Test chamber

[Rex R]

wanted to test an altimeter (or two) so I made a test chamber...I got fancy could have saved some time and simply drilled a 1/16" hole in the lid . used a canister vac to 'pull' an altitude(about 3400'). did just for fun 'send' my alt1 to 14k .
rex

 

[cerving]

Get an automotive brake vacuum puller, and you'll be able to get to 14K. You may need to get a slightly smaller jar, however.

 

[fyrwrxz]

Looks easier to use than a juice box and sippy straw-+1!

 

[cwbullet]

It will work. I use my Foodsaver.

 

[Onebadhawk]

It will work. I use my Foodsaver.

That is an excellent idea.....

Will you please explain this to the Mrs........

Teddy

 

[RocketflierVB]

You can't use a hand pump to pull a vacuum, I quickly found out that as soon as you stop squeezing the altimeter thinks it is at apogee...you'll need to have some thing that will pull a constant (slow) vacuum. I have made a chamber with my vacuum pump but I need to find a chart that will cross reference a vacuum to an altitude...I am afraid of pulling to much and damaging the altimeter...

 

[Rex R]

in my case I just wanted to see if the alt still worked and for that all I needed was an 'apogee' higher than 500'. the vacuum cleaner* was all I needed . also discovered that the mach delay works.
rex
*for that matter one could just suck on the hose...but you'll get a nasty taste when the pyrogen lights .

 

[accpool]

You can't use a hand pump to pull a vacuum, I quickly found out that as soon as you stop squeezing the altimeter thinks it is at apogee...you'll need to have some thing that will pull a constant (slow) vacuum. I have made a chamber with my vacuum pump but I need to find a chart that will cross reference a vacuum to an altitude...I am afraid of pulling to much and damaging the altimeter...

please explain why you can't use a hand vacuum pump. i am not doubting just want to understand.

 

[Rex R]

you can for something like the altimeter1/2, but for testing a dual deploy alt it will have an apogee event the 1st time the pressure stops falling.
realistically the highest altitude you can simulate is around 60-70k https://usatoday30.usatoday.com/weather/wstdatmo.htm#us
rex

 

[awseiger]

I was considering using one of the pumps used to inflate things like pool floaters and airbeds. They usually have a suction side that I suet would get me to the 2000ft range. If not, I have access to a real-deal vacuum pump.

I want to get in the habit of testing my altimeters, in the bays, with live charges (outside the air chamber, obviously).

I'm thinking of a clear PVC chamber. Anybody have any other suggestions for a clear tube?

 

[Target]

So a hand pump will not work?

https://www.harborfreight.com/catalogsearch/result?q=brake+pump

I was consideing getting this from harbor.

 

[Rex R]

only if you have a very small chamber volume.
U.S. Plastic corp. lists clear pvc pipe...3" sch 40 is approx. $17 per foot (before shipping). if you need transparent fittings, well the price is much higher. standard fittings can be used if you don't need the entire chamber transparent. fortunately running binding posts through plastic pipe is fairly easy(the spud launchers do it all the time ).
Rex

 

[Rex R]

one could use a hand pump to pump down a 'storage vessel' from which you would 'bleed' the air from the test chamber, but that requires twice the number of connections (that will probably leak) and at least one valve (vacuum rated). not to mention that such a setup has limited use around the house .
rex

 

[Target]

Rex
I have small adept 22's and was hoping to use a pimento jar. I believe the volume inside the jar will be small since I plan to use the "shorter" jar. What do you think? Will is work? Thanks.

 

[Rex R]

depends on how much air the pump can move in one stroke compared to your chamber. unless you have a need for a high altitude, I'd suggest a vacuum cleaner. I note the folks at PerfectFlite recommend the vacuum cleaner method for testing their altimeters and ground testing deployment charges.
rex

 

[bobkrech]

You can't use a hand pump to pull a vacuum, I quickly found out that as soon as you stop squeezing the altimeter thinks it is at apogee...you'll need to have some thing that will pull a constant (slow) vacuum. I have made a chamber with my vacuum pump but I need to find a chart that will cross reference a vacuum to an altitude...I am afraid of pulling to much and damaging the altimeter...

The best atmospheric calculator is here. https://www.aerospaceweb.org/design/scripts/atmosphere/

You can't hurt the altimeter pressure by pulling a vacuum on it. That's what it's designed for. You can damage it if you pressurize it substantiallly above atmospheric pressure however. That level is about 2 atmospheres.

A way to simulate a flight to a specific altitude is to have 2 chamber of different volumea connected by a valve. If you pump out the larger one to eliminate most or all of the air, then open the valve, you will simulate a launch to an altitude equivalent to the equilibrium pressure when the valve is fully open. If you then vent the large chamber, you will pressurize the smaller chamber at a slower rate than you pumped it out simulating descent.

The math is pretty simply. The volume of the test chamber is V1 and the vacuum ballast chamber is V2, and the pressures in chambers is P1 and P2, and when equalized Pe which is the atmospheric pressure at the desired altitude.

Pe = (P1 x V1 + P2 x V2)/(V1+V2).

To equilibrate a specific pressure Pe equivalent to your desired apogee altitude, you need to pump out V2 to a pressure

P2 = [Pe x (V1 + V2) - (P1 x V1)]/V2

To figure out the volumes of the chambers you need a digital scale that measures in grams and has a capacity of several kilograms. A liter of water = 1000 cc or ml and weighs 1 kilogram. If you put an empty jar on the scale and weigh it, record the weight, and then tare out the weight of the bottle. Fill the jar with water with water and record the weight of the water added to fill the jar. The weight of the water in grams is the volume of the jar in cubic centimeters. to make sure you have not exceeded the capacity of the scale add up the tare weight of the jar and the weight of the water and make sure it is below the maximum capacity of the scale.

Bob

 

[BEAR]

For my small vacuum pump (?) for my test chamber, I went to the vet supply and got the biggest syringe I could get. Something for use on horses and cows. I got a big honken needle, almost an 1/8" in diameter. I drilled a hole in the top of a pint size mason jar lid, glued in a piece of brass tub, and ran a tight fitting piece of rubber hose over the brass tube. When I want to draw a vacuum, I wet the end of the needle, then slide it into the hose and start pulling on the piston. If I want to hold the vacuum, I get a pair of surplus surgical forceps and clamp it off. Crude but effective. I have not taken the time to build a nice one with a vacuum guage and pump, but I might some day when the need arises. For testing the psuedo ejection charges, little Christmas lights work fine and can easily be seen or filmed for replay.

 

[Target]

this may be of interest.....the issue here is the pump can not be seen.

https://www.youtube.com/watch?v=b2fR2jYYzFM

 

[Target]

https://www.youtube.com/watch?v=BpOUL4q2JFY

the pump is a hand held auto pump.

 

[tightwad]

I also use a 100 cc syringe and a small mason jar to test my altimeters. It works great for my usage, but it isn't very pretty.