Forming a Bell (or Hub) in PVC Pipe




This is my first Instructable. I figured I'd start small with a helpful hint. This Instructable shows how to bell the end of a PVC pipe so that another piece can be nested in it.

I was a Peace Corps volunteer for three years. In Panama, I had a chance to work with a few aqueduct projects. These projects basically amounted to laying a PVC pipe in a stream at a high elevation and diverting water over a distance to a home or field kitchen. PVC pipe in Panama comes with a bell (or hub) on each end of the tube, so consecutive pieces can be nested, one in another, for infinity. This works great for a single line, but eventually you'll have two non-belled ends which you need to join. This could be solved with a coupler and some cement. But, since most of the pipe we worked with in Panama was donated, and the patrons never thought that far ahead, people learned to improvise. Using fire, you can soften the PVC to the point that you can work another piece inside it, such that a bell is formed. I had to use this technique recently, while installing some electrical conduit. I found myself closer to a blow torch than to a hardware store, so I figured the belling technique was the way to go.

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Step 1: Materials

PVC Pipe: I used 1" electrical conduit. This could work for other sizes, but I imagine thinner-walled pipe would be easier to work with on this technique.
Pipe Cutter: or a hacksaw.
Fire: I used a blow torch. In Panama, the people were prone to use camp or cooking fires. Either works. After I took photos of this demo, I was informed that a heat gun works for this technique, as well, without the scorching.
"Round file": this is optional and is used the remove any scorched material.

Step 2: Cut Pipe to Length

If you're being precise, you should add maybe 1/4" to the length of the pipe you're using. Also, you'll need a small piece of pipe at least 2" long, in the same diameter as the pipe you're working with. This will be your mold.

Step 3: Soften the Pipe

Warning: It was pointed out in the comments (and I experienced this while taking these photos) that heated and burning PVC gives off some nasty fumes. Do this in a well-ventilated area, and keep your work at a distance to avoid inhaling any toxic gases.

Light the torch, keeping the flame low. Take the piece of pipe you want to bell and hold the end at the tip of the flame. Keep it rotating, trying to avoid charing it, and soften the last 1" of the piece. Now soften the inside wall of the same section of pipe (you'll feel hot air coming out the far side of the pipe if you're doing this right). Remember to keep your distance and avoid flame-ups. After a few seconds, move back to heating the outside of the pipe. Eventually it will start to droop a little. It should be good to go.

Step 4: Shape the Bell

Insert the extra bit of pipe into your bell-to-be. Work it in until it's about 1" into the softened pipe. The bell will be evident now. Keep the mold in there for about 5 minutes while the pipe cools and hardens. When you remove the mold, the bell should retain it's shape. If the pipe charred on the inside, gently remove any residues with a round file.

Step 5: Use As Needed

This technique is probably OK for electrical conduit, but I would hesitate to use it on potable water lines. I recommend against ingesting the chemical byproducts of burnt (or even just heated) PVC. Also the heating probably weakens the plastic, so this would be a no-no on pressurized lines.

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    8 Discussions


    10 years ago on Introduction

    Except for the yukky charring, there should be no water potability orstrength problems from heating and cooling pvc.  Its how the pvcpipe was made in the first place.  I don't know if PVC is ok fordrinking water though.  But heating and cooling thermoplastic thatis rated for potable water will not affect its rating.


    10 years ago on Introduction

    When heating the pipe try and take a little more time and keep your flame further away. If you do this the pipe will be less likely to char. I work as a construction electrician and have used this technique, but have also heated PVC just to bend it. Very rarely do we burn the pipe. The only time I see this is when someone heats it too long, too close or heats and then bends and heats again to add or subtract the bend.

    2 replies

    Reply 10 years ago on Introduction

    Thanks for the feedback. I'll try it with the heat gun next time I get a chance. That should prevent the scorching all together.


    Reply 10 years ago on Introduction

    After testing, the heat gun is much more effective with no scorching. It will be my tool of choice, next time.


    10 years ago on Introduction

    Boiling water works for this process as well but it is slow. Heated cooking oil in a pot works too--you can dial in the right temperature with a thermometer and trial & error.


    10 years ago on Introduction

    Great and useful Instructable, but please include a warning. Fumes dangerous to your health are released when heating/burning PVC like this. The project should only be pursued where there is adequate ventilation. Other than that, though, good info. I've got some PVC here I'm about to use in an antenna experiment, and the simple technique you posted will be a lot better than using a bunch of fittings or tape.

    2 replies

    And one more thing which I'm sure applies to many in the Instructables community: Thanks for volunteering. In a world that sometimes seems hopeless, your efforts have made hope a reality for someone.