# PVC Piping - help me, because I have no clue. **URL:** \ **Category:** Factual Questions\ **Created:** [June 10, 2008, 3:10pm UTC](https://boards.straightdope.com/t/pvc-piping-help-me-because-i-have-no-clue/452447 "2008-06-10T15:10:37Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![ReuvenB](https://avatars.discourse-cdn.com/v4/letter/r/9fc348/32.png) [@ReuvenB](https://boards.straightdope.com/u/ReuvenB)\ **Post date:** [June 10, 2008, 3:10pm UTC](https://boards.straightdope.com/t/pvc-piping-help-me-because-i-have-no-clue/452447/1 "2008-06-10T15:10:37Z")
I’m performing an experiment where I have to build a ~1 meter length of PVC pipe that a large steel ball bearing can fall through. There are three catches, though: 1. The interior of the pipe has to have a low-grade vacuum. 2. I need to be able to vary the length of the pipe(don’t need to have much fine control over the height, being able to change it in 10cm increments is okay). 3. I need to be able to gain access to the interior of the pipe easily. Now, one is mostly covered; I have a vacuum pump and hosing for it. Number two is what’s stumping me. I figured that I would do is buy a bunch of small attachments that I can screw together, then seal with window sealant. Unfortunately, I know next to nothing about piping and fitting, and the jargon is ridiculous. What is the name for this kind of thing, and is there a better way to do it? ---
**Author:** ![Finagle](https://avatars.discourse-cdn.com/v4/letter/f/b19c9b/32.png) [@Finagle](https://boards.straightdope.com/u/Finagle)\ **Post date:** [June 10, 2008, 3:23pm UTC](https://boards.straightdope.com/t/pvc-piping-help-me-because-i-have-no-clue/452447/2 "2008-06-10T15:23:26Z")
I don’t know if it would work, but I suppose you could use two different diameters of PVC pipe to make something like a trombone slide. Then take a large inner tube and make a sleeve around the sliding joint, sealing it with rubber cement (e.g. Plumbers Goop). Use an endcap on the top of the PVC pipe to allow access. Or…you could just buy X different lengths of PVC pipe if you’re doing a science experiment. Line them up side by side and do them one at a time. ---
**Author:** ![Lanzy](https://avatars.discourse-cdn.com/v4/letter/l/74df32/32.png) [@Lanzy](https://boards.straightdope.com/u/Lanzy)\ **Post date:** [June 10, 2008, 3:31pm UTC](https://boards.straightdope.com/t/pvc-piping-help-me-because-i-have-no-clue/452447/3 "2008-06-10T15:31:10Z")
Are you doing this for a class? ---
**Author:** ![Santo\_Rugger](https://avatars.discourse-cdn.com/v4/letter/s/e95f7d/32.png) [@Santo\_Rugger](https://boards.straightdope.com/u/Santo_Rugger)\ **Post date:** [June 10, 2008, 3:39pm UTC](https://boards.straightdope.com/t/pvc-piping-help-me-because-i-have-no-clue/452447/4 "2008-06-10T15:39:07Z")
Going of **Finagle** ’s idea, you can set up whatever you need to set up on the end, and have a male (or female) joint on that end. Then, cut 10 sections of pipe, of 10cm, 20cm, etc. lengths, up to 1m. If you buy two 10ft sections of pipe, you should be able to do this with two pipes (the first would have a 100cm, 90cm, 80cm, and 20cm section cut out of it. The second would have a 70cm, 60cm, 50cm, 40cm, 30cm, and 10cm.) Put a female (or male) joint at the end of that section. You can do the same for the opposite end if you need connections at both sides. You may be able to get away with using an O-ring instead of window sealer, which would greatly improve the modularity. ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [June 10, 2008, 4:40pm UTC](https://boards.straightdope.com/t/pvc-piping-help-me-because-i-have-no-clue/452447/5 "2008-06-10T16:40:01Z")
[QUOTE=Santo Rugger] You may be able to get away with using an O-ring instead of window sealer [/QUOTE] Or (if, as seems likely, a perfect & durable seal isn’t required) you might simply tape the joints. ---
**Author:** ![masterofnone](https://avatars.discourse-cdn.com/v4/letter/m/4bbf92/32.png) [@masterofnone](https://boards.straightdope.com/u/masterofnone)\ **Post date:** [June 10, 2008, 4:51pm UTC](https://boards.straightdope.com/t/pvc-piping-help-me-because-i-have-no-clue/452447/6 "2008-06-10T16:51:00Z")
[QUOTE=Finagle] I don’t know if it would work, but I suppose you could use two different diameters of PVC pipe to make something like a trombone slide. Then take a large inner tube and make a sleeve around the sliding joint, sealing it with rubber cement (e.g. Plumbers Goop). [/QUOTE] You could also use petroleum jelly if the pipes fit tightly enough. ---
