Where the exteriors end and the spray begins
Before any of this, agree what counts as the exterior of a feed truck. The tank shell, the rear doors and their hardware, the walkway and ladder, the chassis rails, the mud flaps and the wheel groups are the surfaces a wash plan covers. Anything behind a seal, inside a housing or carrying a printed instruction is not exterior work, even though it sits in the same line of sight and gets hit by the same stream. Naming that line out loud at the start of the job, and writing it down so the next shift sees the same version, is how a crew keeps overspray on the metal it is meant to be on.
Overspray is the part of a wash that lands where nobody aimed it. On a feed truck it matters more than on an ordinary box van, because the vehicle arrives from farms and loading bays, then drives back into the same places. Drift carries mud, tank exterior residue and whatever the last stop left behind into door hinges, lamps, mirror brackets, brake backing plates, the ladder and the underside of the tank skirt, and none of those surfaces belong to the cleaning task. The practical control is not a gentle hand on the lance: it is a physical boundary set up before water moves, an order of work that moves the dirt in one direction, and a crew that knows which parts of the vehicle are off limits.
Set the boundary before the first rinse
Decide what is being cleaned and what is being protected while it is cleaned, and mark the protected items so the crew at the lance is not relying on memory. Lamps, reflectors, camera housings, electrical connectors, air-line couplings, brake chambers, the fill hatch seal, the display unit beside the cab and any sticker or label that must stay legible all belong on the protected side. Cardboard, tape and plastic sheeting work for the flat ones; for openings the answer is simply to keep the lance away and finish the surrounding panel last. A short written exclusion list taped inside the bay is what makes the boundary survive a busy shift, and it is also what a supervisor signs off afterwards.
Work from clean to dirty and let gravity take the run-off
Order is the cheapest way to reduce spray travel there is. Start high on the tank and move down, work one side completely before crossing over, and leave the wheels, the chassis rails and the mud flaps until the end, because that is where the heaviest material sits and every pass there throws the widest fan. Keep the nozzle moving, keep it square to the panel instead of raking along a seam, and step back so the stream spreads over a wider patch rather than concentrating in one place. Standing water should always be travelling away from a surface that has just been finished, towards the part still waiting its turn. When a panel is coated with road film, a loose pre-rinse from a distance removes the bulk, and the closer, slower pass that follows needs far less force to do the same job.
Match the equipment to the standing job
Spray behaviour is a property of the machine as much as of the person holding the lance. A unit that holds its pressure while the trigger is pulled and released between passes throws far less mist than one that surges each time it restarts, and a nozzle chosen for sheeting a large flat panel behaves differently from one meant to lift caked material off a tread. The mobile truck steam cleaning equipment listed on the site is built for crews who wash vehicles in a parking yard or garage bay and move between spots during the day, with hot-water and steam modes for oily film on panels and running gear; the fixed transport truck exterior steam cleaning unit sits beside a standing wash position where the vehicle parks and the crew walks around it. Which of the two shapes the spray pattern staff have to control is a choice made at selection, not afterwards.
Make the limits of the job plain
Worth stating plainly, because it is where crews get into trouble: this kind of equipment treats the outside skin of the vehicle. It does not enter the tank, it does not clean an interior surface, and exterior work alone does not make a load compartment fit for feed. Anything inside the drum belongs to a different task with its own entry rules and its own approval. Keep the vehicle parked where the water can run to a drain rather than across the yard, keep hoses clear of the path the crew walks, and stop when a panel is wet rather than continuing to polish it. A short end-of-job check around the lamps, the mirrors, the seals and the display unit catches the drift that escaped the boundary while it is still easy to wipe off, and it is the last chance to hold down overspray before the truck leaves for a loading bay.
Where a fleet washes more than one truck body shape, the boundary, the order of work and the reach of the lance all shift with the vehicle, so the wash plan is set up for each type rather than assumed. customized steam cleaning equipment is the route the supplier takes for that case, working from the yard layout and the vehicles actually in it.
