When there is more than one regular washing position, or when the machine's noise, heat or exhaust is a problem in the working area.

A single wash point used occasionally does not justify the pipework. Two or more regular points usually do, because the alternative is either multiple machines or moving one machine constantly.

Environment is the other trigger. Food production, laboratories, healthcare and clean areas often cannot accept a combustion machine or the noise of a pump in the room. Putting the pump set in a plant room solves it.

Hygiene arguments follow: a machine wheeled between areas carries contamination on its wheels and casing. Fixed pipework does not move.

Reliability and maintenance also improve. One machine in a clean, dry plant room with a service contract outlasts several machines living outdoors in a yard.

By the number of operators washing simultaneously, not by the number of outlets installed.

Outlets are cheap; pump capacity is not. A system with eight outlets where only two are ever used together needs a pump set sized for two, with the pipework sized to deliver to whichever two are in use.

Getting this wrong in either direction is expensive. Undersized, pressure collapses when a second operator starts and both do poor work. Oversized, the capital and the standing losses are wasted.

Ask how the site actually works: shift patterns, cleaning windows, whether wash-down is simultaneous at end of shift or spread through the day. End-of-shift cleaning concentrates demand and is what usually drives the sizing.

Variable-speed and multi-pump systems handle varying demand more efficiently than a single fixed pump running in bypass most of the day.

Adequate continuous flow, a break tank for backflow protection, and treatment where the water is hard.

The supply must sustain the system's total simultaneous demand, not its peak instantaneous draw. A supply that is marginal will cavitate pumps, which is the fastest way to destroy them.

A break tank is normally required to isolate the potable supply from the system, and it conveniently buffers a supply that cannot keep up with instantaneous demand. Tank sizing follows from that buffering role.

Water hardness matters enormously on heated systems, where scale forms in the coil and progressively destroys performance. Softening or dosing at the inlet is far cheaper than repeated descaling.

Filtration at the inlet protects pumps from grit and is standard on any permanent installation.

With falls to a collection point, an interceptor sized for the discharge, and a consent from whoever receives the effluent.

A wash bay needs the floor to fall to a channel or gully so that water does not spread across the building. That is a construction detail decided before the slab is poured, and retrofitting it is expensive.

An interceptor separates oils and solids before discharge. It has to be sized for the flow and, critically, emptied on a schedule - a full interceptor passes everything straight through and gives false confidence.

Discharge to foul sewer normally requires a trade effluent consent that may set limits on volume, pH, temperature, oil content and solids.

Closed-loop systems that treat and recirculate wash water are increasingly specified where consent is hard to obtain or water is expensive.

The requirements are jurisdiction-specific and should be established at design stage.

Yes - either with a heated pump set or by feeding the system from a central hot water plant, and the second option is often simpler.

Heated stationary systems put the burner in the plant room with proper flueing, which removes the ventilation objection that rules fuel-fired portables out of enclosed work areas.

Where a site already generates hot water at volume - many food plants do - feeding the pump set from that supply can be cheaper and simpler than a dedicated burner, provided the temperature and flow are stable and the pump is rated for hot inlet water.

Pumps have a maximum inlet temperature. Feeding hot water to a pump not rated for it destroys seals quickly, so this must be checked rather than assumed.

Insulate the distribution pipework. Heating water then losing it along a long run to the outlet is a common and expensive design mistake.

Scale control becomes essential once water is heated centrally.

Outlets positioned so a standard hose length reaches everything, with reels to keep the hose off the floor.

The design question is coverage: place outlets so that every surface needing washing is within reach of the hose length chosen, with overlap. Too few outlets means very long hoses, which lose pressure, get damaged and become trip hazards.

Retracting or manual reels at each outlet keep hoses stored, drained and out of the traffic route. In food and healthcare areas hose left on the floor is a hygiene finding.

Quick-release couplings let lances, foam applicators and brushes be swapped without tools, and standardising the coupling across the site means any accessory works at any outlet.

Isolation valves at each outlet allow one to be serviced without shutting the system down.

Where chemical is applied, decide whether it is dosed centrally or at the lance - central dosing is more consistent, lance dosing more flexible.

Scheduled pump servicing, interceptor emptying, descaling on heated systems and periodic inspection of the high-pressure pipework and hoses.

The pump set follows a normal service regime - oil, seals, valves - and being in a plant room makes that easier rather than harder. A service contract is usual because the whole site depends on one machine.

Hoses and couplings are the wear items and the safety-critical ones. High-pressure hose degrades with age, kinking and abrasion, and should be inspected on a schedule and replaced rather than repaired.

Interceptors need emptying by a licensed contractor at an interval set by use, and the records usually have to be retained for the regulator.

Heated systems need coil descaling and burner servicing as any hot machine does.

Because a fixed system is a single point of failure for the whole site's cleaning, spares holding for the common wear parts is worth planning.