The hand vacuum pump is connected to the other end of the tubing, and fortunately includes a built-in vacuum release mechanism, which is required to release the vacuum when finished with a test.
Also notice that a multi-conductor cable is going into the chamber as well as the hose. This is for testing electronic device in the chamber while having the test equipment outside the chamber. Note that unless the inner conductors of a multi-conductor cable are very tightly enclosed by the outer jacket that some vacuum leakage may occur.
Here the complete system is shown, mounted on a board to make the system easy to move. A much better physical arangment could of course be chosen if room permits.
The hand pump was retained to provide a fine adjustment of the altitude and also includes a convenient vacuum release mechanism.
The vacuum gauge was included because it was available from the purchase of the original hand vacuum pump and because it could be useful in future experiments related to pressure and not altitude. It also includes a vacuum release mechanism, which is needed somewhere is the vacuum line.
A closeup shows the hose and fittings. The fitting used at the pump was made by soldering a hose barb fitting to a threaded fitting that matched one of the two different fittings on the pump. If standard fittings and hoses were used instead of the vinyl tubing this would not be necessary.
The chamber uses a fitting threaded on one end and with a hose barb on the other end. This connector was screwed into a hole in the chamber (which was made just large enough to allow the fitting to make its own shallow threads), and was then sealed with silicone sealer (RTV).
The hand vacuum pump used was a Neward Enterprises Mityvac. There are a number of models of the Mityvac and one is available from McMaster-Carr, currently about $90 including the vacuum gauge and accessories.
Many different types of electric vacuum pumps were researched. Although it would seem like there should be numerous small and inexpensive vacuum pumps available similar to aquarium air pumps, these provide only pressure, not vacuum. The type of vacuum pump that was found to be the most appropriate, affordable, and available is designed for the air conditioning service industry, to evacuate a line in preparation for adding refrigerant.
The electric vacuum pump used was the Advanced Tool Design ATD-3409 1.5 cubic foot per minute pump, found one at an online tool supply company for about $100. ATD also makes the ATD-3425 5 cubic foot per minute pump which would probably be needed for applications using a large volumn chamber, for example, if a chamber was needed to hold a complete rig.
1/4 inch inside diameter (3/8 inch outside diameter) vinyl tubing was used because that is what the original hand vacuum pump was designed for, but if only an electric vacuum pump is used, more standard sizes and types of tubing and fittings could be used. Miscellaneous hose fittings, such as barbed splicers, barbed T's, etc., were used on the vacuum connections. Hose and fittings were found at a home supply store.
Both the hand vacuum pump and the vacuum gauge have a built-in vacuum release mechanism, which is a required component in the system. If an electric vacuum pump is used that does not have a vacuum release, one can probably be found in the same place as the hose fittings.