Anyone know about vacuum rating?

Indistinguishable on the relevant dial gauge...

Also perfectly achievable on any day with a high pressure system in place, at least in Florida, where 345 feet is as far above sea level as you can get. At about the time you wrote this, 30.19 inches at KOBE...a "standard" atmosphere is an agreed upon average, not something the actual atmosphere has to comply with. Might be a tad more impossible in Denver.

I was being shown around a local workshop making high end souvenir models and one of the workers said how the vacuum degassing chamber could pull 2 atmospheres, I just looked at my mate as he looked at me and we both knew it wasn't worth commenting on so let it pass. Theoretically possible if you have a hyperbaric chamber for the initial mixing but unlikely.

I'm looking to use an old compressor tank, or half of it, as a vacuum degassing chamber and have pulled about 0.95 atm on it with no problem but it is a reasonably heavy wall tank. Comments online I noted say that failures of vacuum chambers are rarely spectacular when they collapse but then the comments were about ductile materials such as steel which just crumple.

David Billington fired this volley in news:mbtho2$1as$1 @dont-email.me:

And so does 'fresh' PVC. I wouldn't bet on the results with 10-year-old stuff the plasticizers had gassed out of..

LLoyd

Well, 20 torr is only about 0.4 psi absolute. So the difference is insignificant.

Ed Huntress fired this volley in news: snipped-for-privacy@4ax.com:

Apparently, you've never manned a firefighting rig!

That 'overshoot' I was talking about can go up to 8 psi under the right circumstances.

Lloyd

Ed Huntress fired this volley in news: snipped-for-privacy@4ax.com:

Oh... you you missed the most basic point. Yep... 20 torr IS about .4 psi, absolute.... figure that FROM 14.7-odd psi atmospheric.

Lloyd

Well, that's true. The closest I ever came was fixing a pump motor for the volunteers in my old town, 40 years ago.

We're miscommunicating. The pressure can only drop an addition 0.4 psi from the pressure with fully-water-saturated "vacuum." That's all the "overshoot" that's physically possible.

Let's try this again. When the water column separates, the water vapor pressure would allow the absolute pressure to drop to 0.4 psi. That's

14.3 psi LESS than atmospheric.

When a column separates, the gas pressure in that bubble consists only of the water-vapor pressure (or the vapor pressure of whatever liquid was in there.)

Are we on the same page?

Ed Huntress fired this volley in news: snipped-for-privacy@4ax.com:

Ok... I understand that is all the overshoot possible, but the absolute pressure within that vertical pipe can be drawn down by the falling water TO 0.4 psi (at 'room temperature' theoretically). That's pretty close to

14-1/4 psi of vacuum relative to atmospheric.

LLoyd

Ed Huntress fired this volley in news: snipped-for-privacy@4ax.com:

Yes, exactly. What you just stated was precisely what I was trying to express... that the vacuum within the pipe would well-exceed that necessary to completely collapse it (sans surrounding 'soil support').

Somehow I mistook you to mean that the pressure could only _drop_ by 20 torr... sorry.

LLoyd

So far so good. How does 'five stories' relate to that?

"Lloyd E. Sponenburgh" wrote in news:XnsA442AB59DF12Clloydspmindspringcom@216.168.4.170:

Lloyd, I don't know of an official vacuum rating for this pipe, but I do have first-hand experience using D2729 sewer pipe in vacuum applications. A couple of years ago, I built the system shown here

as the vacuum engine for a woodworking veneer press, using D2729 pipe for the twin vacuum chambers. I've repeatedly cycled this system to 21" of vacuum, including a couple of pressings a year ago where it held that vacuum for four hours at a time.

And I've had no problems at all -- which would suggest that you probably have about a 2x margin of safety.

Doug Miller fired this volley in news:XnsA443B36457507dougmilmaccom@213.239.209.88:

Doug, my sample collapsed at about 11". I'm sure vendors' products vary.

Lloyd

What's the diameter of Doug's pipe? Smaller diameters could handle a lot more vacuum.

Ed Huntress fired this volley in news: snipped-for-privacy@4ax.com:

Yup. L

"Lloyd E. Sponenburgh" wrote in news:XnsA443BF2B74EB6lloydspmindspringcom@216.168.4.170:

4", same as Lloyd's. Mine is in sections only about 15" long, though, which probably accounts for the difference in our results.

That certainly would allow more vacuum than the longer lengths, but the calculations are beyond me.

Doug Miller fired this volley in news:XnsA443C2A7B820Ddougmilmaccom@213.239.209.88:

Probably does, but I needed to test the 8' length I'd need for the collector. Shorter would be better, if I could use it.

LLoyd

That's definitely not something you learn in class -- you get that after you're fending for yourself in industry.

A good engineering education should teach you the basics, and how to learn anything on top of that, but cannot, of necessity, do much of the "on top of that", because it takes decades.