(206) 949-5683, Top Rated Plumber, Seattle
Page 1 of 2 12 LastLast
Results 1 to 15 of 25

Thread: Why can't I Dry-fit PVC fittings?

  1. #1

    Default Why can't I Dry-fit PVC fittings?

    What is the trick to being able to dry-fit PVC fittings before final assembly? I am working with 3" PVC fittings from Lowes, plumbing up the waste line to the new toilet location in our bathroom remodel. I'd like to put the three fittings together and mark them before I get out the cement so that I can be sure the slope of the line is correct and that the closet bend is going to be in the exact right position, height, and level once the cement sets. But, the fittings just don't slide together -- If I really work at it, I can get them seated about halfway, but that's not good enough.

    Once I put primer and cement on them, they slide right together and seat all the way, so I don't think there's anything wrong with the fittings.

    I only get one shot at this, and if I mess it up I'm going to be cutting into the ceiling and wall in the room below the bath to get at the tee that I ruin on the stack.

  2. #2
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Location
    Cave Creek, Arizona
    Posts
    25,687

    Default pvc

    That is the way it is supposed to work. PVC joints are called "interferrence fit" which means they are tight when dry so there is no excess space that has to be filled with cement when they are assembled. If you remove any roughness on the end of the pipe, you may get them together a little further, but if they fit all the way, when dry, the joints would not be good enough once it is assembled.

  3. #3
    Plumber jimbo's Avatar
    Join Date
    Aug 2004
    Location
    San Diego
    Posts
    9,001

    Default

    Well, this is why Do-it-Yourself sometimes becomes Do-it-Over. Some things are learned only be experience. Your only cost will be to replace some fittings if you don't get it just right the first time. If time is valuable to you or at a premium, then this is where you hire someone who will get it right the first time.

    This is not meant to be a criticism of DIY, because at home I tackle any job in any trade. Some jobs go better than others, and I just accept that fact.

  4. #4
    DIY Senior Member captwally's Avatar
    Join Date
    Apr 2005
    Location
    Florida
    Posts
    102

    Default

    The reason PVC cement is called "solvent weld" is exactly the reason the facts have been stated by knowledgeable people before I got to the thread. PVC fittings are not 'glued' together, they are welded with the cement. The glue is not actually a separate entity connecting two parts, rather it is a solvent that chemically liquifies the PVC itself creating a bond that in effect is melting the parts together.

    The parts do not fit together dry because the tolerances are so thin to make an effective joint. When the 'glue' is applied, the parts slide together all the way because the plastic has actually been melted at the point of connection. Once that connection cures, it is essentially one solid piece of PVC, not two pieces glued together.

    If you want to ensure a proper fit you must measure and cut where the fittings will be in the final assembly, not in a dry fit situation.
    Measure Twice, Cut Once
    Wally

  5. #5
    Mechanical Engineer SteV8e's Avatar
    Join Date
    Nov 2006
    Location
    Minneapolis, MN
    Posts
    5

    Default

    I ran into that dry-fit problem too. My application is different because I am using the pvc to build frames. My son and I are building a trebuchet and the frames will be 2" pvc. The treb will be made of two complex 3D frames that are a mirror image of one another. Each half includes a double wye, 4 90elbows, 4 45elbows, 2 Tees, and 2 adapters with square-head plugs (the frame will be filled with water for lauch stablility).

    Because of the complexity and not dry fitting, it is hard to build. If I had 3D CAD models of the fittings, I would know the exact lengths of the pvc pipe needed. Does anyone know if there are CAD models available?

    I am doing this project with my son to teach him some engineering and applied math. He is interested in hurling objects long distances.

    Thanks
    Silence is Golden
    Duct Tape is Silver

  6. #6

    Default

    PVC pipe is also slightly flexible so usually putting the pipe next to the fitting and marking will give a good enough measurement.
    (important note: I'm not a pro)

  7. #7
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    Location
    New England
    Posts
    21,448

    Default

    Many of the fittings have a definite lip inside them. You should be able to insert the pipe in the fitting until it bottoms against that ridge or lip once it is primed and slobbered with the solvent.

