Beating dirt with High-pressure Washers

In the automotive sector they enable effective cleaning of engines, chassis and small parts as well as vehicle surfaces. You usually find pressure washers, especially the stationary type, where hygiene is of prime importance – in swimming baths, hospitals or businesses where foodstuffs and drinks are produced or stored. You also find them cleaning building facades or used in private homes and gardens.

Generally, the aim of cleaning is to apply an appropriate method to move from a specific starting situation to the desired (cleaning) goal. The starting situation is determined by the type of soiling, which may consist among other things of salts, dust, sand, oil, urine scale, protein or germs. Depending on the method chosen, four cleaning objectives can be reached, as follows:

  • Optical cleanliness (no dirt visible to the eye)
  • Physical cleanliness (no soiling can be identified, even with a magnifying glass or microscope)
  • Chemical cleanliness (free from oxide residues or residual chemical films)
  • Bacteriological cleanliness (free from living micro-organisms).

Contact pressure greatly influences cleaning outcome

It is not so much the contact power as the contact pressure, i.e. the pressure with which the jet of water impacts on the surface to be cleaned and dislodges a dirt particle. Contact pressure depends on spraying distance, angle of spray, nozzle pressure and water flow rate. The nozzle pressure is determined by the water flow rate and the nozzle diameter. The same applies to pump pressure, though this has in addition to compensate for line resistance.

The range of uses and outputs, especially of hot-water pressure washers, is impressive. This is because in addition to the dirt-dissolving properties of water, pressure and detergent, the possibility of using varied temperatures is a contributing factor. For example, you can dissolve substances such as grease, oil and similar soiling better and faster with hot water.

The steam setting (boiler temperature up to 140°C) is good for gentle cleaning of especially pressure-sensitive surfaces, since dirt that could otherwise be dislodged only by high pressure can be removed with hardly any pressure at all at extremely high temperatures. That is why the steam setting is also suitable for cleaning porous natural materials that absorb water easily.

With cold-water pressure washers, it is necessary to compensate for the insignificance of the temperature factor by increasing contact pressure, detergent use and time spent. However, cold-water pressure washers can be used with hot water up to 60°C.

If the temperature, as one cleaning factor in a hot-water pressure washer, is increased from c. 12°C to 80°C, the other factors – mechanics (= contact pressure), time and detergent – can be decreased. If the water temperature is raised to 80°C, the cleaning factor temperature results in

  • a similar cleaning result at lower contact pressure
  • a better cleaning result at the same contact pressure
  • better softening of greasy dirt and
  • a shorter cleaning time.

A final word on this subject: by using hot-water pressure washers, which in any case produce a better cleaning result, one can considerably reduce working times compared with cold-water machines. This in turn leads to faster amortisation.

Pressure washer accessories increase range of uses

Suitable accessories used in combination with a pressure washer are a great help to those with special cleaning requirements. Moreover, they save labour and time.

Modern hard surface cleaner makes rinsing unnecessary

One example is the modern hard surface cleaner. It is especially good for cleaning structured surfaces such as non-slip tiles in canteen kitchens. A rotating nozzle beam that is set in motion by the thrust of power nozzles rinses dirt from large surface areas without damaging grout or joints. An all-round splashguard prevents dirty water splashes so there is no need to rinse and dry walls or fittings after cleaning. A hard surface cleaner with an integrated Venturi nozzle has proven especially effective for this kind of cleaning. The negative pressure generated by the Venturi nozzle causes the dirty cleaning fluid to be carried along by part of the high-pressure water and channelled via a separate wastewater hose to where it can drain off safely. With conventional hard surface cleaners, you have to rinse and vacuum or wipe the cleaned surface because the dirty water stays around. A hard surface cleaner with an integrated suction device obviates the need for this operation.

The gutter cleaner is for cleaning gutter drainage systems, which can be done without removing the grille. This saves the user a great deal of time because dismantling covers that are screwed firmly into place is often very time-consuming. A spray lance at least 50cm in length must be mounted between hand-held spray gun and cleaner, otherwise there is a risk of recoil. The water flow rate should not exceed 1,200 l/h. That will drive the dirt from the gutter into the drainpipe without any problems. But be careful: the hand-held spray gun should only be operated when the gutter cleaner has been pushed through the cover grille to support it.

Pipe cleaning kits shift even stubborn deposits

Another cleaning task that keeps cropping up is cleaning heavy-duty drainpipes that have become blocked or clogged. Pipe cleaning kits have proven very effective for this. They shift even stubborn deposits on the inside walls of pipes and wash them out through the pipe with a reverse water flow.

The openings in the pipe-cleaning nozzle point backwards, so the nozzle and the especially flexible hose penetrate the pipe to be cleaned under their own momentum. There is no need to push unless the pipe is very long or curved. To prevent accidents, once it has entered the pipe the pipe-cleaning hose must never be withdrawn while under high pressure.

A telescopic lance is the right choice for cleaning hard-to-access high places that cannot be reached with the pressure washer’s standard accessories. The telescopic lance is infinitely extendable from 1.80 to 5.40 metres. The high-pressure hose runs inside the lance. Rotating couplings prevent twisting.

For fast application of any detergent in foam form, it is advisable to use the short, handy cup foam lance, with which the detergent is dosed by turning a knob on the lance itself. It is important to ensure that the foam is applied top-down to avoid large piles of it from accumulating. If they do, the weight of the foam will make it slide off the surface too quickly without having time to take effect. After the foam has taken effect, the surface should be rinsed with drinking-quality water.

Quick coupling systems speed up accessory changes

Quick coupling systems can speed up the change from one spray lance or accessory to another considerably. The coupling is screwed firmly to the hand-held spray gun. In addition, all accessories that can be changed are fitted with a plug nipple. Like that, changing accessories is a matter of seconds.

Finally, a few practical tips:

  • Food sector operators should only use high-pressure hoses with a non-marking cladding that are resistant, if need be, to animal fats (grey or blue colour).
  • Pressure washer operatives must wear personal protective gear to protect their bodies. As a rule, waterproof trousers and jackets to protect against wet, rubber boots and gloves will suffice.
  • A splashguard must be used if a rebound effect from dislodged surface parts is likely. It is advisable to wear goggles to protect the face, or a see-through helmet visor.
  • The flow of liquid must never be directed at anyone’s body, including the operative’s own. It is also important to ensure that there is nobody in the immediate vicinity while cleaning is under way.
  • All live electrical parts in the area of cleaning work must be protected against water jets. And plugs must not be touched with wet hands.
  • Hosepipes should be run so that they cannot be damaged or get caught up or run over. And each time hosepipes are taken into operation they should first be checked visually for damage. Defect pipes must be reported and exchanged.
GerdHeidrich
Kärcher Training Manager, Niels W. Buhrke, freelance journalist

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