This invention generally relates to a device for cleaning wall surfaces. More specifically, the irfvention concerns a device for cleaning the walls of a pool, such as a swimming pool or a spent-fuel pool in a nuclear power plant.

Cleaning the walls of the swimming pool and the spent-fuel pool is part of the necessary maintenance work in a nuclear power plant. There are various prior-art methods and devices for doing this. Thus, the walls of the swimming pool can be cleaned manually, in which case one or a few workers in protective clothing are lowered into the emptied swimming pool in order to clean the walls with the aid of cloths impregnated with suitable chemicals, such as acetone. It will be appreciated that this is time-consuming work, which furthermore is carried out in a radioactive environment exposing the workers to radiation.

Moreover, use can be made of high-pressure washing. In practice, it has however been found that high-pressure washing does not give satisfactory cleaning results, even when aggressive chemicals are used.

In another prior-art method, the walls of the swim¬ ming pool are initially covered with a detachable layer of paint. US-A-4,351, 132 however discloses a method and a device that have been found to work satisfactorily. According to the US specification, a remote-controlled device equipped with rotating brushes is suspended by means of a three-point yoke from one of the cranes or telphers of the nuclear power plant. The pressure with which the brushes are applied against the pool wall can be increased by rotating the crane and displacing the centre of gravity of the device. The walls of the swim¬ ming pool are cleaned by the workers controlling the

crane in such a manner that the. device is moved along the walls. This' method has the considerable advantage over the other prior-art methods mentioned above that the workers do not have to stay in the pool for long but are able to control the cleaning operation from a saf'e place. However, also this method has its disadvantages. For in¬ stance, cleaning of the walls of the swimming pool or the spent-fuel pool cannot, as a rule, begin until the pool has been emptied. Since a large quantity of liquid has to be drawn off and treated, e.g. by filtration, it takes a relatively long time to empty the pool. Even though the workers naturally are not idle while the pool is being emptied, cleaning does not begin until the pool has been substantially emptied of liquid. Another disadvantage is that the crane carrying the cleaning device will be occu¬ pied during the cleaning operation and, hence, cannot be used for other tasks.

One object of the invention is, therefore, to pro¬ vide a remote-controlled device which is adapted for cleaning the walls of a swimming pool or a spent-fuel pool in particular and which can be operated without resorting to the crane of the nuclear power plant.

Another object of the invention is to provide a device enabling the cleaning operation to start when emp- tying of the pool begins.

A further object of the invention is to provide a device in which the engagement pressure is readily ad¬ justable when the device is moved along the pool walls. These and other objects are attained by a device as defined in appended claim 1. Variants and special embodi¬ ments are stated in the appended subclaims.

An embodiment of the invention will now be described with reference to the accompanying drawings, in which Fig. 1 is a schematic top view of the inventive device for cleaning the walls of a swimming pool or a spent-fuel pool,

Fig. 2 is a side view of the device in Fig. 1, taken in the direction indicated by the arrow A,

Fig. 3 is a side view of the device in Fig. 1, taken in the direction indicated by the arrow B, and Fig. 4 is a perspective view of the device in Figs 1-3, shown when cleaning a swimming pool wall.

The drawings illustrate one embodiment of the inven¬ tive device 2 for cleaning the walls of e.g. a swimming pool. The device 2 comprises a floating body 4 equipped with propelling means 6. The illustrated embodiment has two propelling means in the form of turbines or propel¬ lers 8, each driven by a motor 10, 12. Rudders, which consist of fixed or movable lamellae 14 substantially parallel to the water line, are provided for directing the flow generated by the propellers 8.

At the end facing away from the rudder end of the device 2, a superstructure 16 mounted on the floating body 4 supports a pair of brush rollers 18, 20 project¬ ing from the outside of the device 2. In the illustrated embodiment, the brush rollers 18, 20 are essentially ver¬ tical and are arranged in spaced-apart relationship at the corner areas of the device 2 facing away from the rudder end. It is evident from Fig. 3 in particular that the brush rollers 18, 20 also project from the long side of the device 2, which considerably facilitates cleaning at the corner areas of the swimming pool (see also Fig. 1). Conveniently, the brush rollers 18, 20 are so mounted in the superstructure 16 that the bottom ends of the brush rollers 18, 20 facing the surface of liquid S in the swimming pool are located at a slight distance D

(e.g. 75 mm) above the surface of liquid S. The rotatable brush rollers 18, 20 are driven by, respectively, a motor 22 and a motor 24.

It is clear from Fig. 2 that the brush roller 18 is driven with the aid of a transmission means in the form of a belt 30 passing over two pulleys 26, 28. The one pulley 26 is fixedly connected to the shaft of the brush

roller 18, whereas the other pulley 28 is fixedly con¬ nected to the shaft of its drive motor 22. As appears from Fig. 2, the propeller shaft is driven with the aid of an angular gear 32. As appears from Fig. 1, the illustrated embodiment of the inventive device is equipped with spray nozzles 38, 40 which are directed, respectively, towards the wall 34 of the swimming pool and towards a contact area 36 between the wall 34 and the respective brush rollers 18, 20 and which are adapted for spraying washing liquid, such as water, from a washing appliance (not shown).