    Don't overload the pvc, it can shatter into some nasty shards if you exceed its strength. It will bend a bunch first, though ,and is sensitive to temperature. Also note, it changes length a fair amount with temperature.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  8. #8
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Location
    Cave Creek, Arizona
    Posts
    25,687

    Default measure

    That is why they make rulers so you can calculate the fitting's dimensions as far as insertion depth.

  9. #9
    DIY Senior Member Phil H2's Avatar
    Join Date
    Sep 2006
    Location
    Tujunga, CA
    Posts
    125

    Default

    I don't know if PVC fittings have standard dimensions (galv/blk iron have standard running length dimensions, copper fittings do not and they vary from one manufacture to the next). If you know the fitting manufacture, you could check their website to see if they have CAD models. Spears Manufacturing has dimensions for their PVC fittings on the web (http://www.spearsmfg.com/).

  10. #10
    Mechanical Engineer SteV8e's Avatar
    Join Date
    Nov 2006
    Location
    Minneapolis, MN
    Posts
    5

    Default

    Phil:

    Thanks for the link to Spears; it has detailed dimensions for the fittings. I had received some specs from McMaster-Carr for the manufacturere Nibco, but not as detailed as the Spears drawings.

    I had to delete the ) from the end of the Spears link to get it work.

    I think that I will need to make the ProE CAD files myself. Let me know if you would like me to send them to you.
    Silence is Golden
    Duct Tape is Silver

  11. #11
    DIY Senior Member ToolsRMe's Avatar
    Join Date
    Mar 2006
    Location
    CO
    Posts
    145

    Default

    Can you use ABS instead of PVC?

  12. #12
    In the Trades Gary Swart's Avatar
    Join Date
    Sep 2004
    Location
    Yakima WA
    Posts
    7,246

    Default

    You can't dry fit ABS either.

  13. #13
    DIY Senior Member ToolsRMe's Avatar
    Join Date
    Mar 2006
    Location
    CO
    Posts
    145

    Default

    Quote Originally Posted by Gary Swart
    You can't dry fit ABS either.
    I've installed a central vacuum system in my house and routinely dry fit the ABS stuff.

    Now that may be different than the ABS you use for water plumbing since I needed to get that stuff at a vacuum cleaner store.

    Live and learn.

  14. #14
    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
    Join Date
    Nov 2005
    Location
    Central Florida
    Posts
    2,687

    Default

    My central vac used PVC, not ABS, but it was dry-fittable as well. In fact, I installed a large part of the system by dry-fitting and taping the outside of the joints with electrical tape. (It was temporary, waiting for some other construction to be completed.) It's a special thin-wall pipe designed to maximize the inside area for the outside diameter. Fits are sloppy, but once welded they're pretty strong.
    Last edited by Mikey; 11-21-2006 at 04:43 PM.

  15. #15
    In the Trades Gary Swart's Avatar
    Join Date
    Sep 2004
    Location
    Yakima WA
    Posts
    7,246

    Default

    The PVC used for vacuum systems is not the same as that used for drains. Go back up this thread and read HJ's reply regarding how PVC pipe/fittings are made and fit. Fitting PVC is really no different than fitting copper. I use a marking pen when working with PVC and copper to mark where I will cut the pipe. It's really not rocket science.

Similar Threads

  1. bronze fittings and copper fittings
    By diyfun in forum Plumbing Forum, Professional & DIY Advice, Tips & Tricks
    Replies: 6
    Last Post: 02-12-2012, 12:03 PM
  2. PEX Fittings
    By Daniel73 in forum Plumbing Forum, Professional & DIY Advice, Tips & Tricks
    Replies: 7
    Last Post: 06-30-2009, 06:12 AM
  3. re-using fittings
    By samlin7 in forum Plumbing Forum, Professional & DIY Advice, Tips & Tricks
    Replies: 19
    Last Post: 12-29-2007, 04:03 PM
  4. Pex Fittings
    By wingam00 in forum Plumbing Forum, Professional & DIY Advice, Tips & Tricks
    Replies: 3
    Last Post: 03-13-2006, 12:17 PM
  5. schedule 40 dwv fittings and pressure fittings
    By Ed from chicago in forum Plumbing Forum, Professional & DIY Advice, Tips & Tricks
    Replies: 8
    Last Post: 09-02-2005, 07:14 PM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •