A siphon gun is simply an air gun that sucks up liquid into the air stream and propels the mixture out the nozzle end.
This section will explain how to make your own and the techniques to use when shrinking.
Basic parts required:
100 cfm is required for good effect. The siphon gun in this case would be using a 3/4 inch pipe nozzle. For smaller applications a siphon gun using only 1/8 pipe and using a 10 cfm air supply is adequate.
Metal can be shrunk without the application of water to cool the surrounding area however using some sort of cooling increases the effect. Partial measures include a plastic squirt bottle of water or even a bucket and a wet rag The picture shows a homemade unit using discarded welding hose for the tubing.
The unit shown was made from scrap pieces of pipe and a ball valve purchased at a local plumbing supply house. A short length of small diameter steel tube is welded to the pipe.
A hole was drilled in the side of the 1/2 inch pipe. I made it large enough so that the small steel tube would slide in easily and could be wiggled around . Strike the pipe in the area of the hole so that it is narrowed creating a venturi. Slip the small tube into the pipe while air is blasting through. By trial and error the "sweet" spot can be located. Tack weld the tube in position and then check before welding up solid.
If the draw of water is excessive then make up some sort of clamp to squeeze the rubber hose in order to restrict the flow of water. Ideally you want just enough water to increase the cooling effect of the air blast without dumping tons of water that will end up as puddles on the floor.
The main thing to understand when using a siphon gun when shrinking is not to quench the red area. The goal is to keep the area surrounding the red as cool as possible. Slowly move the blast around the perimeter, moving in toward the red as the metal turns black.