1.  Field of the Invention
An abrasive cleaning apparatus having a horizontal positioning means and a vertical positioning means to permit movement of a plurality of nozzles both horizontally and vertically relative to a work surface. 
2.  Description of the Prior Art
Sand blasting of surfaces cleaned preparatory to painting and simply cleaning in the case of stone or brick walls is a common practice.  Generally, this is accomplished by an operator positioned on a scaffold or other suitable support to manually manipulate at least one discharge nozzle.  Obviously the presence of the operator in the work zone makes this an extremely dirty and hazardous occupation.  Moreover, the limited volume of sand blasted against the surface by a single nozzle is very inefficient. 
As a result, abrasive blast apparatus, particularly used for large surface areas may employ multiple rather than a single blast nozzle.  The obvious advantage of this being a greatly increased blast pattern.  Due to the increased weight and speed of operation, these nozzles are often mounted on movable carriages or platforms on which the operator rides.  The platform is movable laterally and vertically along the area to be cleaned which results in significant labor saving devices. 
Unfortunately, a number of difficulties have been experienced which hindered general acceptance and wide use for the multi-nozzle head.  For example, many multi-nozzle heads are of a type in which the sand and air are delivered and mixed in a common reservoir from which jet streams are propelled simultaneously from the nozzles all of which communicate directly with the reservoir.  In another configuration, the operator may be provided with two separate nozzles each having its own supply lines.  In either of these arrangements, individual control of the nozzles is lacking to the extent that the blast stream from one nozzle cannot be cut off independently of the other.  Such independent manipulations of the blast from the different nozzles is desirable in situations involving spots or areas which present difficult cleaning problems.  The blast from one nozzle must work on this different area for a prolonged period, during which time the other blasts will be cutting away injuriously at the metal or surrounding areas. 
Another difficulty with previous multi-blast carriage arrangements is that the units are very cumbersome and complex so as to be suitable only for special cleaning operations.  Also many such multiple nozzle machines have lacked adequate flexibility of movement and could not be easily manipulated. 
Once there is developed an efficient abrasive cleaning apparatus which is able to position the plurality of nozzles both horizontally and vertically relative to a work surface, it is still desirable that the nozzles be adjusted angularly relative to the work surface so that the most efficiency is attained by the blasts from the nozzles against the work surface. 
Thus, there is a clear need for an efficient, flexible and easily moved multiple nozzle blasting apparatus.