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  1. #1
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    Portable Vacuum Chamber for Altimeter Testing

    This past winter while sucking on a piece of rubber tubing, and trying to keep the other end on the baro sensor to test a altimeter, i knew there had to be a better way. And then it hit me, a small portable vacuum chamber, would be just the ticket. Only problem was i had never seen one for sale, or the plans for one. No problem, i would just design and build one. Of course it never turns out to be as easy as one thinks, but overall it was not too bad.

    The first thing i did was to look around the shop and start gathering things up that i would need. A small piece of plywood for the base, a 12 volt tire inflator, on which i would reverse the fittings and turn into a vacuum pump, a small lead acid battery for power, a piece of pvc pipe for the chamber, a piece of lexan for the top, a couple of valves, some brass tubing and hose, a couple of terminal strips and wire, and a small case to put it all in.

    This was going to be easy, i had everything that i needed, and did not spend a dime. Sure. First thing i did was to tackle the pump. Long story short, the tire inflator did not work. Not a problem, i had another 12 volt tire inflator that i would use. After another hour or two, i now had two tire inflators that would never inflate another tire, but still no vacuum pump. Well i was sure that i could find what i needed on ebay. Turns out that i did, a used, small 12 volt vacuum pump for only $4.95, but wait, shipping was $15.00. After looking on ebay every day for a week, and finding nothing else, i went and ordered the pump. If it did what i wanted, i was ok spending $20 on it. Turns out it works great. Next i built the vacuum chamber. I cut a 7 inch long, piece of 2 inch pvc tubing length wise a little above center, added a couple of end caps and a top of lexan, drilled a hole in each end cap for fittings, addded a rubber seal on top, and drilled six holes for the connection wires. It looked good and seemed to work fine.


    At this point i hooked the pump up, put a altimeter into the chamber and turned it on. It did not work. Turns out that the pump does not pull a vacuum smoothly and evenly, it sort of work in jerks and drove the altimeter insane. So, a storage chamber for the vacuum would be needed. I had some 4 inch pvc and a couple of end caps, so i cut a piece that would fit in my case, drilled and tapped one end cap for fittings and cemented it together. Another quick test showed that this was the answer.

    At this point i was ready to assemble it. I cut the plywood to fit my case and stained it. Painted the storage chamber blue, with some left over spray paint and mounted it, Built a hold down for the battery, and installed a on-off switch on the pump and installed them. Added some hold downs for the vacuum chamber, installed the terminal blocks, and hooked them to the wires coming from the chamber. Connected the pump, storage tank and vacuum chamber together with brass tubing and hose, installing the valves where needed. Added some labels to the terminal strips and i was done.


    It works great. In the end, the only out of pocket cost was $20 for the pump. If one were to purchase all the parts new, i think it could be built for $80-$100. I added a few pictures and a short video of it in use. All comments and ideas on how to make it better are welcome. If someone decides to build one, please feel free to pm me for any information or help you might need.

    Mike Corbett




    http://www.youtube.com/watch?v=RrlxuApQND4
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  2. #2
    Interesting that you need to have a storage tank to hold the nothing that you're using.

    Cool tool, and nice execution.

  3. #3
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    troj is offline Wielder Of the Skillet Of Harsh Discipline, Potentate of Perilous Pans TRF_ADMIN.png
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    Nice idea. I'll admit, I just use a mason jar with a piece of aquarium airline poking through the lid -- drop in altimeter, screw on lid, and suck out the air.

    I do like the idea of something a bit more controlled, especially if it will let you hold the vaccuum at a specific point.

    Why such a large manifold to balance out the pump? Or was that a case of "I have some pipe of this size laying around"?

    I may have to build one of these for myself....

    -Kevin

  4. #4
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    Hmm

    That is awesome. I think this would be great as a build thread with part list. Can you post a list of your parts?
    -----------------------
    Chuck Haislip
    NAR/Tripoli Level 3 Prefect ICBM - TRA #60

    Level 1 - LOC Minie Magg; Level 2 - PR Broken Arrow;
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    Ns for Year: 2250 but back in the USA. Builds starting today!!!!
    My rockets usually fly naked. If they survive, they earn their paint.

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  5. #5
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    Portable Vacuum Chamber for Altimeter Testing

    I used a quart canning jar with LEDs plus series resistors for the e-matches. That let me see the lights flashing. Maybe you could use a glass jar for the pressure chamber in your design so any flashing lights on the altimeter board would be visible.
    Larry

  6. #6
    Very nice build. I like that you fit it into a case.

