Parks College Parachute Research Group

Vacuum Chamber for Testing Pressure and Altitude Related Devices

vacuum chamber system



This article provides detailed information and pictures describing the vacuum (altitude) chambers built and used by the PRG and by Industrologic, Inc. for testing pressure and altitude related devices. The original altitude chamber system used for many years consisted of a small plastic storage container, a hand operated vacuum pump, and some tubing and fittings. Later a larger container was added, and more recently an electric vacuum pump. This information is now being provided to help others build their own chamber. For questions or comments you may contact Gary Peek at peek@pcprg.com.

Original chamber

The original chamber was chosen because it has a nice latching mechanism for the lid that makes it very tight. A closeup view of the top shows that this chamber does not use a hose fitting for the tubing. The tubing simply goes through a hole and is sealed with silicone sealer (RTV). This method works well if the sealer is applied skillfully, and can be easily reworked if the seal fails due to too much movement of the tubing.

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.

Later chamber

After it was realized that the original chamber did not have enough room for some of the required work, a larger container was added. A larger container meant that a larger volumn of air needed to be removed to obtain the same altitude as the smaller container. The hand pump continued to be used for a while but eventually an electric pump was needed. To complete the upgrade to the entire system an aircraft altimeter was purchased to provide increased accuracy to the altitude measurements.

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).

Components and construction notes

The chambers were made from plastic storage containers with latching lids designed for storing and sealing food. These were found at a department store, although a larger selection might be found at a "kitchen and bath" specialty store.

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.

Other Resources

The Bell Jar

Warning/Disclaimer:

The described vacuum chambers made from plastic storage containers have not been tested to any particular vacuum. Under certain conditions it is possible to create enough vacuum to damage (implode) a chamber. Anyone who designs, builds, and uses a vacuum chamber is responsible for its safety during use. If you have any doubt about the safety of a vacuum chamber you must include in the system design a barrier of sufficient strength and size to protect the user(s) from an implosion of the chamber. An electric vacuum pump can create a vacuum very quickly and the vacuum/altitude must be monitored closely. Use only the amount of vacuum needed to test the device inside the chamber.

log file