The present invention relates to a dusting gun for compressed air, more specifically to a gun of the type relating to claim 1.

The application of compressed air for removal of dirt and cleaning pur¬ poses is a well-known and extensively used technique. In order to produce a concentrated and controllable air jet the usual design is a pistol-like tool equipped with an oblong air nozzle and a built-in shut-off valve• The shut-off valve is manually operated via a pawl or similar trigger me¬ chanism mounted in connection with the handle of the dusting gun. When the trigger mechanism is activated a concentrated air jet is let out through the nozzle, and by pointing this air jet on the object to be cleaned it is possible to loosen and blast off dirt and impurities, such as dust, earth, oily coats, etc. The ability of the air jet to loosen old dirt and stick¬ ing coats of various kinds depends on the dynamic pressure exerted by the jet, i.e. primarily the jet velocity. The greater the velocity the better the cleaning effect.

However, the jet velocity is limited to the available air pressure, usual¬ ly 6 bar, and consequently an' increase in the cleaning effect can only be achieved by increasing the air flow. Especially for the purpose of re¬ moval of sticking, thick coats the air consumption will easily be dispro- portionately large, and the cleaning method therefore uneconomical.

The basis of the present invention is the desire to improved the loosen¬ ing and cleaning effect of the dusting gun in relation to especially firmly sticking impurities and at the same time achieve economy in the consumption of compressed air. According to the invention this is achieved by designing the blasting gun as described in the characterizing part of claim 1.

The oscillating shut-off valve in the dusting gun has the effect that the compressed air - instead og being ejected as a continuous air jet through the nozzle - is here split up into a series of short pressure gusts, more specifically as a pulsating air stream with periodically repeated pressure discharges. These periodical pressure discharges - by way of example with frequencies of 10-20 Hz - involve a time related concentration of the pressure energy of the air so that the peak value of the dynamic pressure

of the air in the individual discharge is increased as compared to the dynamic pressure that would be achieved, if the same volume of air was ejected continuously through the nozzle. As already stated, the dynamic pressure in the air jet determines the ability of the air to loosen stick- ing impurities and coats.

In addition to the greater dynamic pressure, the pulsating air jet also has the surprising effect of almost setting the impurities in vibrating motion under the influence of the air pulses. In the case of certain types of impurities and coats, practice has shown that this effect to a high de- gree contributes to increasing the cleaning effect of the dusting gun, as the vibrations cooperate in loosening the substances so that the cleaning operation is much faster, more thorough and more economical with the con¬ sumption of compressed air. The dusting gun according to the invention is therefore supposed to a certain extent to be able to replace traditional high-pressure cleaning (water-based jet cleaning) with the advantages this entails, both with regard to economy and environmental protection.

A preferred embodiment of the dusting gun according to the invention is described in claim 2. The mode of operation of the oscillating shut-off valve is as follows: In the normal starting position the valve body is held against the valve seat in its closing/sealing position by the coil spring. When compressed air is admitted (by activation of the trigger me¬ chanism of the gun) the pressure is increased on one side of the piston. The pressure exceeds the spring power and the valve opens, which results in a momentary discharge of compressed air and a fall in the pressure. The valve therefore closes again and the cycle is repeated. Oscillation -con¬ tinues as long as compressed air is admitted to the valve, i.e. as long as the trigger mechanism is kept activated. The valve thus gives an automatic alternating opening and closing - under the influence of the static and dynamic pressures of the compressed air - of the passage cf air in the dusting gun.

The oscillation action of the valve body presupposes a suitable balanced condition between valve dimension, the mass of the valve body (= the moving mass) and the characteristics of the spring. It is also essential that the valve body can move freely, i.e. with low friction. The frequency

depends on these factors in combination with the pressure of the com¬ pressed air.

According to the invention the piston seal can with advantage be embodied as described in claims 3 and 4. In this design the sealing arrangement satisfies the demand for low friction and ease of valve movement. An ex¬ pedient measure would be to supply the valve seat or the valve body itself with a rubber-elastic coating as described in claim 5 with a view to noise level and long life of the valve.

The dusting gun according to the invention can, like any ordinary com- pressed air dusting gun, be combined with an ejector for the supply of liquid or grainy material together with the air, cf. claim 6. The combi¬ nation of pulsating compressed air and an additive consisting of an agent for cleaning or solution gives a powerful increase in the cleaning effect. This procedure is used in special cases where such increase in efficiency is demanded.

The invention will be explained further in connection with the drawing in which

fig. 1 is a side view of a compressed air dusting gun according to the invention,

fig. 2 is an enlarged sectional view of a jet nozzle of this dusting gun,

fig. 3 is a separate, enlarged longitudinal section of the oscillatory shut-off valve of the dusting gun,

fig. 4 shows an ejector nozzle intended for use with addition of a liquid simultaneously with the compressed air,

fig. 5 is a similar ejector nozzle intended for sand blasting.

fig. 6 is a combined ejector/mixer valve with connections for air and two different liquids simultaneously.

