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Pressure cleaning of structures

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Pressure cleaning of structures

Renovation of neglected buildings has become the main activity for many companies.
Since professional preparation of the substrate is the basis for a successful renovation, every builder should be familiar with the wide range of pressure units and the highest pressure units.

In many areas, such as repairing facades or renovating concrete structures, success depends on expertly performed work related to the preparation of the substrate. The use of modern water-air-based jet technology plays an important role here.

The offer of modern devices for removing dirt from the facade using water pressure covers a wide range of pressure units: from those with a capacity of 100 bar to units with the highest pressure up to 3000 bar.

Professional 100 bar pressure units powered by two-phase current are available at an affordable price of PLN 4,000. In another price range, there are devices that generate pressure between 200 and 500 bar. For about PLN 12,000 you can buy a professional 200 bar generator with accessories.

Cleaning power is determined by many interrelated factors besides pressure; the amount of water, the construction of the nozzle and only then the water temperature.

The basic rule that applies here is: the higher the pressure and more water a waterjet can produce, the more surface area it can clean. If a 100 bar chiller has a daily capacity of 100-200 m 2 , then a 500 bar chiller can clean 800-1000 m 2 in one day.

The data expressed in bars alone does not say much – they basically only inform about the pressure in the hose. The main question, however, is the following: the maximum pressure that actually acts on the treated surface. The key issue here is the construction of the nozzle. The spot jet is much stronger than that produced by a flat nozzle. The spot jet can only be used to clean small areas, flat areas, larger ones. In many cases, a better solution is a combination of the flat jet and the impingement force of a rotary nozzle, which produces a spherical jet as a quasi-rotational spot jet.

Correct nozzle selection can therefore increase the power of the water jet. In many cases, the components are compatible: a manufacturer’s X nozzle can be used with a Y’s chiller. So you should not always buy a more powerful chiller if you expect greater performance. You can increase the performance of your machine by purchasing better accessories.

In addition to the construction of the nozzle, the hose length also has a significant impact on the power of the water jet. Currently, hoses with a length of 30 to 90 m are usually used. However, the maximum usable length of the hose, which allows to achieve a satisfactory pressure at the nozzle outlet, depends less on the length and more on the diameter of the hose. There is much greater frictional loss in thin hoses. The thinner the hose, the lower the pressure at the outlet of the nozzle will be. This is illustrated in the table below.

Pressure losses due to hose distance and diameter
performance hose length in m hoses diameter
6 mm 8 mm 10 mm
10 l/min. 600 l/h straty w ciśnieniu (bary)
10 5.8 1.5 0.5
20 11.6 3 1
30 17.4 4.5 1.5
60 34.8 9 3
120 69.6 18 6
150 87 22.5 7.5
15 l/min. 900 l/h 10 12 3.2 1.1
20 24 6.4 2.2
30 36 9.6 3.3
60 72 19.2 6.6
120 144 38.4 13.2
150 180 48 14.2
22 l/min. 1300 l/h 10 23 6 2.1
20 46 12 4.2
30 69 18 6.3
60 138 36 12.6
120 276 72 25.2
150 345 90 31.5
28 l/min. 1700 l/h 10 40 10 3.5
20 80 20 7
30 120 30 10.5
60 240 60 21
120 480 120 42
150 600 150 52.5

Also, if a machine is operated at higher pressure, and hence throws out more water per minute, that does not necessarily mean more water consumption. High efficiency means that the actual water consumption can even drop.

Temperature has the least influence on performance, but here too, the principle that nothing can be done without pressure applies. A heated stream is of little use if it is only ejected at 60 bar. The temperature should actually be applied to the nozzle. The water in the heating device has 80 o C, but it cools down considerably as it passes through the hose. The state of the water leaving the nozzle is decisive for the temperature, as in the case of pressure.

General purpose appliances offer many options.

Among the multitude of devices and methods offered, which, in combination with accessories, offer various possibilities, there is also a certain danger: too narrow specialization of the company resulting from the possession of a specific aggregate. At the outset, therefore, it is preferable to opt for an expandable general-purpose device that can be adapted to different circumstances if necessary. What options characterize such an aggregate?

