Cleaning a spray gun

Spray painting is efficient and fast. However, to achieve a flawless application, the unit must be maintained with great care.

The opening diameter of the nozzle depending on the viscosity of the product to be sprayed is to be chosen (calibre : 1,4 ; 1,7 ou 2,5 mm). A small diameter is preferred for very fluides products.. You must purchase a complete set (nozzle, needle and cap) for each use.
• Always use a solvent that is compatible with the paint, otherwise the formation of lumps may clog the gun’s ducts. Never fully immerse the unit in the diluent.

Gun cleaning is essential for trouble-free paint spraying. The unit has internal ducts and “chambers” that can become clogged if the paint dries. A further disadvantage if no maintenance is carried out is that particles can become detached and form coarse grains on the surface to be covered.

 

Suction or gravity models

Pneumatic guns are operated by compressed air to atomize the paint/thinner mixture in the bucket. There are two models: the suction gun (the bucket is located under the light alloy body) and the gravity gun (the bucket is fixed on top, our example).

 

The spray head

 

 

 

The device also has a spray head (at the front) consisting of three parts: the nozzle, the needle and the cap (photo opposite).

  • The nozzle allows the paint to pass through a calibrated orifice. It is screwed onto the inner paint supply pipe. The choice of the nozzle diameter is related to the nature and fluidity of the product, as well as to the flow rate to be obtained.
  • The needle is the moving part that closes the nozzle orifice and thus allows the passage of the paint to be opened or closed. It is actuated by a trigger and its back and forth movement, adjustable by a screw, influences the exit of the jet. On the side of the handle, a valve allows you to adjust the shape of the jet (flat or round).
  • The cap from which the compressed air exits through four orifices covers the nozzle. It is screwed with a ring to the body of the gun.

 

Each paint has its own solvent

The type of solvent used for both mixing and cleaning the unit varies according to the type of paint. For car bodies, polyurethanes with cellulosic thinner are used. Glycerol paints are used with white spirit. Cleaner and more environmentally friendly, water-based products are simply diluted with water.

After the work is completed, the excess paint in the bucket is kept in a tightly closed jar. To gently remove the needle, it is necessary to unscrew the adjusting screw and remove the spring. The parts are then soaked in the appropriate thinner.

In the case of suction guns, it is always necessary (in addition to the operations mentioned above) to clean the pipette which penetrates into the cup where there is always a bottom of product remaining.

Structure of a paint spray gun

Structure of a paint spray gun

 

The spray nozzle is placed in the centre hole of the cap.. It is screwed by a ring to the body of the gun, which receives the bucket.  The reciprocating movement of the needle is adjustable by means of a screw.

 

 

Removing the spray head

Removing the spray head

 

The spray head often clogs. To disassemble, remove the cap by unscrewing the ring, then remove the nozzle with a special wrench. Soak for several hours in the thinner.

 

 

Unclog the hat holes

Unclog the hat holes

 

The cap has four orifices that spray compressed air. They are unblocked with a rigid tip like here a brass wire from a wire brush.

 

 

Clean the bucket after use

Clean the bucket after use

 

Immediately after use, clean the surface of the bucket with a cloth soaked in thinner. Carefully scrub the inside of the cover, insisting on the part that screws on.

 

 

Clean with thinner

Clean with thinner

 

Equipped with a mask, half fill the cup with diluent, shake and spray the liquid into a bucket. Repeat the operation several times. Wipe with paper towels.

 

 

Unclog the holes in the cover

Unclog the holes in the cover

 

The lid of the bucket has a cap with two small holes (air intake). They must never be obstructed. If so, unclog them with a wire.

 

 

Facilitate trigger and needle movement

Facilitate trigger and needle movement

 

Apply a few drops of Vaseline oil with a burette to the axis of the trigger and the needle. Their movement must be supple so as not to tire the hand.

 

Source : https://www.systemed.fr/fiches-bricolage/nettoyer-pistolet-a-peinture,28.html

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