In the embodiment shown in the drawing fig. 1 the dusting gun consists essentially of a handle section 1 (pistol grip) with a trigger lever 2 and trigger guard 3, an extension barrel 4, and an exchangeable nozzle pipe 5. The nozzle pipe has an exchangeable nozzle bit 6. The latter is shown separately in fig. 2. The handle section 1 contains a not shown shut-off valve, which opens by means of a trigger leaver 2, and an oscillatory pressure discharge valve. The pressure discharge valve is built into the portion of the handle section marked la. The air connection to the dusting gun takes place via a hose coupling 7. The nozzle pipe 5 is mounted on the handle section 1 by means of a knurled pipe union nut 8.

Fig. 3 is a separate sectional view of the oscillatory pressure discharge valve. The main component of the pressure discharge valve is a seat valve, whose seat is designated 9, and the valve body 10. The valve body is em¬ bodied in the shape of an oblong, rotationally symmetric body with longitudinal bore. One end of the valve body forms a cone-shaped tighten¬ ing disk 11 with a tight fit against the seat 9. A rubber coating 11a is vulcanized onto the cone-shaped part 11. The opposite end of the valve body 10 constitutes a piston 12 embedded in a cylinder 13. Between the piston 12 and the cone-shaped part 11 the valve body consists of an oblong cylindrical shaft portion 14.

The longitudinal bore in the valve body - in the drawing designated 15

- serves to connect the hindmost part of portion 13a of the cylinder 13 to the air duct 16 after the seat valve 11, i.e. to the extension barrel 4 and the nozzle pipe 5. The valve body is held home in its seat by a com- pression spring coil 17 inserted in the cylinder 13 behind the piston 12.

The other side 13b of the cylinder is connected via an excentrically posi¬ tioned, longitudinal bore 18 to an air chamber 19, which is located imme¬ diately in front of the seat valve on the pressure side of the latter. The direction of flow through the valve is shown with arrows 20.

The piston part 12 of the valve body is fitted with a low-friction tightening ring composed of a teflon disk 21 and an O-ring 22. The O-ring serves as a supporting disk for the teflon ring, which through its contact against the cylinder wall ensures the tightness of the piston.

Valve dimension, size and weight of the valve body, spring characteri¬ stics, the flow ducts' cross-sectional area, etc. are mutually adjusted so that the desired oscillatory effect is created by itself immediately on the opening of the air flow (by activation of the trigger lever 2). The oscillatory effect is explained above and will not be repeated here. During the oscillatory motion of the valve body the passage of the com¬ pressed air through the seat valve is opened and closed, and this gives rise to the desired pulse air with cyclically repeated pressure dis¬ charges. The pressure impacts from the pressure discharges are trans- mitted from the seat valve 9,11 and continues through the extention barrel 4, the nozzle pipe 5 and the nozzle head 6.

By exchanging the nozzle pipe 5 the dusting gun can be fitted with ejec¬ tors of various kinds, cf. figs. 4, 5 and 6. Fig. 4 shows a combined ejector and mixer valve for liquid. The liquid is supplied via a hose 23. The nozzle pipe of the dusting gun is designated 24. A shut-off valve incorporated in the mixer valve (the ejector) shuts off the liquid supply under the influence of the pressure of the liquid and opens again automa¬ tically when the supply of compressed air is opened.

The mixer valve can alternatively serve as an ejector, i.e. with pressure- less supply of liquid. The liquid will then be sucked to the ejector from a not shown tank or container by normal ejector effect, when compressed air is sent through the ejector.

Both as a mixer valve and as an ejector the quantity of liquid is adjust¬ able by means of a flow valve positioned at the intake opening of the ejector nozzle. The flow valve is operated via a finger union nut 23a.

Fig. 5 shows an ejector for use in sand blasting. The sand is sucked to the nozzle by the ejector effect via a tubular lance 25. By regulation of the suction air through the suction hose (the so-called false air) the flow of sand can be adjusted to actual needs. Regulation is done by means of an air flow valve (volume regulation valve) 25a built into the upper end of the sand lance.

Fig. 6 shows an injector/mixer valve 26, which in addition to an air

admission pipe 27 has two extra openings 28 and 29 for admixture of water and liquid chemicals, respectively. The design makes it possible to mix air ÷ water + chemical in one and the same jet. This combination is use¬ ful, among other things in connection with jobs requiring disinfection or 5 cleaning for grease.

The mixer valve can be used in the following combinations:

1) air only (both liquid intakes are plugged or otherwise closed),

2) air + adjustable volume of water,

3) air + adjustable volume of water + adjustable volume of chemicals, 104) air + adjustable volume of chemicals,

5) air + water soluble chemical + adjustable (cone.) chemical,

6) air drying after cleaning with water/chemicals.

The invention is not limited to the above shown and explained embodiment. Other types of oscillatory pressure discharge valves are also possible. 5 The primary idea of the invention is the conversion of the static energy of the compressed air into a pulsating, concentrated air jet with high dynamic energy content in the individual pressure discharges.