Keeping 3/4" and 1/2" PVC From Sagging.

I am assuming that the PVC is not conveying anything. It is being used as a structural member?

What type of load will it see? 1 lb? 10 lbs? 50 lbs?

How long of a span?

Would spray foam insulation work?

A sketch or picture of what you're trying to build would be helpful. Don't forget to include dimensions.

Concrete might work, but I like the idea of spray foam.

He might need a longer delivery tube to get to the middle of a 10 foot section.

Or maybe just drill some injection holes along the pipe evey foot or two?

Foam is flexible.

You need a material with a high rigidity such as metal, but there is no mention of what the load is, where, over what length, and how much sag is permissable to even begin with a recommended material.

Then it begs the question of why not just use steel or aluminum tubing or rod in the first place and ditch the PVC?

And how much sag is acceptable?

Honestly, assuming we are discussing sag and not buckling, I think anything that does not have a much higher Modulus of Elasticity than the PVC will do very little, a steel rod or pipe, if you can find one to fit, might do the trick.

If it is about buckling, the foam might work.

Plaster of Paris also springs to mind but I prefer the expanding foam better!

Possibly cut narrow strips of 1/8" plywood and insert into pipe. Use foam, RTV or whatever to keep plywood from turning away from vertical. This assumes that the pipe can be clamped stationary.

Stick a wood, aluminum, or steel rod or conduit tube in it. No need to over engineer the obvious.

I was thinking it might be easier and 'rigid enough' (depending on your load) if you could create an I-beam with the PVC, but since the tubing is round, it might be easier to weld 3 tubes together with PVC cement. The tubes would have to be cleaned thoroughly first. I'd think this would be a lot easier than trying to fill a long pipe and ensure there are no air gaps.

Of course, if the thing you are building can't accommodate the extra room, then you might consider glass-fiber reinforced concrete. Fiber glass is cheap, as is a bag of the top-coat type of concrete (the kind without rocks).

Well -outside the PVC tube Aluminium U profile could be used

-but the question if it is design feasible, if yes the rigidity will be superior to any rigid stiffening system - inside the tube !!

use a smaller diameter pvc pipe and side it inside the larger one. it does'nt matter if it's a tight fit. it's best if it is'nt we''ve used this method for years, but it involved sleel pipe.

it should apply to your situation too.

what is the application? like others said just put in a metal pipe in it that just fits, if weight is not a problem you could put in concrete.

There are UHMW PE tubes available that might meet your inferred requirements. Or add a mid-span support. Or Lyn-Door?

I would go with a fairly thin metal tube fitting as snugly as practical inside the PVC. EMT electrical conduit comes to mind, but I don't have a table of diameters handy.

You can't gain on moment of inertia, but the modulus of elasticity of the metal will help. Carbon fiber tube could be even better, but much more costly.

I once used rebar and mortar. It was used for a fish enumeration fence in a stream. Pieces about 4 feet long.

Until we have more details we are blowing smoke.

Lots of commentary, BUT-

First- liquid or foam of almost zero or negative value- add weight and no strength.

Second- Concrete ALMOST same as foam/liquid

Third- BruceFlorida (#7) is best so far

Take #7 and expand- use 2 strips slit and fit together in "X" shape, sized to JUST fit into the tubes. A couple quick squirts of wood glue in the grooves will lock everything into place. No matter what the rotation of the PVC, there will be significant resistance to sag due to combined compression / tension in each of the strips and the friction fit will keep everything aligned.

I think this is better that the thin-wall tube concept that jumped to mind for me (and was mentioned by a few other posts) but this solution is the cheapest and best for the challenge posted- no matter WHAT the span AND the OP has already stated a minimal loading- essentially dead load of the pipes.

I think we've been here before:-

http://cr4.globalspec.com/thread/66957

Thanks to all who replied. Sorry I wasn't so specific. We are trying to build a blind for a welding area, as well as well ventilated area. Trying to cut costs, we have a bunch of PVC laying around and were trying to figure out something. Height was a concern, so we are worried about the sagging. Some of the runs would be longer than 10'. Thanks again.

Well build blinds with tubes also as diagonals !! This reinforcement will do the stiffing

I am not sure I really understand what a blind is, but if you are trying to build something that acts as a visual barrier, why do they have to run horizontally?

Maybe you could run them vertically?

I wish you could give us more information or even a picture or drawing.

I am now guessing (since our OP doesn't want to tell us) a welding screen frame is what he is up to. This sort of thing:

Ye, gods... going cheap on safety equipment like this?

Easy solution here is to just build a set of MODULAR units- each about 3-4 feet wide with 3/4" pipe as horizontal top bar (stiff enough for that span) and use 1/2" (or 3/4", depending on how much you have) for uprights and lower span (a little "sag" here will pull the barrier material tighter.

Pipes usually come in 10 foot lengths, so make each 3 ft 6 in wide (3 each at 3 ft 4 in pipe "beam" plus fittings/column width).

Put extra verticals in as needed, or "weld" two or three together(previously proposed by Usbport) or make a truss out of the pipe.

I would use EMT (electrical metallic tubing) raceway instead of PVC pipe. If you really want to use PVC pipe, perhaps take a look at that "Ballistics Gell" stuff the Myth Busters use all the time. I would imagine it comes in different levels of rigidity.

Bundle them a triangle (3) glue or wrap tight every foot or so ...

I think that a piece of aluminum "U" channel the appropriate size will make the PVC tubing rigid enough for what you are doing. There are companies that make all kinds of extruded aluminum shapes. The ideal shape would be that of a star when looking at the end of the material. It would have been nice of you to put the application in your question so we could determine the factors of strength and rigidity.

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A hand without an arm is a useless tool.

You have proposed a solution..."make it rigid"...what problem are you trying to solve? Length, weight of loads, etc etc would be helpful.

ooops sorry did not see the blind description...

Yeah, I see it now,too. :)

Spend the money, buy the right equipment, that way when something happens to the backwoods blind, there is no liability or gilt.

Some items have safety regulations and rules to them for a reason, don't be cheap with peoples safety!

3/4" PVC is 1.050" diameter. A steel bar 10' long and 1.050" diameter would also sag. You will never get PVC to sag close to the solid steel bar, no matter what you use to fill it with. A solid steel bar the same ID as the PVC is the best you will ever get. You need to tell us what is the maximum sag you can live with, what is the span and what you are hanging from the PVC.

Putting a slight upward bow on the PVC will help minimize the sag, but the ends have to be firmly attached and not allowed to twist.

I had a problem where somebody had used 22mm OD copper pipe as a rail in a wardrobe, and it was sagging. I found some ordinary reinforcing bar from a site I was working on and inserted that. Job done.

Electrical conduit would probably be cheaper than copper and lighter than rebar.

The 22mm copper was already there. I doubt whether electrical conduit on its own would be much stiffer than the copper pipe. Steel pipe 1/2" NB, ~ 21.5mm OD would probably have been as good, but I couldn't get hold of any easily. The weight of the rail is insignificant vs that of the clothes hanging on it.

Take your 3/4" PVC, put a tee at each end and bow it upward just enough to eliminate the sag as shown in the sketch.

Use a T-Piece and add additional vertical struts as necessary to withstand the load without sagging.

e.g. -

Cheers

Tony

How about:

• Concrete
• Wood
• Steel bar

etc.?