Soft wash system setup: pump, tank and hose

Most operators start soft washing through the pressure washer: a downstream injector pulls chemical into the stream after the pump and a black soap tip drops the pressure. That draw runs about 1:8 to 1:20, so the mix is always diluted on the way out. A 1:10 draw with 12.5% stock puts roughly 1.1% on the wall, and even a strong 1:8 draw tops out near 1.4%. The downstream injector calculator runs that arithmetic for your own draw.

That covers most of the siding band, where this site works to 0.5–1.5% SH at the wall. It cannot reach the ~3% SH at the shingle a roof needs. A dedicated soft wash system solves that by skipping dilution altogether: a 12-volt pump moves the tank’s contents straight to the tip, and the pressure washer stays switched off. If you are still deciding whether soft washing is your work at all, start with what soft washing is; this page is the equipment build-out.

The heart of the rig is a small positive-displacement diaphragm pump on 12 volts DC. These are agricultural spray pumps at heart. One maker, Remco, lists its 12V lines at open-flow ratings from 3.2 to 7.0 GPM, with the configurations it lists set at 60 or 100 PSI, and names “bleach and softwash chemical spraying” as an application for its SmoothFlo pumps. Those are spray-pump numbers, nowhere near a pressure washer’s.

Read the curve before you read the box. “5.3 GPM” is open flow, with nothing pushing back. At 60 PSI of back-pressure the same pump moves 3.0 GPM and draws 16 amps; at 100 PSI it moves 1.55 GPM. Hose length, a small tip and a kinked reel all add back-pressure, so every one of them costs you flow at the gun.

• Pressure control. A demand pump stops when you release the trigger and starts when you squeeze. The maker caps rapid on/off cycling at 6 times a minute; a pump that pulses at the gun is cycling, and the fix is a tip or bypass setting, not more pressure.
• Duty cycle. These are intermittent-duty motors. Remco’s guidance is 15 minutes of cool-down for every hour of run time.
• Strainer. A 50-mesh inlet strainer, as the maker recommends, keeps tank grit out of the valves.

Hypochlorite’s safety data sheet lists it as corrosive to metals and names metals and acids as incompatible materials. Everything it touches on the rig has to be chosen for that, and the pump is only one part of it.

• Pump. The data sheet quoted above lists a polypropylene housing, Viton valves and a Santoprene diaphragm. Read the wetted materials on the data sheet of the pump you buy.
• Hose. “Chemical hose” is not one material. Buy hose whose maker rates it for sodium hypochlorite on its own chemical chart.
• Fittings and valves. Keep bare metal off the chemical side wherever you can, and flush any that cannot be avoided.

The habit that matters most is cheap: Remco says SmoothFlo pumps used for soft washing need flushing with clean water at the end of the day. Run water through pump, hose and gun before the rig is parked.

A batch rig is the simple build. You mix the tank to the strength you want on the surface and pump it out as it is. For siding that is 0.5–1.5% SH at the wall, roughly 1 part 12.5% SH to 8–12 parts water plus surfactant. For a roof it is ~3% SH at the shingle, roughly 1 part SH to 3 parts water. Always add bleach to water, never water to bleach. The soft wash mix calculator turns a tank size into exact quantities.

A proportioner keeps stock and water apart and blends them on the way to the reel. Either two pumps feed a manifold, or one pump takes a metered draw of stock, with valves or metering tips setting the share of each.

Every sizing question on a rig comes back to the pump curve. Gallons out equals real flow at your working back-pressure times trigger minutes, not the open-flow number on the box. The worked example below uses example inputs; put in your own.

• Tank. Size it to a day’s work plus a margin, then check what that weight does to your vehicle’s payload. Liquid is the heaviest thing on the rig. When the rig rides on a trailer, where that tank sits is covered in pressure washing trailer setup.
• Hose. Match it to the pump ports (Remco ships 3/4-inch quick-attach or 1/2-inch FNPT) and carry the longest run you actually walk from the truck. Extra hose is extra back-pressure, and the curve shows what that costs.
• Battery. Paper hours shrink: the motor needs its cool-down, and a battery should not be run flat. Charge it every night. Remco notes that operating pressure varies with line voltage, so a tired battery is a weak pump.
• Fuse. Remco’s rule is the next fuse size above the max amps on the pump label, on wire no lighter than the pump’s own leads.

The rinse still needs clean water. If the house spigot is weak, size a water tank with the buffer tank size calculator.

The 12.5% SDS reads plainly: causes severe skin burns and eye damage. A rig puts that liquid under pressure in a hose you walk around all day, so the protection lives on the truck, not in the van.

• Chemical goggles, which is what the SDS names for eye protection. Not safety glasses.
• Chemically resistant gloves. The SDS lists nitrile, neoprene, natural rubber and PVC among suitable materials, and says to avoid polyvinyl alcohol.
• Protective clothing, with face shield, boots or apron chosen for the task, as the SDS puts it.
• Eyewash on the rig. The SDS wants an emergency eyewash immediately available and calls for flushing skin or eyes with water for at least 15 minutes.
• Vented, shaded tank. The SDS says to store it in a vented container, away from sunlight.

For walls the injector stays a fair choice, as cleaning vinyl siding shows, and soft wash vs pressure wash covers which surfaces take which.