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Old 11-15-2012, 12:03 AM   #1
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Best way to join pipe without a fitting?


I am working on a project and need to put many pieces of 2" pipe through a 4" pipe. Rather than spend $1400 on fittings, I've decided to get a 60mm hole saw and just drill holes in the 4" pipe.

Question is, what is the best way to make the seal leak-tight? I'm thinking PVC cement. The only other thing I can think of is silicone, but I don't think it would hold up as well over time.

Is PVC cement the right choice? Is there another option?

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Last edited by tibberous; 11-15-2012 at 09:58 AM. Reason: Explanation on second page.
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Old 11-15-2012, 12:16 AM   #2
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Best way to join pipe without a fitting?


Before I make assumptions, I take it you are planning on using PVC pipe for your project? Exactly how many of these unions are you going to have if you are estimating $1400 in fittings? Leak tight to what extent and under what pressure and flow rate?

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Old 11-15-2012, 12:18 AM   #3
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Best way to join pipe without a fitting?


What is the application?

Doesn't really matter.....if I think I understand what your proposing.....not going to work.

Yes...you can use primer...and then PVC cement to 'glue' those 2" tubes into your 4" header.....as long as you can insure that they will NOT move, and you don't use too much pressure, you 'should' be ok....but....I really doubt you can keep the tubes from moving...

For PVC to have a strong bond...it needs lots of surface area...you are not going to have lots of surface area...

Additionally, there are numerous issues connecting pipes/tubes to a larger round pipe (header).....if you want an idea of what is involved....look at the costruction of radiators.

Good luck...
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Old 11-15-2012, 12:34 AM   #4
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Best way to join pipe without a fitting?


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Originally Posted by ddawg16 View Post
What is the application?

Doesn't really matter.....if I think I understand what your proposing.....not going to work.

Yes...you can use primer...and then PVC cement to 'glue' those 2" tubes into your 4" header.....as long as you can insure that they will NOT move, and you don't use too much pressure, you 'should' be ok....but....I really doubt you can keep the tubes from moving...

For PVC to have a strong bond...it needs lots of surface area...you are not going to have lots of surface area...

Additionally, there are numerous issues connecting pipes/tubes to a larger round pipe (header).....if you want an idea of what is involved....look at the costruction of radiators.

Good luck...
Indeed your contact surface is going to be limited to the thickness of the 4" pipe as far as trying to glue it.

I was thinking you could use something like flexible rubber flashing like for roof vents to both stabilize and seal (so long as the 4" will not be under pressure) but I cannot imagine they will be any cheaper than PVC slip fittings?

Does your 2" material have to be the same as the 4"? What about 2" rubber and 4" pvc. If you could compress the rubber feeding it through the openings it would expand to grip the sides of the hole without any cement? Again, so long as you do not have pressure running through the 4".

And again, just to be sure? Does the 2" connect to the 4" or pass unbroken through it? I read your post as though you were passing it through but ddawg read it as you wanting to connect.

Last edited by user1007; 11-15-2012 at 12:38 AM.
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Old 11-15-2012, 12:36 AM   #5
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Best way to join pipe without a fitting?


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Originally Posted by sdsester View Post
Before I make assumptions, I take it you are planning on using PVC pipe for your project? Exactly how many of these unions are you going to have if you are estimating $1400 in fittings? Leak tight to what extent and under what pressure and flow rate?
I need 96, and there about $15 a pop. They will be under almost no pressure.

I think im going to get the bit i need and do a test run with pvc cement, silicone, maybe even a 2 part epoxy like jb weld. Thought about maybe even using hot glue, no real experiance with it though.
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Old 11-15-2012, 12:41 AM   #6
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Best way to join pipe without a fitting?


PVC cement will be much better than JB Weld in this application. PVC cement will basically melt the PVC....

But, your still back to the 'surface area' issue.
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Old 11-15-2012, 12:51 AM   #7
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Best way to join pipe without a fitting?


http://www.walmart.com/ip/Devcon-506...opper/20370986

i am sure you can find it cheaper
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Old 11-15-2012, 01:29 AM   #8
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Best way to join pipe without a fitting?


I would still search for rubber pipe flashing, rubber sleeves, rubber bushing, etc. that would lock in your drilled hole and grip the pipe passing through. Like in an automotive application where pipes and electrical pass through things, for example.

Last edited by user1007; 11-15-2012 at 01:48 AM.
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Old 11-15-2012, 02:22 AM   #9
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Best way to join pipe without a fitting?


Well, the point is to join, but technically it will pass through - otherwise you'd need to have a curved end on the 2" pipe.

While it would be a ***** to do, fleece + fiberglass would be cheap and pretty-well guaranteed to work. You could wrap the 2" pipe in a 1" strip of fleece, force it 1/2 through the hole, then let the resin soak in the fleece. That's how I made the corners on my waterproof table - took 5 gallons of fiberglass and about 2 weeks to build, but it is incredibly waterproof.
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Old 11-15-2012, 02:31 AM   #10
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Best way to join pipe without a fitting?


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Originally Posted by tibberous View Post
Well, the point is to join, but technically it will pass through - otherwise you'd need to have a curved end on the 2" pipe.

While it would be a ***** to do, fleece + fiberglass would be cheap and pretty-well guaranteed to work. You could wrap the 2" pipe in a 1" strip of fleece, force it 1/2 through the hole, then let the resin soak in the fleece. That's how I made the corners on my waterproof table - took 5 gallons of fiberglass and about 2 weeks to build, but it is incredibly waterproof.
I am confused. It would help to know what you are trying to build?
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Old 11-15-2012, 02:35 AM   #11
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Best way to join pipe without a fitting?


Thermoplastic welding may have some merit in your application .
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Old 11-15-2012, 02:39 AM   #12
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Best way to join pipe without a fitting?


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Originally Posted by Fairview View Post
Thermoplastic welding may have some merit in your application .
Never even heard of that - didn't think it was possible as heat generally deforms and shrinks plastic.
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Old 11-15-2012, 02:52 AM   #13
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Best way to join pipe without a fitting?


Actually welding it might be your best bet if you can get PVC compatible rods. I should think so. I still worry about how much lateral stress your pass through pipe is going exert. Will it slide around?

Anyhow, I looked and even Harbor Freight has plastic welding kits for like $15. You might look for something with an adjustable heat source and pay a bit more though.

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Old 11-15-2012, 08:14 AM   #14
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Best way to join pipe without a fitting?


Sure would like to know what the OP is trying to build. If we knew, someone might be able to suggest an alternative.
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Old 11-15-2012, 08:22 AM   #15
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Best way to join pipe without a fitting?


Without the full info on what it is your really trying to do your just wasting every ones time here having to guess.
You have the benifit of picking the brains of some clever people that have been there done that for free, shame to not use there time wisely.

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