Mechanical Purge vs Air Purge

Mechanical Purge Spray Guns

Mechanical purge serves two functions in a spray gun. A valving rod is set inside the mixing chamber of the gun. When the gun is not triggered, the valving rod remains static and closes of the two chemical ports. When the gun is triggered, the valving rod withdraws, opens up the two chemical ports to let the polyol resin and isocyanate materials into the gun to mix and spray. When the trigger is released, the rod comes forward closing off the two chemical ports and mechanically purges the remaining mixed material out of the gun.

Mechanical Purge Operation Diagram

Mechanical Purge Spray Foam Gun Animation
Mechanical Purge Polyurea Spray Guns use a Moving Valving Rod to Purge Mixed Materials

Air Purge

Air purge guns work similar to mechanical purge guns, except they purge the material from mixing chamber and gun block using a quick blast of air. Instead of fixed mixing and a moving purge rod, like a mechanical purge gun uses, the air purge gun uses a moving mixing chamber to valve the material flow on and off.

Air Purge Operation Diagram

Air Purge Spray Foam Gun Animation
Mechanical Purge Polyurea Spray Guns use a Moving Valving Rod to Purge Mixed Materials

Solvent Purge

Solvent purge is not that common and requires flushing of a cleaning solvent through the gun to neutralize the chemical reaction and the wash out the inside of the gun. This not favorable due to the fact that solvents cost additional money, they need to be properly disposed of (costing more money), and they can be harmful to the operators and the environment, if not handled properly.