, bolts and chemical hose.

Sizing an engine for the RSV4G36-PKG

EBHP is GPM times PSI divided by 1,460, and the RSV4G40-PKG needs 11.0 at the pump shaft. Small-engine horsepower is rated under favourable conditions, so add real margin: a 420cc engine in the 13 to 15 HP class is the right pairing, whether that is a Predator 420 or a Honda GX390.

Do not try to run this pump on a 301cc engine. It will start, it will make pressure with the trigger closed, and it will sag the moment you open a nozzle.

The shaft has to be 1 in hollow. Measure it rather than going by engine displacement, which does not reliably predict shaft size.

Why flow is the spec that matters

Pressure removes what is bonded to the surface. Flow carries it away and covers ground. Most jobs are limited by the second one.

• Surface cleaners. A 20 in rotary needs roughly 4 GPM to spin at working speed. Below that it turns slowly and you go over everything twice.
• Rinsing. Soap removal from a truck or a wall is entirely a volume problem. More PSI does not help.
• Long hose runs. Flow is what maintains pressure at the end of 100 ft of hose.

The catch is water supply. A domestic hose bib gives roughly 4 to 6 GPM on a good day, less through a long hose. At 4 GPM you are near the ceiling of what a garden hose can feed, so check your supply before you go higher: time how long it takes to fill a five gallon bucket.

Building a machine around the RSV4G36-PKG

1. Confirm the shaft is 1 in hollow and the engine is 13 HP or more.
2. Mount the pump to the crankshaft with the flange hardware. Get it square.
3. Plumb it: garden hose or tank feed to the inlet, high pressure hose to the outlet, detergent line to the injector.
4. Fit an inlet filter. At 4 GPM the pump is drawing hard and an unfiltered inlet is the fastest route to a rebuild.
5. Fill with non-detergent pump oil before the first start.
6. Set the regulator with the trigger open, then confirm bypass with it closed.

Where the RSV4G36-PKG fits

Contractor work: driveways, sidewalks, patios and pool decks with a 20 to 24 in surface cleaner; fleet washing for trucks, buses and vans; construction and farm equipment; apartment and HOA property maintenance.

Residential: siding, brick, stucco, fences, furniture, vehicles, RVs and boats. At 4,000 PSI, be deliberate around painted wood and old mortar. This pump is capable of doing damage a 2,700 PSI machine cannot.

Rental fleets: the rebuildable triplex design is the reason this is worth buying over a consumer unit, because rental machines get abused and then need to be repaired rather than replaced.

Keeping the RSV4G36-PKG working

Forged brass manifold, stainless plungers, oversized bearings, and replaceable valves, seals and pistons. Change the oil at 50 hours and then every 300, flush after detergent, keep the inlet filter clean, and run pump saver before any freeze.

Unsure which package matches your engine? Send the engine size and shaft diameter and you will get a specific package back.