Spray guns are widely used in vehicle body repair shops when re-spraying a vehicle that has been repaired following an accident. In the known spray guns, the liquid is contained in a reservoir attached to the gun from where it is fed to a spray nozzle. On emerging from the spray nozzle, the liquid is atomised and forms a spray with compressed air supplied to the nozzle. The liquid may be gravity fed or suction fed or, more recently, pressure fed by an air bleed line to the reservoir from the compressed air line to the spray gun.
Traditionally, the liquid is contained in a rigid pot detachably mounted on the spray gun and is delivered to the spray nozzle under the control of a manually operable trigger mechanism on the gun. On completion of spraying, the pot is removed and the gun and pot cleaned for re-use.
With this arrangement, the gun and pot must be thoroughly cleaned with solvents to remove all traces of the liquid to prevent cross-contamination with the next liquid to be sprayed. Particular problems arise when cleaning the gun to ensure no deposits are formed within the gun that may affect the operation of the gun. As a result, the spray nozzle may have to be dis-assembled to enable the spray nozzle and internal passageways of the gun to be properly cleaned. This is time consuming and the use of solvents is undesirable from health and safety considerations and causes problems for disposal of the solvent after use.
We have recently developed a system in which the reservoir is disposable after use thereby reducing the amount of cleaning required on completion of spraying. With this system, however, the spray gun including the spray nozzle must still be cleaned to remove all traces of the liquid before the gun is put away or before spraying another liquid.
DE-A-4302911 discloses a paint spray gun having a replaceable single-use spray nozzle releasably secured to the spray gun body allowing the spray nozzle to be removed after use and replaced by a new spray nozzle. The spray nozzle has an integral (built-in) needle valve shaft which acts as an open close valve and a branch tube for supply of liquid to be sprayed. The rear end of the spray nozzle is inserted into the spray gun body and is secured by tightening a transverse bolt to engage the rear end of the spray nozzle. The needle valve shaft is connected to a trigger mechanism within the spray gun body by tightening a clamping sleeve to engage the free end of the shaft. A pair of opposed inwardly directed air streams are provided by a cap nut screwed onto the spray gun body separate from the spray nozzle.