    The pvc tank is like the storage tank on an air compressor, just opposite.

  7. #7
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    Quote Originally Posted by catman001 View Post
    Only problem was i had never seen one for sale, or the plans for one.

    ]

    Adept has been selling simple ones for years. Uses a syringe to pull vacuum.

    http://www.adeptrocketry.com/vacuum.htm

    But that's a very nice unit ya built .
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    Jim Hendricksen
    L-3 Tripoli 9693
    ICBM, Orangeburg SC - QCRS ,Princeton ILL - MDRA , Price Maryland - Woosh, Bong Wisconsin- ROCC, Charlotte NC
    "Made" member of Chicago & Carolina Rocket Mafia
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  8. #8
    Quote Originally Posted by blackjack2564 View Post
    Adept has been selling simple ones for years. Uses a syringe to pull vacuum.

    http://www.adeptrocketry.com/vacuum.htm

    But that's a very nice unit ya built .
    I made essentially that exactly thing out of a similar wash bottle I got from American Science and Surplus plus a length of rubber tubing (same source). That's what I used to test MAWD telemetry gizmos. Works just fine.

  9. #9
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    Hi guys, ill try to answer some questions and comments.


    Why such a large manifold to balance out the pump? Or was that a case of "I have some pipe of this size laying around"?
    My thought process was that when i opened the valve between the storage tank/manifold and the vacuum chamber, the vacuum would stabilize between the two at a lower level than the vacuum in just the storage tank. I wanted as large of a storage tank that would still fit in the case, and the smallest vacuum chamber that i could put my largest altimeter into. If the storage tank and the vacuum chamber were the same size, then the maximum vacuum that i could pull in the chamber would be 1/2 of the maximum vacuum in the storage tank. The pump, while it works great, is just a small ,battery operated device, that pulls about 18 inches of vacuum. If i cut that in half, then the chamber would only pull 9 inches of vacuum. While im not sure off the top of my head, i think 9" inches of vacuum would only indicate a altitude of about 10,000 feet. I wanted to sim as high of a altitude as i could, thus the large storage tank. Hope that makes sense. And yes, 4 inch pvc is what i found in the shop. Turns out that with the 1/4 inch plywood base and the height of the end caps, it fits in the case, with about 1/2 inch to spare. Just lucky, but a perfect fit.


    That is awesome. I think this would be great as a build thread with parts list. Can you post a list of your parts?

    Not sure about a build thread, but i could come up with a parts list. It will take me a few days to get to it, and to make the plumbing a bit more simple that what i have. I used whatever i had on hand, and have couplers and adaptors that would not be needed if one were going to buy the parts.


    Adept has been selling simple ones for years. Uses a syringe to pull vacuum.

    I have a couple of Adept altimeters, and have seen the chamber on their web site. Looks like it works fine. Just never got around to buying one. I did use the glass jar and a piece of tubing, until i dropped the jar. Thats why i was just using tubing, it was all i had left. LOL



    Mike

  10. #10
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    Vacuum

    What sort of vacuum pump is that?
    -----------------------
    Chuck Haislip
    NAR/Tripoli Level 3 Prefect ICBM - TRA #60

    Level 1 - LOC Minie Magg; Level 2 - PR Broken Arrow;
    Level 3 - 10 inch Nike Smoke
    Ns for Year: 2250 but back in the USA. Builds starting today!!!!
    My rockets usually fly naked. If they survive, they earn their paint.

    Come fly with ROSCO or ICBM in Orangeburg SC => http://rocketrysouthcarolina.com/ind...erid=$1-ChuckH

  11. #11
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    The pump was made by Thomas. They along with Gast seem to have a good name in the vacuum pump business. I could not find a part number, but i believe it was used in a portable blood pressure monitor. It has two inlets/outlets, and can be used as either a pressure or vacuum pump. I did measure the current draw at about 300 milliamps, so at only about 3.5 watts it is a low power device. When i was looking for pumps, i found quite a few 12v pumps that were used for air assisted brake systems, but they were a lot more expensive, quite a bit larger, and had a current draw in the 6-10 amp range.

    Mike

  12. #12
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    Test container

    The test chamber or container that you put the altimeter in, what is made of? PVC?

    How did you make a seal?

