Fun google tip: Type "25 inches of mercury in Pa" in Google search (or your Google toolbar) and it will tell you the answer. I use Google now for my calculator whenever I'm at a computer. BTW, 84.6 kPa corresponds to about 36 kft ASL.

My vacuum pump pulls to 25" Hg... don't know what that corresponds to altitude-wise or in millibars or whatever, but it sure can pull v-bagging down tight on a lay-up.

Warren

All other things being eqaul 1" is about 1000 feet(at our altitude anyway), give or take. Climb into an airplane at Vance brand and you will see the manifold pressure gauge sitting at 24.5-25 depending on the weather of coarse. 29.9 - 24.5 = 5.4
5400 feet. Not perfect but close. The runway down there sits at 5050.

Scott, a micron is a very small moron, or a millionth of a meter.

Never thought you were the name calling type 😀

Well, my vacuum pump really sucks after all. In a good way. It turned out that one of its fittings was loose, so once I fixed that, it really pulled it down hard. It inverted the lid of the rubbermaid container I was playing with at about 36,000 feet equivalent which opened the edge seal. Then I tried it again with a spacer to keep the lid from getting too deformed, and it ended up shattering the rubber-edged, see-thru lid. Yikes! Just before it went, the mechanical pressure gage on the pump was reading 21" of mercury, which (since we only have about 24" of Hg to start with) means it had about 60kft equivalent.

The larger altitude chamber I've been using for the calibrations will clearly need to be beefed up. It's about a foot on a side, with 3/4" plywood walls and a see-through lid. But 10 psi * 144 sq inches = 1400 lbs. Hmmm.

Well, my vacuum pump really sucks after all. In a good way. It turned out that one of its fittings was loose, so once I fixed that, it really pulled it down hard. It inverted the lid of the rubbermaid container I was playing with at about 36,000 feet equivalent which opened the edge seal. Then I tried it again with a spacer to keep the lid from getting too deformed, and it ended up shattering the rubber-edged, see-thru lid. Yikes! Just before it went, the mechanical pressure gage on the pump was reading 21" of mercury, which (since we only have about 24" of Hg to start with) means it had about 60kft equivalent.

The larger altitude chamber I've been using for the calibrations will clearly need to be beefed up. It's about a foot on a side, with 3/4" plywood walls and a see-through lid. But 10 psi * 144 sq inches = 1400 lbs. Hmmm.

I think I might have vacume chamber ENVY!!!!!!!!!!!!
I might have to get some of that lexan and a new pump!!!
Adrian your vacume setup SUCKS! 😉

Scott e

Well, my vacuum pump really sucks after all. In a good way. It turned out that one of its fittings was loose, so once I fixed that, it really pulled it down hard. It inverted the lid of the rubbermaid container I was playing with at about 36,000 feet equivalent which opened the edge seal. Then I tried it again with a spacer to keep the lid from getting too deformed, and it ended up shattering the rubber-edged, see-thru lid. Yikes! Just before it went, the mechanical pressure gage on the pump was reading 21" of mercury, which (since we only have about 24" of Hg to start with) means it had about 60kft equivalent.

The larger altitude chamber I've been using for the calibrations will clearly need to be beefed up. It's about a foot on a side, with 3/4" plywood walls and a see-through lid. But 10 psi * 144 sq inches = 1400 lbs. Hmmm.

Adrian

Id loan you my altimeter to check it, But you would break it! 🙁 It wasnt design for the Stratosphere!

I'd especially break it if my chamber implodes. 🙄 But it looks like you were doing just fine testing your altimeter in your own chamber.

A decent absolute pressure gauge and relief valve on your vacuum pump can adjust things to a pretty fine degree if you've got the right relief valve. You can easily, as I'm sure you know, compute the pressure altitude from the difference between off and full on and at whatever relief valve setting. Not what I would call a calibrated altitude, but definitely a viable number - especially if you cross-check with GPS or something.