New Gas Filling Manifold

Farny decided to make a new gas filling manifold due to issues with brazing the aluminum. This time he decided to make it modular, with advice from Ron Soyland.

Farny used Castolin 190 FB solder. The aluminum must be heated to approximately 600 degrees Celsius so the solder melts immediately after touching the joint. When the solder cools down, it makes a white layer of flux that has to be filed off before soldering again. Farny initially used a gas-air torch, but it was not able to heat it enough. Instead, Farny used an oxy-gas torch and was able to heat all of the parts to make uniform welds.

The manifold itself is made of a piece of 30mm solid aluminum bar. He drilled holes through the piece in three places for the valve stems, which are machined from mild steel. The holes are then threaded for bass fittings to hold the valve stem packing, and on the other side the valve seat.

The fitting for the seat has the inlet connection for the gas connection. He used 7mm copper tube fittings for all the connections. To avoid leaks, capillary tubing is soft soldered to the fittings so it is hermetic with no leaks at all. The baratron is mounted to the side of the manifold.

This setup allows three types of gas to be added at a time to a tube without having to remove connections and purge out the air. This is important if using an expensive gas like xenon, where purges can be very expensive.

The copper tubing fittings are for copper flare connections, like those used in refrigerators and fuel lines. The size is 6mm, and is commonly available.

The valve manifold is also made from a piece of 30mm aluminum bar, and can be made long enough to have however many valves as desired. For example, 3 can be used to allow helium, neon, and argon to be simultaneously admitted to the tube. The basic valve consists of a 4mm hole drilled straight through, one side to the other. The same setup is used to drill the hole out larger for the threads of the fitting. These are 1/8” pipe threads. This is done on both sides of the manifold, which gives a hole with a bottom in it for the teflon washer to seal to.

The seal to the outside is done with teflon washers. These are thick enough so that when the fitting is tightened into the thread, it compresses the teflon solidly, forming a perfect seal. This can take some trial and error to find the thickness of teflon washer to seal it without closing off the hole.

The seat of the valve is made by turning the stem into the teflon, letting the point on the stem make the hole. This way the hole is exactly centered on the stem. The steel easily punches through the teflon.

The stem is machined in one operation on a piece of soft steel rod. The surface where it seals through the teflon should be polished carefully.

The point on the stem is made to be a long taper with a sharp point so it will pierce the teflon when the seat hole is made.

The black gauge above is the baratron, it measures a vacuum on a scale of 0-1.93368 psi.

Below is a diagram of the needle valve by Ron Soyland.