# Anyone know about vacuum rating?

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I've dug around for quite a while, and although I find all sorts of "comforting" diagonal data about fall heights, column separation, etc, I cannot find a stated vacuum rating for ASTM D2729 pipe (4").

I'm getting ready to re-do a poorly-designed vacuum hold-down system for a ShopSabre 4896 that has only ONE 2" pipe to each half of the table, even though the pump has a 4" inlet!(duh!)

4" water pipe (sch 20-40-80) is slightly too large to fit in the space provided, but 4" ASTM-D2729 sewer pipe will fit. We're only talking 11" of vacuum (or -5.4psi). But I want some margin of safety, and can't find a figure anywhere.

Anyone know?

Thanks, Lloyd

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Lloyd, 2" + 2" = 4". What's your problem? :)

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2 2 inch pipes have an area of 6.28 sq inches. 1 4 inch pipe has an area of 12.56 inches.
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Tim Wescott fired this volley in news:cb- snipped-for-privacy@giganews.com:

Yeah...that's what they thought, too! Lloyd

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unk fired this volley in news:mbr5cj\$dpt\$1 @speranza.aioe.org:

Yes, he knew that; hence the smiley on the end!

Lloyd

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I don't know. d8-)

However, here a few formulas, if you want to trust your calculations. Start with the fact that 4" ASTM-D2729 sewer pipe has a wall thickness (min.) of 0.075".

(click on "product spec")

... for calculating the internal pressure it will take. Then there is a table lower on the page that relates max. external pressure to the max. internal pressure -- for schedule 80 pipe.

My question would be what kind of relationship there is between the internal versus external pressure tolerance for much thinner pipe. There probably is some aspect of the Euler buckling formula at work, but I have no clue about what that would be.

If it were me, I'd build it, stand back, and try it. Crumpling is a lot better than exploding.

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

Yeah.... I'm out to the hardware tomorrow for some end caps and a fitting to hook my HVAC pump up to it. I figure I'll gradually reduce the pressure inside until it buckles (or doesn't!). If it will take -

10psi, I'll be pretty comfortable with it.

It will naturally be stronger in compression (vacuum) than in tension (pressure).

Lloyd

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Except for buckling. It could crumple long before it reaches compressive yield strength.

Calculating buckling is black magic. When you take a basic statics course, the instructor sizes you up and decides whether he/she should even tell you about it, aside from the basic column formula. I took statics in a technology class (no calculus) rather than an engineering class, so I never got into it until long after I was out of school.

Be glad we don't have to calculate it.

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How about two 3" water pipes? 18 > 16. Try to avoid sharp corners.

You could cap a piece, pull a good vacuum and drop typical weights for that site on it, to find its impact resistance which may not be the same as its collapse rating under uniformly distributed external pressure, as from ground water.

-jsw

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That depends very much on the wall thickess. A soda bottle can hold over 100 PSI (200?) but collapses if you put hot water in it and let it cool.

-jsw

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"Test plugs" don't have to be glued on or cut off and discarded afterwards. My ISP is slow tonight and not returning images, but I remember using a type with a garden hose fitting to fill the newly installed drain plumbing until water ran out the roof stack, to check for leaks before installing the sinks and toilets.

-jsw

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"Jim Wilkins" fired this volley in news:mbrdps\$cem \$ snipped-for-privacy@dont-email.me:

I have (literally) a shelf-full of them. But all mine are for "scheduled" (SDR) pipe. I don't even know if they make them to fit the thinwalled sewer drain pipe. I'll check. but since I need only make one test, and because I can selectively save at lease one of the caps by leaving it on the piece... It won't cost me more than a couple of bucks.

Lloyd

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They do make bushings to use standard fittings on that thin wall drain pipe .

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Wouldn't the area of a pipe depend on it's length? It seems like a long pipe would cover a lot more area than a short one.

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We're talking cross section , not volume . Double the diameter and you quadruple the cross section .

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Is that similar to circular mills? For example, 2 24 gage wires twisted together will carry the same maximum current as 1 21 gage.

technomaNge

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"Terry Coombs" fired this volley in news:mbrlla\$mlr\$ snipped-for-privacy@dont-email.me:

Yep, and I'm counting on that so as not to throw away the parts of the ShopSabre plumbing that are (at the least) just adequate.

I plan to later 'plenum' the entire underside of the table, rather than using a system of collector pipes, and to also 'remote' the pump to just outside the room, for noise control. (a 20HP regenerative blower makes a racket!)

That wouldn't work for someone who did smaller work, but everything we do on the machine is with full 4x8 sheets of stock (yeah, I know, 'famous last words').

It only breaks into four zones now, so just keeping 3/4 of a sheet of stock cut into 1/4-sheet pieces would do the 'zoning' as well as the valve system it has now.

Lloyd

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Tim Wescott fired this volley in news: snipped-for-privacy@giganews.com:

???

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technomaNge fired this volley in news:mbrmo8\$pa3\$1 @dont-email.me:

Same concept. Only, ShopSabre used the logic thus:

"If it takes a 12-gauge wire to go 12 feet, then I should be able to run

36 feet with only 36 gauge wire! We'll save LOTS of money!"

Lloyd

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Two 3" pipes are slightly larger than one 4" pipe, so you could just make the pipe to each half 3" Sch. 20, 40 or 80 and run to a 4" (via Tee, Wyes, reducers etc in the smoothest transition manner possible) at the pump/bower. Should be effective and means not trusting SDR to do too much, which is usually a good idea.

If committed to using 4" sewer pipe, being a practical git and an old vacuum hand, I'd rig up a test section and suck it down to 30" to see if it collapsed or not. Use a regular roughing pump that can just pull that without a sweat, not your blower/pump which probably can't. Leave it for a good long while. Barring some sort of kink, defect, etc I would not be too surprised if it didn't collapse. If it did, I'd pay attention to when that happened (if during pump-down) and try another piece at an inch or two less, until it didn't, to get a general idea of where it usually failed. A trap/screen on the pump input would be wise for this testing, as might a wire cage around the test pipe in case of shrapnel leaving.

On the third hand this is the ugly cousin of using PVC for compressed air; but I guess most of the shrapnel would end up in the pump/blower if/when it failed.

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