(206) 949-5683, Top Rated Plumber, Seattle
Results 1 to 5 of 5

Thread: P Trap Physics

  1. #1
    DIY Junior Member rafigso's Avatar
    Join Date
    Sep 2012
    Location
    Greensboro, NC
    Posts
    8

    Default P Trap Physics

    Good afternoon
    When you turn on the water, and the P-trap begins to fill, what "forces" push the water through the "U" and out through the arm.

    Just curious.

    Thanks,
    Rafael

  2. #2
    Forum Admin, Expert Plumber Terry's Avatar
    Join Date
    Aug 2004
    Location
    Bothell, Washington
    Posts
    14,195
    Blog Entries
    1

    Default

    When you turn on the water, and the P-trap begins to fill
    The p-trap is full before you start. The trap can only hold so much water, so any added water passes right through. Without the constant water seal, you would have sewer smell floating up in your face. Cool huh?

  3. #3
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    Location
    New England
    Posts
    21,390

    Default

    Basically, gravity is doing it's thing. The water pushing down from the sink or whatever fixture takes the path of least resistance by being pushed through the trap and out, but because of the U-shape, some stays 'trapped' there to seal the fixture from the sewer gasses. That's one reason why it is so critical to keep the angles and distances correct for it all to work right.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  4. #4
    DIY Senior Member Hammerlane's Avatar
    Join Date
    Oct 2011
    Location
    Ohio
    Posts
    252

    Default

    Like Terry mentioned hopefully the p-trap is full before new draining water in introduced.
    The trap can only hold so much water. So as new water is introduced to the trap, this new(falling) water has kinetic energy. Being that all water is seeking its lowest potential(thanks to gravity) and with the proper slope of the trap arm, the displaced water will flow from the energy it obtained from the falling (draining) water.

    Hmmmmm??
    Last edited by Hammerlane; 11-16-2012 at 06:50 PM.

  5. #5
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Location
    Cave Creek, Arizona
    Posts
    25,624

    Default

    Waater is a liquid, so it "seeks its own level". Any water added to one side side of the trap will cause the other side to try to reach the same level, but since there is no barrier to contain it, the water flows down the drain. In the meantime the added water also dropping to maintain an even level with the outlet. When the water stops flowing, the two sides will be in equalibrium and the trap will still be full of water. If the "P" trap is not vented properly, then it becomes an "S" trap with a completely different set of dynamics.
    Licensed residential and commercial plumber

Similar Threads

  1. Shower diverter pops up by itself. Also, a bonus physics/pressure question.
    By janicki in forum Plumbing Forum, Professional & DIY Advice, Tips & Tricks
    Replies: 9
    Last Post: 07-12-2012, 06:51 PM
  2. P-Trap into floor drain? Or is that an S-Trap? (and not good)
    By bretm1 in forum Plumbing Forum, Professional & DIY Advice, Tips & Tricks
    Replies: 4
    Last Post: 04-22-2011, 07:19 AM
  3. Well Physics
    By weather777 in forum Pumps and Tanks Well Forum & Blog
    Replies: 18
    Last Post: 01-23-2009, 01:50 PM
  4. Replace S-trap with P-trap or chicago loop?
    By staceyneil in forum Plumbing Forum, Professional & DIY Advice, Tips & Tricks
    Replies: 4
    Last Post: 03-05-2007, 08:06 AM
  5. Vanity sink trap - can I use 90's after the trap?
    By chassis in forum Plumbing Forum, Professional & DIY Advice, Tips & Tricks
    Replies: 10
    Last Post: 01-16-2006, 06:40 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
  •