Forums: Skydiving: Gear and Rigging:
Has anyone built their own altimeter chamber?

 


377  (F 666)

Feb 5, 2008, 10:26 PM
Post #1 of 19 (1125 views)
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Has anyone built their own altimeter chamber? Can't Post

Any tips on construction? I have a vacuum pump, some tubing, connectors and valves and some rough ideas. Would like to hear from anyone who has built their own so I can benefit from their successes and failures. Thanks for your help, Mark


councilman24  (D 8631)

Feb 6, 2008, 5:46 AM
Post #2 of 19 (1058 views)
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Re: [377] Has anyone built their own altimeter chamber? [In reply to] Can't Post

These work pretty well.
https://new.fishersci.com/...pi=y&fromSearch=
You can actually get one for about $90.


Glass ones are available also. But the ground glass surface between the lid and bowl needs vacuum grease to seal. This makes it kind of messy.
http://cgi.ebay.com/...QQrdZ1QQcmdZViewItem

A friend paid way too much money to have a local plastics fabricator use acrylic (maybe polycarbonate) tubing to make a chamber. End plate glued to one end. Plate with hinge and circular dado with o-ring on the other end. A little work with a router and plastic glue and you can do this yourself.

I also added a port to a plastic drum sealed with an oring so I could test FXC installations on entire rigs.

But, I also saw these recently.
http://cgi.ebay.com/...QQrdZ1QQcmdZViewItem

Pump built in. May work fine for altimeters check.


(This post was edited by councilman24 on Feb 6, 2008, 5:51 AM)


skybeergodd

Feb 6, 2008, 6:50 AM
Post #3 of 19 (1037 views)
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Re: [377] Has anyone built their own altimeter chamber? [In reply to] Can't Post

I know Gary Peek built one not too long ago to do some testing with cypres'. It was completely home built and worked great. He posts here once in a while under Peek.
You can catch him more often in the Instructor or S&TA forums though.


stratostar  (Student)

Feb 6, 2008, 8:39 AM
Post #4 of 19 (995 views)
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Re: [377] Has anyone built their own altimeter chamber? [In reply to] Can't Post

Had a friend make one out of a 55 gallon drum and a plexiglass lid. Could put whole rig inside to test FXC's and the like. Worked great.

P.S. I think he added a bleed off valve on it.


MrBrant  (B License)

Feb 6, 2008, 8:49 AM
Post #5 of 19 (986 views)
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Re: [377] Has anyone built their own altimeter chamber? [In reply to] Can't Post

Check out here:

http://forum.altimaster.com/showthread.php?t=117


377  (F 666)

Feb 6, 2008, 12:22 PM
Post #6 of 19 (938 views)
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Re: [councilman24] Has anyone built their own altimeter chamber? [In reply to] Can't Post

Thanks to EVERYONE who responded. Super helpful info!!!! Nice to be on a forum that helps rather than flames. Now I have a much better idea of where to start on my vacuum chamber project.

I am going to initially try to make one with a 12 volt vacuum pump from a car cruise control system so that it could be used on the DZ with a small 12 volt battery. Not yet certain if those kind of pumps will pull enough vacuum but if not I'll find one that does. The nice thing about the cruise pumps is that they are so cheap used and very small.

Mark


377  (F 666)

Feb 6, 2008, 1:01 PM
Post #7 of 19 (923 views)
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Re: [councilman24] Has anyone built their own altimeter chamber? [In reply to] Can't Post

That eBay food storage thing with the internal vacuum pump looks pretty interesting. If it can truly pull 160 mb vacuum that is more than enough to test skydiving altimeters. I guess all I would need to add is a manual switch for the pump and a bleed valve to meter a descent. I think I'll try this before re-inventing the wheel. Thanks for the info!


(This post was edited by 377 on Feb 6, 2008, 1:16 PM)


councilman24  (D 8631)

Feb 6, 2008, 7:08 PM
Post #8 of 19 (868 views)
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Re: [377] Has anyone built their own altimeter chamber? [In reply to] Can't Post

I don't have a clue if it will work. Just saw them for the first time a week or two ago.

Hand vacuum pumps for testing car vacuum systems work. Can be had with or without gauge. No batteries needed.Wink

But in reality in 30 years I don't think I've ever seen one at a DZ, other that Alti booth at WFFC. If in doubt get someone else to wear it or wear a spare to compare.

Really no need at the DZ. But it's fun to have something to tinker with.Tongue

Rigger have them to test function test FXC 12000 AAD's.


heavydude  (A 53326)

Feb 6, 2008, 7:47 PM
Post #9 of 19 (856 views)
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Re: [377] Has anyone built their own altimeter chamber? [In reply to] Can't Post

We have built a number of these at work; primarily for degassing polyurethanes when casting prototype parts. Some ideas:

We made one w/ large cast AL pot, sealed top w/ Oring and 1 inch plexiglass top. Used this as temp until we did following.
Made another w/ 1 gallon paint pot, Harbor Frieght is cheapest.
Made another w/ 5 gallon paint -pot, these are expensive.
All were powered w/ standard lab type vac. pump.


heavydude  (A 53326)

Feb 6, 2008, 8:03 PM
Post #10 of 19 (852 views)
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Re: [377] Has anyone built their own altimeter chamber? [In reply to] Can't Post

By the way on pumps you can try modifying a 12 V or 120 VAC type pump by connecting it as a vac. instead of compressor. (some compressors have 1/8 NPT, 1/4 NPT inlet ports, sometimes plumbed w/ mufflers)
Pumps used for small air compressors may work this way fairly well, a check valve in-line will also help seal the vac. A bleed port is essential of course but this can be just a needle valve plumbed into the chamber. When running a electric compressor as vac. you have to be careful not to stall the compressor by trying to start it under load. (pressure/vac.) Some units will pump sufficently from an unloaded condition but not at all w/ any load. Luckily most compressors are thermally protected so they work again once cooled down.
Hand pumps are really only practical for small rigid lab bell-type jars. By the way if you use a bell jar, Dow Corning Silicone 111 is usually used to make glass jar seal to base plate.
Yes ive done all kinds of weird shit working in an engineering lab for 20+ years...


377  (F 666)

Feb 7, 2008, 12:54 PM
Post #11 of 19 (791 views)
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Re: [councilman24] Has anyone built their own altimeter chamber? [In reply to] Can't Post

In reply to:
I don't have a clue if it will work. Just saw them for the first time a week or two ago.

Hand vacuum pumps for testing car vacuum systems work. Can be had with or without gauge. No batteries needed.Wink

But in reality in 30 years I don't think I've ever seen one at a DZ, other that Alti booth at WFFC. If in doubt get someone else to wear it or wear a spare to compare.

Really no need at the DZ. But it's fun to have something to tinker with.Tongue

Rigger have them to test function test FXC 12000 AAD's.

You are right, no real need to have one in the field, just a fun thing to play with while waiting for the overcast to clear up. When I watched the one Alti 2 brought to WFFC I saw some altimeters that were way off at higher altitudes but OK at pull altitudes. It wasn't always a constant error.


377  (F 666)

Feb 7, 2008, 1:00 PM
Post #12 of 19 (784 views)
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Re: [heavydude] Has anyone built their own altimeter chamber? [In reply to] Can't Post

Heavydude, Many thanks for those very practical tips! That's the kind of stuff that matters but isnt necessarily in the books.


Lab Rats rule!


377  (F 666)

Feb 7, 2008, 1:07 PM
Post #13 of 19 (778 views)
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Re: [stratostar] Has anyone built their own altimeter chamber? [In reply to] Can't Post

In reply to:
Had a friend make one out of a 55 gallon drum and a plexiglass lid. Could put whole rig inside to test FXC's and the like. Worked great.

P.S. I think he added a bleed off valve on it.

Dont tell skydivers how to make a cheap vacuum chamber that an ex could fit in. Baaad idea. My ex is OK, and I don't pay spousal support any more, but there are others out there whose circumstances are quite different.Wink


(This post was edited by 377 on Feb 7, 2008, 1:08 PM)


Liemberg  (Student)

Feb 7, 2008, 2:50 PM
Post #14 of 19 (758 views)
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Re: [377] Has anyone built their own altimeter chamber? [In reply to] Can't Post

Quote:
cheap vacuum chamber that an ex could fit in.
And if you do, don't forget to do the math on the presures involved when you take your vacuumchamber with a complete rig or your ex in it 'all the way to 12 grand'... Smile

(Hint: We built one from a steel tube we got from people who were working as welders on gas-pipes-for-mass-transportation. Ours was sealed/covered on one side with steel and on the other with a lexan lid. At another place "that shall remain nameless" they decided that some sort of square homebuilt box of plexiglass "definitely was strong enough". They almost killed themselves finding out with a spectacular implosion that it wasn't. Just calculate kg per cm2 and see what it ads up to...)

ShockedSmileBlushCool


377  (F 666)

Feb 7, 2008, 7:17 PM
Post #15 of 19 (726 views)
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Re: [Liemberg] Has anyone built their own altimeter chamber? [In reply to] Can't Post

I have heard stories about ruptured Scuba tanks going through several walls, but I never gave much thought to the dangers of vacuums in containers that can't withstand the pressure differential. Hmmmm. Wouldn't that be a bitch to survive decades of jumping and be killed by a home made altimeter chamber???


riggerrob  (D 14840)

Feb 8, 2008, 9:11 AM
Post #16 of 19 (683 views)
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Re: [377] Has anyone built their own altimeter chamber? [In reply to] Can't Post

I have worked with a few home-made altitude chambers. They were made from steel drums, with plexiglas lids, etc.
If you want to test an AAD installed on a complete rig, then start with a 55 gallon drum (aka. fuel barrel).
The biggest hassle was getting a decent seal around the top edge.
We were constantly fiddling with different types of rubber seals.

A decade ago, my boss decided that he needed a chamber to test all his FXC 12000 AADs. After a bit of research, he concluded that paying USD3,000 for a factory-official test chamber would cost about the same as a home-made chamber with aircraft quality altimeter, variometer, pump, bleed valve, fiddle factor, etc.

If you are only interested in testing altimeters or playing around on rainy days, he will cheerfully sell you an FXC 8000 test chamber for cheap.


heavydude  (A 53326)

Feb 8, 2008, 7:29 PM
Post #17 of 19 (657 views)
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Re: [377] Has anyone built their own altimeter chamber? [In reply to] Can't Post

I went back to the shop and scoped our chambers;
seals on real cheapo chambers were 1/4 silicone sheet rubber, probably bought from McMaster Carr.
Improved models had large O-rings or silicone poured into machined grooves. I dont have my chart but pressure is about 14.7 psi at 10K feet from memory ? I will try and post some pics next week of these units. Hyperbaric chambers allot more hazardous to make, 14.7 per 33 FSW. We have one that goes to 300 FSW, has 2.0 thick S.S. walls (wasnt homemade !)Crazy


377  (F 666)

Feb 15, 2008, 2:06 AM
Post #18 of 19 (571 views)
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Re: [councilman24] Has anyone built their own altimeter chamber? [In reply to] Can't Post

In reply to:
These work pretty well.
https://new.fishersci.com/...pi=y&fromSearch=
You can actually get one for about $90.


Glass ones are available also. But the ground glass surface between the lid and bowl needs vacuum grease to seal. This makes it kind of messy.
http://cgi.ebay.com/...QQrdZ1QQcmdZViewItem

A friend paid way too much money to have a local plastics fabricator use acrylic (maybe polycarbonate) tubing to make a chamber. End plate glued to one end. Plate with hinge and circular dado with o-ring on the other end. A little work with a router and plastic glue and you can do this yourself.

I also added a port to a plastic drum sealed with an oring so I could test FXC installations on entire rigs.

But, I also saw these recently.
http://cgi.ebay.com/...QQrdZ1QQcmdZViewItem

Pump built in. May work fine for altimeters check.

Thanks for the tip Councilman. Bought the eBay vacuum food saver and it is a REALLY good start. Big interior, would even take a full sized acft alt. laid on its side (still visible) or several skydiving alts laid flat. Right out of the box it goes to 6.5K before the limit switch shuts off the pump. The closing latch serves as a decent adjustable bleed valve if you open it slowly, pretty easy to simulate freefall rate of descent. Next I will bypass the limit switch and see if I can take this to 12 or 14K of vacuum without imploding it or stalling the pump motor. You couldn't possibly build this for $20 (see his other listings, I paid $20 plus shipping) so the value is truly amazing. Takes D cells (not incl) or AC adapter (incl). Made in China but not a junky item, at least from the outside. I expect a cheap DC brush motor and a flimsy diaphragm pump inside, but hey, for $20 are you expecting a brushless motor and a gear or vane pump? You will never find a cheaper brand new self powered vacuum chamber suitable for altimeter testing. Durability? Time will tell.

This is going to seriously damage the market for high priced vacuum chambers that are used in applications where specs and approvals aren't crucial and which don't need super low vacuums. I think this may have other uses like getting bubbles out of adhesives, dessication etc. Any other ideas?


(This post was edited by 377 on Feb 15, 2008, 2:23 AM)


377  (F 666)

Feb 25, 2008, 10:23 AM
Post #19 of 19 (495 views)
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Re: [377] Has anyone built their own altimeter chamber? [In reply to] Can't Post

In reply to:
In reply to:
These work pretty well.
https://new.fishersci.com/...pi=y&fromSearch=
You can actually get one for about $90.


Glass ones are available also. But the ground glass surface between the lid and bowl needs vacuum grease to seal. This makes it kind of messy.
http://cgi.ebay.com/...QQrdZ1QQcmdZViewItem

A friend paid way too much money to have a local plastics fabricator use acrylic (maybe polycarbonate) tubing to make a chamber. End plate glued to one end. Plate with hinge and circular dado with o-ring on the other end. A little work with a router and plastic glue and you can do this yourself.

I also added a port to a plastic drum sealed with an oring so I could test FXC installations on entire rigs.

But, I also saw these recently.
http://cgi.ebay.com/...QQrdZ1QQcmdZViewItem

Pump built in. May work fine for altimeters check.

Thanks for the tip Councilman. Bought the eBay vacuum food saver and it is a REALLY good start. Big interior, would even take a full sized acft alt. laid on its side (still visible) or several skydiving alts laid flat. Right out of the box it goes to 6.5K before the limit switch shuts off the pump. The closing latch serves as a decent adjustable bleed valve if you open it slowly, pretty easy to simulate freefall rate of descent. Next I will bypass the limit switch and see if I can take this to 12 or 14K of vacuum without imploding it or stalling the pump motor. You couldn't possibly build this for $20 (see his other listings, I paid $20 plus shipping) so the value is truly amazing. Takes D cells (not incl) or AC adapter (incl). Made in China but not a junky item, at least from the outside. I expect a cheap DC brush motor and a flimsy diaphragm pump inside, but hey, for $20 are you expecting a brushless motor and a gear or vane pump? You will never find a cheaper brand new self powered vacuum chamber suitable for altimeter testing. Durability? Time will tell.

This is going to seriously damage the market for high priced vacuum chambers that are used in applications where specs and approvals aren't crucial and which don't need super low vacuums. I think this may have other uses like getting bubbles out of adhesives, dessication etc. Any other ideas?

Tried bypassing the internal limit switch and the pump stalls out at about 10K. Still, an AMAZING SMOKING deal for $20, and 10K is still useful for testing altimeters. Might try upping the input voltage to see if I can push the pump up to 12-14K at the risk of frying the motor. The unit can run on internal D cells or the wall adaptor. Actually my chamber pumps faster on the D cells, probably because they can deliver more current before the voltage sags in compasion to the small AC adaptor. Vacuum seal is pretty darn good. Takes days to go from 6.5K to sea level when you pump it down, remove power and leave it.


(This post was edited by 377 on Feb 25, 2008, 10:24 AM)



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