Portable surface cleaning apparatus comprising a base; a tank associated with said base at the top thereof, said tank being predisposed to contain at least one abrasive material; at least one mixing valve associated with said base and connected with said tank so as to receive said abrasive material contained in said tank and mix said abrasive material with a predetermined amount of compressed air; an adjusting member predisposed to enable the selection of a predetermined value indicating the amount of said abrasive material to be mixed with said compressed air in said at least one mixing valve; a shutter device associated with said at least one mixing valve; and drive means predisposed to connect said adjusting member with said shutter device, said shutter device being operable remotely by said adjusting member, through said drive means, in order to vary the amount of said at least one abrasive material to be mixed with said flow of compressed air of a value proportional to said value indicating the amount of said abrasive material, said drive means including a drive shaft associated with an end of said adjusting member, said drive shaft being operable in rotation by said adjusting member around a first axis, in order to perform manually adjusting operations of said amount of said at least one abrasive material to be mixed, characterised in that: said drive shaft is associated at an opposite end with a gear assembly predisposed to transmit the motion from said drive shaft to said shutter device; said first axis, around which said drive shaft is operable in rotation, is basically longitudinal to said apparatus and said gear assembly comprises orthogonal axes gears predisposed to transmit the rotation motion from an input shaft, substantially coaxial to said drive shaft, to an output shaft, associated with said shutter device, said output shaft being operable in rotation about a second axis transversal to said first axis. a base; a tank associated with said base at the top thereof, said tank being predisposed to contain at least one abrasive material; at least one mixing valve associated with said base and connected with said tank so as to receive said abrasive material contained in said tank and mix said abrasive material with a predetermined amount of compressed air; an adjusting member predisposed to enable the selection of a predetermined value indicating the amount of said abrasive material to be mixed with said compressed air in said at least one mixing valve; a shutter device associated with said at least one mixing valve; and drive means predisposed to connect said adjusting member with said shutter device, said shutter device being operable remotely by said adjusting member, through said drive means, in order to vary the amount of said at least one abrasive material to be mixed with said flow of compressed air of a value proportional to said value indicating the amount of said abrasive material, said drive means including a drive shaft associated with an end of said adjusting member, said drive shaft being operable in rotation by said adjusting member around a first axis, in order to perform manually adjusting operations of said amount of said at least one abrasive material to be mixed, characterised in that: said drive shaft is associated at an opposite end with a gear assembly predisposed to transmit the motion from said drive shaft to said shutter device; said first axis, around which said drive shaft is operable in rotation, is basically longitudinal to said apparatus and said gear assembly comprises orthogonal axes gears predisposed to transmit the rotation motion from an input shaft, substantially coaxial to said drive shaft, to an output shaft, associated with said shutter device, said output shaft being operable in rotation about a second axis transversal to said first axis. said drive shaft is associated at an opposite end with a gear assembly predisposed to transmit the motion from said drive shaft to said shutter device; said first axis, around which said drive shaft is operable in rotation, is basically longitudinal to said apparatus and said gear assembly comprises orthogonal axes gears predisposed to transmit the rotation motion from an input shaft, substantially coaxial to said drive shaft, to an output shaft, associated with said shutter device, said output shaft being operable in rotation about a second axis transversal to said first axis.