Start from the faces, not from the machine
A hydraulic assembly is not one surface. Around a single power unit you will find the reservoir shell and its lid, the pump and motor bodies, the manifold and valve block, the filter heads, the gauge and sight-glass faces, the piping and the clamps that hold it, the cooler with its finned face and fan guard, the electrical enclosure, and the printed plates that tell people which line this is. Each of those holds a different kind of soil, and each reacts differently to heat and moisture.
Split them into three columns before any equipment conversation. Faces where the film is fresh and the surface is open metal or painted steel. Faces where the deposit has been cooked on by the heat of the machine and has gone hard at the corners of the valve block and around the pump mounting. And faces that should not be worked on at all in this round. The third column is the one that decides whether the exercise is safe, and it has to be written down by the people who own the equipment, not inferred from a brochure.
Why the mobile part is the point
Most hydraulic assemblies never move. They are bolted to a machine frame or to a trolley inside a bay, and removing one for cleaning would take the line out of service. That rules out any method that depends on carrying the workpiece to a fixed wash station. A unit that can be walked or driven to the position, set down, and connected to what the bay already offers is the only version of steam cleaning that reaches this class of equipment at all.
It also changes the economics of the round. A fixed installation earns its keep by volume; a portable unit earns its keep by being able to stand next to a different machine each time. If the plant has a handful of hydraulic assemblies spread across several bays, the portable arrangement is usually the only one that covers all of them. If there is one machine, cleaned on a fixed cadence, at a fixed spot with a fixed utility available, a stationary installation becomes worth comparing instead.
What has to be true at the position
A portable unit is portable up to the limit of what it needs from the floor around it. Walk the route with a tape measure and a torch before agreeing anything with a supplier.
- A route the unit can actually travel: aisle width, door width, the height of anything overhead, the threshold or ramp it has to cross, and what is underfoot on the way.
- A standing position for the operator that is stable, level, and does not require reaching across a live machine to hold the wand.
- Electrical supply at the position, on the correct circuit, with the device the site allows interrupting the supply, and with the cable routed where no one will trip over it or park a truck on it.
- Water for the tank, and an honest idea of how far away it is, because refill walking is real time and it shows up in the cost of the job.
- Somewhere for the run-off to go. Degreased water coming off a hydraulic assembly is a waste stream, not a puddle, and the plant has to decide in advance where it is collected and how it leaves the site.
- The time window: who signs the equipment off for cleaning, who isolates what, and who signs it back.
Where a portable unit and a fixed one divide
The dividing question is not which is more powerful. It is where the constraints sit. A machine that carries its own working supply can work in a bay with no plumbing, but its working session has an end, and the round has to finish inside that session or be planned as two rounds with a change of supply in between. A machine fed from the site usually runs longer, but the round is then bounded by cable reach, and the survey becomes a map of sockets rather than a map of machines.
For hydraulic work this matters more than it does on a vehicle, because the assembly rarely sits near a service point. Vehicle cleaning is what this mobile steam cleaning machine category is written around, and it is worth being straight about that: the published descriptions talk about garages and tight parking, not about power packs. The plant is proposing a duty the catalogue does not describe. That is not a reason to stop, but it is a reason to make the supplier answer for the actual duty instead of assuming the category page covers it.
The exclusion list comes before the cleaning plan
On a hydraulic assembly the items to keep out of the round are usually the same handful everywhere: gauge faces and sight glasses, the electrical enclosure and every cable gland and connector that enters it, breathing vents and the filler path into the reservoir, shaft seals and rod wipers at the ends of cylinders, gaskets, labels and plates that carry information, and any joint that is already showing a weep.
A seal that is holding because it is dry is a seal that may not hold once it has been heated and washed. Write each excluded item on the job sheet with the reason and with the hand-clean method that replaces the machine on that face. An exclusion with no fallback is not an exclusion; it is a gap in the record that nobody agreed to.
Decide the mode from the deposit
These machines are generally presented with more than one working mode, typically a drier steam, a wetter steam, and a hot-water stage. Which one is right is a property of the soil and the surface, not a default.
