Details on making an altitude chamber available here

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We just upgraded our altitude chamber (for testing altimeters, etc.) with a cool new electric vacuum pump, and I finally wrote an article on it, including enough details to make your own if you want.

It can be found on our Instrumentation page at:
http://www.pcprg.com/prginst.htm

Comments welcome, especially from anyone that can tell me more about what all these hose fittings are that I had to look through to find the right ones.

[councilman24 37]

Gary,

While the storage containers are easily available so are vacuum dessitcator with the hose connection built in.

An example is at http://www.belart.com/shop/420100000-space-saver-vacuum-desiccator-140mm-white-base-p-420100000.html

These are designed to take a vacuum, have the hose connection built in and offer a three way valve to be able to disconnect the pump and release the vacuum. I have one of these I use that is easily controlled with a little practice to release the vacuum at freefall rate to test AAD's.

I'd suggest that a vessel designed to take the vacuum is safer than an unknown storage container that might implode.

Also, you shouldn't need to solder a hose barb to a fitting. A hose barb with the proper threads is available, maybe not locally. But Lowes has a large selection of these kinds for fittings, including the t connectors in you system. Even if not available to connect to the pump directly adaptor unions should be available to make threaded connections.

I have a poly drum similar to these http://www.uline.com/BL_8154/Plastic-Drums that I have made into a whole rig chamber for FXC12000 testing. It still needs a clear window added to the top but I have rarely used it.

added;

If your pump is like mine it has lots of oil in it. If you leave the pump attached to the chamber and turn it off you can get oil vapor pulled into chamber. It's best to isolate the chamber and then turn off the pump.

I'm old for my age.
Terry Urban
D-8631
FAA DPRE

[riggerpaul 1]

Your links don't seem to work.

Maybe because your markups used "u" and "/u" instead of "url" and "/url".

I would have fixed it for you if it would have let me.

I cut and pasted, and I got to the sites. So I know that the text you wrote is correct.

-paul

[councilman24 37]

Fixed. I used underline instead of url for link.

I'm old for my age.
Terry Urban
D-8631
FAA DPRE

[peek 21]

Quote

Also, you shouldn't need to solder a hose barb to a fitting.

I know, but I'm a lot better at soldering than I am standing around in Lowes trying to figure out what all those fittings are.

I was hoping someone would come along and go, "Yeah, those typical A/C vacuum pumps have a so-and-so sized fitting, and here's what all that stuff is called and here's how you do it." Not expecting much am I?

Quote

If your pump is like mine it has oil in it. If you leave the pump attached to the chamber and turn it off you can get oil vapor pulled into chamber. It's best to isolate the chamber and then turn off the pump.

Good advice, I will put some filter material in the line and see how long it takes to see any oil. How long did it take until you did?

[riggerrob 643]

I have a poly drum similar to these http://www.uline.com/BL_8154/Plastic-Drums that I have made into a whole rig chamber for FXC12000 testing. It still needs a clear window added to the top but I have rarely used it.

.........................................................................

The simple answer is use a large, thick sheet of Lexan/Plexiglas for a lid .... similar to official FXC test chambers
The challenge is finding the correct brand of rubber/silicone to seal around the edge.

[councilman24 37]

The hoses on the vacuum pumps always seem to have oil in them. I can't say how long it took. Mine came from my old job. It's just not a good idea to let the vacuum suck on the oil. You may not be able to tell that your getting a thin film right away.

To Rob. I have high vacuum grease thats used to seal glass desicators. That seals thinks like lexan lids pretty well. I was going to do the lexan lid but just have never used the drum much.

I'm old for my age.
Terry Urban
D-8631
FAA DPRE

[peek 21]

Quote

I'd suggest that a vessel designed to take the vacuum is safer than an unknown storage container that might implode.

I took it to the DZ this weekend, and after telling some of they guys that I didn't think they needed to test their altimeters any higher than 15K, after I left the room they took it up to 21K.

We found that most of the student Alti-2 Galaxy altimeters were about 200 feet low at 9K (within spec) and 2 of them were about 400-500 feet low, (which indicates sending them back to the factory would be a good idea.)

At least now I can explain with confidence the discrepancy to the students. It was driving me crazy seeing them always different from my Alti II and Alti III.

[Gary73 10]

Small world! I just built an altimeter test chamber of my own. The pump is a Barnant 400-1901 that I got new on eBay for $19.99 plus S&H. The rest is mainly stuff that I had lying around the shop, so the whole thing cost less than $50. It'll run up to 22,000 feet in under a minute, then come down at about freefall speed once the power is cut. The original plan was to include a Vertical Speed Indicator, but I couldn't find one that would handle our fall rates. Oh well, 5 - 6 seconds per thousand feet is probably close enough. It doesn't include a certified reference altimeter, but if you put three or four units in there and they all read the same, they must all be right, right?

The reason I was more concerned with vertical speed than with actual altitude is that units that read the same on the way up in the plane may not read the same on the way down in freefall. In other words, the rate at which the air pressure changes can definitely affect the reading.

Anyway, I don't have any plans or anything, since I followed my usual approach of designing it as I went along, but if anyone's interested in making a similar unit, feel free to PM me.

"Extraordinary claims require extraordinary evidence." - Carl Sagan

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That was a good price on the vacuum pump, I saw it listed elsewhere for a lot more.

It is interesting to see such a different chamber design, one designed for altimeters. Yours is a very inherently strong design.

There is a lot of difference in skydiving altimeters. Most of the older Altimaster II and III models are very accurate if they have been treated well.

Galaxy models are often a bit low, however, still in spec.

I needed the accuracy of the aircraft altimeter for things other than testing skydiving altimeters.