**Author:** ![gotpasswords](https://avatars.discourse-cdn.com/v4/letter/g/c57346/32.png) [@gotpasswords](https://boards.straightdope.com/u/gotpasswords)\ **Post date:** [June 10, 2008, 5:01pm UTC](https://boards.straightdope.com/t/pvc-piping-help-me-because-i-have-no-clue/452447/7 "2008-06-10T17:01:25Z")
Going off \*\*Finagle’s \*\* idea to just cut a bunch of lengths - PVC pipe is dirt cheap - at the bottom end where the vacuum is to be attached, you could use a “compression repair coupler” to go between the various-sized pipes and the vacuum pump. Here’s one [in pieces](http://www.troubleshooters.com/pool/repipe/images/piping_compression_coupling_disassembled.jpg) and [one assembled.](http://www.sisale-international.com/pic/20071112134156.gif) These things withstand regular water pressure permanently, so they should be able to handle a light vacuum. A light smear of vaseline on the rubber seals will help with the seals and help you slide the pipes in and out. ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [June 10, 2008, 5:12pm UTC](https://boards.straightdope.com/t/pvc-piping-help-me-because-i-have-no-clue/452447/8 "2008-06-10T17:12:36Z")
There are some pictures of the construction of a PVC syringe type water gun [in this thread](http://forums.sscentral.org/t3955/) that you may find useful. O-rings and grease will hold water under pressure, so they’ll also hold some vacuum. ---
**Author:** ![ReuvenB](https://avatars.discourse-cdn.com/v4/letter/r/9fc348/32.png) [@ReuvenB](https://boards.straightdope.com/u/ReuvenB)\ **Post date:** [June 10, 2008, 10:48pm UTC](https://boards.straightdope.com/t/pvc-piping-help-me-because-i-have-no-clue/452447/9 "2008-06-10T22:48:12Z")
[QUOTE=Lanzy] Are you doing this for a class? [/QUOTE] Nope, research under a professor. His suggestion was to get a bunch of male-female connector/adaptor/i don’t know the word and just screw them on one by one to vary the height. ---
**Author:** ![Nanoda](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Nanoda](https://boards.straightdope.com/u/Nanoda)\ **Post date:** [June 11, 2008, 4:00am UTC](https://boards.straightdope.com/t/pvc-piping-help-me-because-i-have-no-clue/452447/10 "2008-06-11T04:00:45Z")
This may not be solving the right problem, but could you just draw the steel ball up the tube from the outside with a magnet to different levels, then remove the magnet to release? Then you just need one long tube, with perhaps a more permanent seal. If you need more accuracy on release time, you could use an electromagnet. ---
**Author:** ![ReuvenB](https://avatars.discourse-cdn.com/v4/letter/r/9fc348/32.png) [@ReuvenB](https://boards.straightdope.com/u/ReuvenB)\ **Post date:** [June 11, 2008, 4:03am UTC](https://boards.straightdope.com/t/pvc-piping-help-me-because-i-have-no-clue/452447/11 "2008-06-11T04:03:12Z")
[QUOTE=Nanoda] This may not be solving the right problem, but could you just draw the steel ball up the tube from the outside with a magnet to different levels, then remove the magnet to release? Then you just need one long tube, with perhaps a more permanent seal. If you need more accuracy on release time, you could use an electromagnet. [/QUOTE] Unfortunately, no. The ball needs to be dropped in a certain orientation, with as little spin while falling as possible. ---
**Author:** ![Projammer](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/projammer/32/559_2.png) [@Projammer](https://boards.straightdope.com/u/Projammer)\ **Post date:** [June 11, 2008, 3:57pm UTC](https://boards.straightdope.com/t/pvc-piping-help-me-because-i-have-no-clue/452447/12 "2008-06-11T15:57:01Z")
Couple of suggestions. Make some sort of release mechanism that you can slide down into the pipe to drop the ball at whatever level you desire. Or. To minimize the number of joints, make your pieces 10, 20, 30, and 40 cm long. You’ll be able to combine them for any length up to 1 meter. Then lightly sand the outsides of the ends so they just snugly fit into a coupling. You shouldn’t need any sealant at all. Or just a light oil.