Cables and/or hoses required for actuating and ope¬ rating the device 2 are introduced into the device 2 through a connecting means or lead-in means 42 enabling the device 2 to be continuously rotated through 360°. Al¬ ternatively, the device may be equipped with accumulators for driving motors, thus enabling use of the device without any remote-control cables. It should also be ob¬ served that air-powered motors may be used instead of electric ones.

The illustrated device 2 is provided with a mass 44 which is movable in the longitudinal direction of the device 2 and serves to displace the centre of gravity of the device 2. The provision of the movable mass 44 en- ables the device to be retained in an essentially hori¬ zontal position on the surface of liquid even when in operation, the propellers 8 having a tendency to raise the front end of the device, as is the case with ordinary motor boats. The ability to displace the centre of grav- ity of the device 2 is particularly useful when the device has fixed rudder lamellae 14.

The device 2 is placed on the surface of liquid S in the container or pool whose walls are to be cleaned (in this case the swimming pool of a nuclear power plant) be- fore emptying the pool. Use is conveniently made of an existing crane, which will be available for other tasks once the device has been placed on the surface of liquid

S. Owing to the floating body 4, the device 2 floats on the surface of liquid S and can be operated by actuating the motors 10, 12 for driving the propellers 8. To be able to control the speed of the motors 10, 12 is espe- cially convenient, making it possible to steer thfe device 2 towards one of the pool walls 34, e.g. to the position shown in Fig. 4, or towards the wall of some object pre¬ sent in the pool.

By actuating the motors 22, 24, the brush rollers 18, 20 are caused to rotate about their essentially ver¬ tical axes. The pressure with which the brush rollers 18, 20 are applied against the wall 34 is produced and ad¬ justed by actuating the propelling means 6 of the device 2, i.e. the propellers 8 in the illustrated embodiment. It will be appreciated that the one propeller 8 may have a higher or lower speed than the other propeller. As a result of such an arrangement, the device 2 tends to turn, which means that the engagement pressure is higher for the brush roller 18 or 20 located on the same long side as the higher-speed propeller, which generates a stronger propelling force.

According to the invention, the device 2 is moved in the lateral direction by imparting different directions of rotation to the brush rollers 18, 20 and altering their engagement pressures against the wall 34. It is to be understood that the device 2 does not move in the lat¬ eral direction if the propellers 8 have essentially the same speed and the rudders have essentially the same po¬ sition, in which case the brush rollers 18, 20 are ap- plied against the wall 34 with essentially the same pres¬ sure. When the one propeller 8 is given a higher speed, the device 2 tends to turn about its centre of gravity, thus increasing the engagement pressure between the wall and the brush roller located on the same side as the higher-speed propeller and reducing the engagement pres¬ sure between the wall and the other brush roller. Thus, the force component generated between the former brush

roller and the wall in the direction of rotation of the brush roller will exceed the force component generated between the latter brush roller and the wall. As a result of the difference in engagement pressure, the device will move laterally in a direction determined by the (direction of rotation of the brush roller at issue. By imparting different directions of rotation to the brush rollers 18, 20, the device can thus be moved laterally along the wall 34 in both directions while cleaning the latter. Naturally, the directions of rotation and/or speeds of the brush rollers may be varied also with a substan¬ tially constant engagement pressure. This will result in the generation of a more or less considerable force com¬ ponent along the wall, tending to move the device in the lateral direction.

The walls of the pool, or the surface of an object present in the pool, are cleaned while the pool is being emptied of its content. For the reasons indicated above, the emptying rate may be restricted, which means that a suitably-dimensioned device takes a turn round the pool while the level of liquid in the pool sinks. The differ¬ ence in level ΔH of the surface of liquid before and after the device has taken a turn round the pool does not exceed the height of the brush roller. Thus, the device performs a substantially helical movement until the pool has been emptied and the device comes to rest on the pool bottom, whence it is lifted up by means of the crane men¬ tioned above.

It will be appreciated that the inventive device is highly efficient when cleaning pool walls or other sur¬ faces, in particular if water is sprayed onto the wall when the brushes are in operation. The inventive device not only saves time but also requires a small labour input, since cleaning actually takes place while the pool is being emptied and since the device requires practi¬ cally no monitoring owing to its design and mode of op¬ eration.

It goes without saying that those skilled in the art may devise alternative embodiments and other means pro¬ ducing the same technical effect and thus being encom¬ passed by the basic inventive concept. Thus, the propel- lers may be replaced with turbines located below ^τ or above the surface of liquid. If so desired, the turbine flow can be controlled. Furthermore, it will be appreciated that, although the brush rollers should be situated in a plane parallel to the wall, they do not have to be verti- cal but may form an angle with the surface of liquid. In addition, a brush roller essentially parallel to the sur¬ face of liquid may be provided on a level with or just below the surface of liquid. Also, the two vertical brush rollers may be replaced with a plurality of brushes ar- ranged on a belt, in which case the brushes successively come into contact with the wall. Thus, all such altera¬ tions and modifications are intended to be encompassed by the scope of protection claimed.

Finally, it should be emphasised that the word "walls" does not only refer to the boundary walls of a pool. Naturally, the inventive device may be used for cleaning the surface of an object extending upwards from the centre of the pool, such as the hull of a docked ship.