  • It should be able to clean with both cold and hot water. Manufacturers usually offer equipment intended only for cold or only hot cleaning. However, there are plug-in heating modules that can be retrofitted with a cold water chiller.
  • Devices up to 100 bar are mainly powered by two-phase voltage. Only a few with a capacity of 200 bar have a similar power supply. However, they achieve comparatively low efficiency. From 200 bar, a mains connection is always required, but this is precisely what, for example, during renovation work on old buildings, in many cases cannot be found. Machines of this power should be equipped with a gasoline engine.
  • The scope of application of such a device is significantly broadened if it can also be used to perform wet sandblasting using a mixing head.

General purpose machines (internal combustion engine) are especially useful on construction sites, as they will not be excluded from traffic due to power outages typical of many construction sites. In addition, this hardware configuration allows for testing on reference surfaces to select the optimal cleaning method in a given situation.

As the effects of renovation depend on the correct preparation of the substrate, the worker must be well trained in this matter. He needs to know how the pressure aggregate works, how it is operated and what cleaning method is optimal for the given situation. For the owner of the company, this also means that the cleaning of the facade is not settled in the form of a lump sum (usually too low), but is considered to be specialized services of the company and bills, like other services, differently.

At this point, we should describe the cost-effective rates of substrate preparation per square meter depending on the surface preparation method used.
In our country, however, it is pointless because, according to our many years of experience, the rate is determined by two basic parameters:

  • contractor-investor relationship
  • lowest bid.

Method overview

& nbsp; Pressure cleaning is a rational method with satisfactory performance and due to investment costs in the range of PLN 4,000 – PLN 12,000 for one device with accessories also affordable. It is most often used for works related to the cleaning of the facade. So you can clean plastered, clinker, granite, metal or glass facades. The surface is usually treated with cold water – possibly with the addition of a cleaning agent – at a pressure of approx. 100 bar. Such works are performed with typical cold water devices with a capacity of 80 – 200 bar.

Only about 10% of hot water is used. When heated to o C or more, it is effective on a small number of surfaces, e.g. oily, greasy or sooty in heavily frequented streets.

Water blast cleaning with cold water or hot water & nbsp; (sometimes also with sand-water mixture) at a pressure of approximately 500 bar.

Beginner equipment is a 500 bar cold water chiller that removes well-adhered coatings on a tough substrate, eg when dispersion is to be replaced by mineral paint. Devices with a power of 500 bar work with a consumption of 900 to 1700 liters of water per hour. However, due to the high efficiency, the actual water consumption is not high.

The method is also used – for example at a pressure of 500 bar and the use of a rotary nozzle – for dust-free removal of plaster, whereby the joint mortar is also torn off. Since this method of plaster removal (unlike hammering and chisel) is not burdensome for the environment, it is especially suitable for work in public buildings, such as schools, hospitals and offices. Only the rooms located in the immediate vicinity of the treated wall are exposed to noise and vibrations generated during work.

By using an additional head to mix quartz sand with water, 500 bar equipment in the appropriate configuration can be used for water sandblasting and sandblasting of concrete structures. This is appreciated by companies that only occasionally renovate concrete structures and do not want to buy a sandblaster alone. Until now, they had to hire a sandblaster to clean the reinforcement. Now they can do the job themselves with the sandblasting head.

Low pressure wet sandblasting is expensive as you need a compressor that can be purchased from $ 40,000. The compressor creates an air stream to which the granules are fed. The pressure varies from 0.5 to 2 bar and the amount of air forced through the nozzle is approximately 2500 liters / min. This is a very economical method, although with low efficiency, is used in the conservation of monuments.

Dry sandblasting and wet sandblasting also require the use of a compressor. Specialized companies dealing with the renovation of concrete and steel structures can usually afford high investment costs. The operating pressure is 8 bar, air flow from 5,000 liters / min. and the spray material has a grain size of 0.5-1.5 mm.

A more accurate method is dry sandblasting, used to derust steel reinforcements. Its disadvantage is high dustiness, which can be reduced by adding water (wet sandblasting). Another disadvantage is the need to wash the treated surface.

Highest pressure water jet (UHP) – working pressure is 1000 to 3000 bar. It is used by specialized companies and requires high capital expenditure (PLN 120,000 to 1,000,000). Such devices consume from 11 to 100 liters of water per minute, so they must be equipped with a hydrant connection. The personnel operating such machines must be particularly well trained. Due to the very high water pressure, on the one hand, serious protective measures are taken and, on the other hand, such work is labor-intensive and tiring.

The use of the highest pressure water jet method is eg ruptures

Possibilities offered by high pressure water