    Thanks for the clarification.
    -----------------------
    Chuck Haislip
    NAR/Tripoli Level 3 Prefect ICBM - TRA #60

    Level 1 - LOC Minie Magg; Level 2 - PR Broken Arrow;
    Level 3 - 10 inch Nike Smoke
    Ns for Year: 2250 but back in the USA. Builds starting today!!!!
    My rockets usually fly naked. If they survive, they earn their paint.

    Come fly with ROSCO or ICBM in Orangeburg SC => http://rocketrysouthcarolina.com/ind...erid=$1-ChuckH

  13. #13
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    CW, yes the chamber is made from 2 inch pvc pipe. The ends and top of the chamber were cut from from a piece of 1/4 inch Lexan. I added a few more pictures that show a little more detail. If you look close you will see that 5 holes were drilled in each end piece and attached to the ends of the pvc pipe, with small 2/56 sheet metal screws. I coated the ends of the pipe with clear silicon chalk, before attaching the lexan end pieces. Once i had the end pieces attached, i just placed a piece of sand paper on my table saw (flat surface), turned the chamber upside down and sanded until the end pieces and sides of the pvc were flat. The blue seal that you see on top of the chamber is just some tool box drawer liner, that i think i got at sears a while back. Any sort of gasket material that the auto parts stores sell should work fine. Again i just used clear silicon to attach the seal. The wires that pass into the chamber are also sealed with silicon.

    I added a picture of the end of the storage tank, so you can get a idea of how i plumbed the tank to the pump. The small clear line going from the compression fitting to the pump, is just a piece of tubing left over from a ice maker kit that i installed on a fridge.

    Any more questions, just ask.


    Mike
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  14. #14
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    Nice work.

    I built something similar that I use for vac-bagging and I used test caps for the ends of the PVC pipe. Test caps are used by plumbers to temporarily seal off the plumbing in a house when pressure testing a new system. The test caps are sturdy enough, in my case, to not break when put under a full vacuum.

  15. #15
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    A shop vac pulls the equivalent of about 3000 feet.
    Adrian Adamson
    Featherweight Altimeters LLC
    www.featherweightaltimeters.com

  16. #16
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    Great system, Mike. Well done.

  17. #17
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    Chamber

    Cool chambers!

    The cheapest one I've used is a square plastic container like you get from Costco which held peanuts (I think). Use a sharp knife to bore a tiny hole in one corner. Toss the altimeters in (it will hold about 120 AltimeterOnes), close the lid firmly, suck on the small hole. Good for about 3K feet. Useful if you trust one altimeter and want to test another.

    The most expensive one I made for AltimeterOne development. It uses a special high-tech vacuum pump from Gast that is good to about 30,000 feet of pressure altitude. By the way, pumping the last molecules from a most empty chamber is hard, it turns out.

    The chamber has a super-accurate pressure sensor (costs hundreds of dollars for just the sensor) and a high speed 24-bit analog-to-digital converter from Hungary that collects data and interfaces to a computer. The A2D converter costs as much as the rest of the system put together, by the way.

    There are two vacuum chambers, connected via a valve to a smaller testing chamber. The testing chamber has big twist knobs and one whole end that can be removed to make it more convenient to open and to place altimeters into. All of the chambers are 1/4 thick acrylic, with special rubber gaskets and sealant on everything.

    In use, you pump the vacuum chambers as low as you have patience for (it takes a while), you load the testing chamber with units and seal it up, then you turn the valve to lower the pressure in the testing chamber as slowly or quickly as you like. Meanwhile, the computer records the entire history many times a second.

    Here's a photo (the electrical cord is tossed on top, and two of the knobs are removed):


  18. #18
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    Thumbs up Cheap fix

