When buying a hot-water high-pressure cleaner it is important to make sure it is a low-emission unit. Upright burners with continuous ignition are particularly effective in achieving a high degree of efficiency, as no fuel residuals can settle at the bottom, and there is less condensation. Many units can be run on environment friendly biological diesel fuel, if required. There are electrically heated HP cleaners with no emissions for special applications in wash rooms/WCs and in the pharma, food and beverage industry.
Another important aspect is the required power supply. Compact units can usually be connected to standard AC power outlets. Heavy-duty units, however, normally require a 400V, three-phase power supply. A diesel or petrol-powered unit with a water tank is the answer for total independence from water and power supplies. Most high-pressure cleaners can pick up water from external reservoirs such as ponds and water butts. An integral fine-mesh filter retains dirt particles to protect the pump from damage.
The water temperature can normally be varied between 20 and 155°C to suit the application and save energy. Many stains can be easily removed at temperatures of about 60°C. In this case modern units can be permanently set to the so-called Eco mode in order to reduce fuel consumption by up to 20%.
Brass and stainless steel for a long service life
An important criterion when choosing a new machine is its useful service life. In high-quality pumps, the cylinder head and components through which water flows are made of corrosion-proof brass. Stainless steel valves are another quality mark. High-quality pistons are also made of stainless steel or protected by ceramic sleeves or coatings.
Low-speed four-pole motors have a particularly long service life. Compared to air-cooled motors, those cooled with feed-water do not overheat even in high ambient temperatures. An electronic motor monitoring system comprising automatic shutdown, if thermal problems, dry run or sub- and overvoltage occur. In the case of overload, for example, or if the trigger gun is not activated for a certain time, the automatic shutdown protects the motor and pump unit, because water is otherwise pumped in a closed circuit which eventually leads to signs of wear.
Reinforced and abrasion-resistant hoses are particularly durable and can be subjected to heavy loads. They are mounted in an anti-twist rotary coupling in the trigger gun for easy handling. If the high-pressure cleaner has an on-board hose reel, the hose can be easily wound up so it is stored perfectly and also protected from being accidentally run over or other damage.
The trigger gun should be comfortable to hold and require minimum effort to operate. On very user-friendly trigger guns, pressure and water flow can be adjusted directly on the handle. A pivot-mounted spray lance which is angled at its front end allows the user to get into corners and other area that are difficult to reach. The bend counteracts the kickback forces to a certain extent and makes the lance easy to hold during high-pressure cleaning. It is convenient and saves time if the spray lance and nozzle can be changed without the need for tools.
The heart of the matter – nozzles
The heart of a high-pressure cleaner is the nozzle which shapes the water jet. Even a slight change in the geometry of this seemingly inconspicuous component can have a big effect. The so-called power nozzle, for example, is shaped in such a way that it produces a sharp-contoured, concentrated jet of large, coherent droplets which removes dirt much faster than a normal nozzle, using less water and detergent in the process. The reason is the higher mechanical impact pressure achieved by this nozzle – it is about 40% higher than a conventional nozzle.
Basically, the pressure impact breaks up and loosens the layer of dirt, thus producing the desired cleaning effect. The bigger, faster and more concentrated the impact of the water droplets on the surface, the better the cleaning result. The factors involved in this process are nozzle pressure, water flow rate, the geometry and spray angle of the jet. The factors depend essentially on the shape and size of the nozzle orifice. Narrowing the flow ports converts pressure into kinetic energy. The force of impact decreases as the distance between the nozzle and object being cleaned increases; at a distance of 30cm, it is only one hundredth of its initial value. Depending on type of surface and degree of soiling, the spraying distance should be no greater than 10 to 30cm.
There are three different jet patterns, i.e. fan, pencil and rotary jets. The fan jet achieves high area coverage: Water emerges from the nozzle at a spray angle of up to 45° to create a broad jet. This type of jet is also used for applying detergents and disinfectants.
The concentrated pencil jet, on the other hand, achieves a high impact pressure and very good mechanical dirt removal. Therefore heavily soiled areas are best cleaned with pencil-jet nozzles. The working width and area performance, however, are relatively small because of the narrow spray angle.
The so-called rotary nozzle combines the cleaning power of a pencil jet with the higher area coverage of a fan jet. The rotary nozzle’s pencil jet, which rotates at high speed and the linear movement of the spray lance, produces a wide spray pattern that uniformly covers the surface to be cleaned. The rotary nozzle achieves an area coverage which is ten times greater than that of conventional pencil-jet nozzles and is therefore ideally suited for heavily soiled surfaces which are insensitive to pressure.
A combination of several nozzle types is also possible. There are triple nozzles which allow the user to work alternatively with a fan or pencil jet without having to change the nozzle, and to add detergent in the low-pressure mode.
The power nozzle (right) with its special nozzle geometry achieves an impact pressure which is about 40% higher than that of a conventional nozzle.
Spray patterns of fan jet, pencil jet and rotary jet (right). The rotary nozzle combines the area coverage of a fan jet with the cleaning power of a solid pencil jet (centre).
On the whole, HP cleaning, like mechanical cleaning in general, is increasingly gaining significance in industrial operations in India. There are two reasons in particular for this. Firstly, the increasingly complicated and hence more sensitive machines need to be protected from dirt which is becoming more and more time consuming and costly and secondly, staff-intensive cleaning work needs to be streamlined. There is an array of cleaning problems that simply cannot be resolved economically without high-pressure cleaning. This applies in particular for operations where hygiene is the top priority, so in the pharmaceutical industry and the food industry, for example.
HP cleaners today are used in Indian industry for a very wide range of purposes but mainly for machine cleaning and production plant equipment cleaning as two typical fields of application.
But also in areas outside of production, for example kitchens, sanitary facilities and vehicle fleets, HP cleaners are being used for many different jobs time and again.
Kärcher Cleaning Systems Pvt Ltd