A fresh oily film on an open face responds quickly and needs as little free water as possible, because the water is what has to be contained and chases its own path downhill. A baked, darkened skin at a hot corner needs heat and time to soften, and one pass over it tells you nothing. A final rinse stage may be wanted where the surface has to be visibly clean for an inspection, or may be unwanted exactly because of the water it puts on the assembly. Choose per face, write the choice on the sheet, and expect the same face to need a different choice the first time it is done compared with the maintenance rounds that follow.
Where the deposit is heavy and long-established, the round is a removing-the-film task first and a finishing task second, and it is worth saying so in the enquiry: heavy grease removal equipment is how the range is indexed for soil of that kind, and the supplier should be asked to state which mode is meant to do the work.
Prove it on a taped patch, not on the whole assembly
Pick two or three small areas that carry the worst of the film, mark them, and photograph them before anything happens. Work one patch with the chosen mode, then stop. Judge it only once it is dry and cool, and have the judgement made by someone who was not holding the wand. Compare the photographs.
Inspect the ground around the patch as carefully as the patch itself: behind the flange, under the clamp, at the seam where the enclosure meets its lid, along the run-off path to wherever the water went. That is where a failed attempt shows up, and it shows up later than the cleaning does. Write down, for each patch, which mode was used, how long it was held, what came off, what did not, and what appeared at the edges. The trial that proves nothing is the one where the operator remembers what they did and nothing was recorded.
Define the end state in conditions you can see. Say what a finished round means on this equipment in terms someone can verify without a laboratory. Typical conditions: the dial and sight window can be read from the normal standing position at the normal distance; the identification plates can be read; no film remains on the faces agreed for this round; no fresh wet is sitting at a joint, a seal or a fitting after the assembly has been given time to dry; nothing that was working before the round has stopped working afterwards.
That last condition is the one that decides whether the method is allowed into the plant at all, and it is the reason the exclusion list and the taped patch exist.
What a clean round has to leave behind
A round that fits is a round someone can run again without re-deciding everything. That means a job sheet per assembly carrying the surface list, the exclusions with their fallbacks, the mode chosen for each face, the standing position, the utility and run-off arrangement, and the conditions that count as finished. It means the round is timed against the production window it is allowed to occupy, and it means knowing how far the operator has to walk for water and how many times that happens in a session.
Interval is a decision about how fast the film comes back, not about the calendar. A face beside a process that throws oil will need a shorter gap than an idle face across the aisle, and cleaning ahead of a scheduled inspection is usually worth more than cleaning on a date.
Fitting the machine into the bay
Once the faces, the position and the exclusions are written down, the equipment question gets short and answerable. What the plant needs is a unit that can be brought to this bay, stood on this floor, connected to this supply, and run through this list inside this window, and that duty is a different enquiry from the one a wash bay would send.
Where the soil is heavy and long-established, the round is a removing-the-film task first and a finishing task second, and the enquiry should say so plainly rather than call it a wash. The supplier should be asked which mode is meant to break that film down, and how many passes at that face the answer assumes.
Write the questions the same way to every supplier and the answers separate quickly. Which published page states the figures for the exact unit being quoted, and which figures are not published at all? Has a unit of this type been worked on a reservoir, a manifold or a cylinder housing, and what evidence exists from that job? Which mode is meant for baked-on oil at a hot corner, and which faces of such an assembly would your own operator refuse to work on? How long does one working session last at this position, and what ends it? What does the unit need from the site, and how far may the operator be from each of those things? If the plant later needs a different arrangement for the same family of machines, what changes and what has to be re-confirmed? The site enquiry route for customized steam cleaning equipment is where that conversation starts.
Where it stops fitting
The arrangement stops being sensible when the exclusion list removes most of the value: if the film sits mainly behind flanges, under clamps and inside finned cooler faces that no wand should be pointed at, a surface round will not reach it and no amount of equipment will change that. It also stops being sensible when the plant cannot isolate the equipment, cannot decide where the run-off goes, or cannot give a window long enough to work slowly.
Those are not reasons to abandon the idea. They are the conditions to write into the enquiry. Say what the round is meant to achieve, say what is out of scope, and ask the supplier to mark the sentences they cannot support rather than nodding at the whole document. A mobile unit that is fitted around these constraints is a useful thing to have standing in the bay. One that is bought against a category page which never described this duty is an expensive object to argue about later.