    Having a similar problem, I recently made a very cheap and very functional vacuum bottle. Like most others I was using a jug, jar or bottle and straw. What I eventually came up with works great!
    Take two empty plastic liter soda bottles in your choice of size. drill a hole in the cap for your tube to pass through. Cut the top off one bottle in a funnel shape then cut a large opening - slightly smaller than the funnel cut in the top of the second bottle. The "funnel" will have the cap and tubing attached. Drop your electronics into the container bottle and just set the "funnel" over the opening. the tolerance are so close that absolutely no air will escape. Cheap,easy and quick to throw together.
    Blackbird Rocket Group
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  19. #19
    Quote Originally Posted by catman001 View Post
    CW, yes the chamber is made from 2 inch pvc pipe. The ends and top of the chamber were cut from from a piece of 1/4 inch Lexan. I added a few more pictures that show a little more detail. If you look close you will see that 5 holes were drilled in each end piece and attached to the ends of the pvc pipe, with small 2/56 sheet metal screws. I coated the ends of the pipe with clear silicon chalk, before attaching the lexan end pieces. Once i had the end pieces attached, i just placed a piece of sand paper on my table saw (flat surface), turned the chamber upside down and sanded until the end pieces and sides of the pvc were flat. The blue seal that you see on top of the chamber is just some tool box drawer liner, that i think i got at sears a while back. Any sort of gasket material that the auto parts stores sell should work fine. Again i just used clear silicon to attach the seal. The wires that pass into the chamber are also sealed with silicon.

    I added a picture of the end of the storage tank, so you can get a idea of how i plumbed the tank to the pump. The small clear line going from the compression fitting to the pump, is just a piece of tubing left over from a ice maker kit that i installed on a fridge.

    Any more questions, just ask.


    Mike
    I love the attention to detail and craftsmanship - well done sir. Functional and a piece of artwork in my opinion.
    Cheers!

    -Serpico

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  20. #20
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    Quote Originally Posted by John Beans View Post
    Cool chambers!

    The most expensive one I made for AltimeterOne development. It uses a special high-tech vacuum pump from Gast that is good to about 30,000 feet of pressure altitude. By the way, pumping the last molecules from a most empty chamber is hard, it turns out.
    John,

    For a long time I was getting by with a similar pump, only able to test to about 40,000 feet equivalent. After Jim Jarvis' ill-fated flight to 100,000 feet last fall, I got an air conditioning evacuation pump (~180,000 feet equivalent) from Harbor Freight for under $100. I still have butt bruises from kicking myself for not getting it sooner. It's the oil-filled type, but it works great if you want a harder vacuum than you can get with a Gast-type pump.
    Adrian Adamson
    Featherweight Altimeters LLC
    www.featherweightaltimeters.com

  21. #21
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    Quote Originally Posted by Adrian A View Post
    John,

    For a long time I was getting by with a similar pump, only able to test to about 40,000 feet equivalent. After Jim Jarvis' ill-fated flight to 100,000 feet last fall, I got an air conditioning evacuation pump (~180,000 feet equivalent) from Harbor Freight for under $100. I still have butt bruises from kicking myself for not getting it sooner. It's the oil-filled type, but it works great if you want a harder vacuum than you can get with a Gast-type pump.
    Nice tip, Adrian. Thanks!

  22. #22
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    I use something similar for vacu-bagging. My pump is an HVAC pump that I bought on E-Bay for about $100. This model is rated at 5cfm which works well for vac-bagging, though you can get a cheaper pump if you don't need that much performance.

    The one glitch with these pumps is that they have an Acme fitting that is used in the HVAC industry and it's a hassle to find a Acme-to-NPT fitting so that you can use standard pipe fittings in your setup.

    Also, the oil used in these sorts of pumps is usually a vegetable oil and is much cheaper online versus a local supply shop. I got pretty much ripped off by a supply shop that only sold wholesale and did me a 'favor' by selling me the oil and the fitting.
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  23. #23
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    Quote Originally Posted by Pat_B View Post
    I use something similar for vacu-bagging. My pump is an HVAC pump that I bought on E-Bay for about $100. This model is rated at 5cfm which works well for vac-bagging, though you can get a cheaper pump if you don't need that much performance.

    The one glitch with these pumps is that they have an Acme fitting that is used in the HVAC industry and it's a hassle to find a Acme-to-NPT fitting so that you can use standard pipe fittings in your setup.

    Also, the oil used in these sorts of pumps is usually a vegetable oil and is much cheaper online versus a local supply shop. I got pretty much ripped off by a supply shop that only sold wholesale and did me a 'favor' by selling me the oil and the fitting.
    I've never seen a high vacuum pump use vegetable oil. All of mine use highly refined natural or synthetic oils which are expensive.

    A good commercial substitute for "conventional" vacuum pump oil is Mobil 1. It has a very low vapor pressure and is available at your local auto supply store for around $6 per quart. We had a $30K commercial ppb level NOX analyzer with a straight from the factory high vacuum pump that used plain old Mobil 1. Ran for years continuously without having to change the oil.

    Bob

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