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New shower trap not draining well.

Discussion in 'Plumbing and Central Heating' started by hexdex, 30 Aug 2017.

  1. hexdex

    hexdex

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    I know this seems to be a well trodden problem, but I can't make sense of why it's happening, or what solution there is for my situation.

    I've just finished a complete refit in our bathroom and installed a standard P trap for the bath, an anti siphon bottle trap on the sink and the Mcalpine (ST90CP10-70) shower trap which is very slow to drain with the mushroom cap on, but take it off and the water drains fast. The 40mm waste drops more than enough from the trap and into a 40-60mm reducer/enlarger connected to 60mm waste which, together with waste from the bath and sink, drains down into the main sewer pipe....being a downstairs bathroom with timber floor, this is direct with no access to the pipe outside. Immediately outside, there is a vent pipe, but this is after the drainage goes into the sewer pipe.

    I hear mention that with all connections from bath, sink and shower sharing the same waste (as mine does), it can cause vacuum issues and that one solution would be some kind of vent on the shower waste, but as there is no room for this it's not an option.

    Is there anything I can do to fix this? It's now been fully tiled, but if need be, I can just about gain access via the next room and scrambling about under the timber flooring, so are there better options for faster shower draining other than this kind of trap?

    Thanks.
     
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  3. Jackrae

    Jackrae

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    On the basis that the trap drains well with the cap off then it's probably the lather in the water restricting the flow into the trap. Maybe that sounds daft but air bubbles in the lather reduce the effective draining area through which the water has to flow. This type of problem is particularly troublesome if you have installed one of those ridiculously shallow shower trays which permit no depth of water before they start to overflow.
     
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  4. hexdex

    hexdex

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    I must say that when I take a shower, it's not too bad. But when the girls are in there it's lather city and it was my thinking that this was the cause. I just didn't expect it to be such an issue as people have been known to use a lot of suds before, particularly the female variety.

    The shower tray is a shallow type, but not one of those virtually flat ones. I guess it's around 15mm near the plug. So do I have any alternatives or workarounds? If I chose to install a different trap, are there any that work better than others in this type of situation?

    Thanks.
     
  5. Post a picture of the trap; mushroom on and off, and try disconnecting the basin waste to see if the shower drains quicker. If it does, then you've got a vaccum problem, and you need an AAV type basin waste.
     
  6. Jackrae

    Jackrae

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    shower trap which is very slow to drain with the mushroom cap on, but take it off and the water drains fast
     
  7. I picked up on that Jackrae, I was suggesting he disconnect the BASIN waste (should have added after the seal) to see if there's a vacuum effect issue. Nothing to do with the mushroom cap, just another test to see where the problem might lie.
     
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  8. hexdex

    hexdex

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    Thanks guys, I'll try that tomorrow. I'll also post the pick up too. So can I ask what the difference is between an aav and anti cyphon which I already have on the sink?
     
  9. dilalio

    dilalio

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    How many lpm does your shower head output? And how many can the tray dispose of with the cap on the drain - simple as that really. Just remove the cap!
     
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  11. The mushroom cap is there to create a seal, and stop smells coming back up the drain,so as long as it goes back on after your shower, that wouldn't be an issue.
     
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  12. Jackrae

    Jackrae

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    Are you sure ? Most are merely cosmetic - at least the ones I've seen are. The trap is usually the plastic bowl arrangement which is fitted to the underside of the tray.
     
  13. dilalio

    dilalio

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    They are cosmetic and supposedly for catching hair (which causes further restriction until cleared). Some have holes in the top which aid flow a 'bit'.
     
  14. Madrab

    Madrab

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    Does the mushroom cap have a tube attached that sits down into the shower trap cup? If not then it only there as a cover and doesn't create a water seal, as @dilalio mentions the shower may be feeding more water than the waste can evacuate with the cap on it and you are getting resistance at the cap.
     
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  15. hexdex

    hexdex

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    Just got in an hour ago...busy day! I really will post up some pics tomorrow, but I don't think the cap is purely cosmetic. It sits inside the removable bowl with the water in which creates the 'trap', it also has a rubber seal around it.
     
  16. If there's a tube below the cap, then that's what creating the air trap, and they aren't exactly speed merchants at shifting water.
     
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  17. hexdex

    hexdex

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    Yep, there is a tube on the cap which sits inside the water in the trap. The gap around the cap that water can flow is only around 10mm or so. So add soap to the water and I can see how drainage isn't going to be speedy as you say Doggit. Annoying and silly design in hindsight. Especially annoying because I got this Mcalpine trap following rave reviews on screwfix.

    I have figured out a bodge work around. If I partially unscrew the mushroom and add a washer in the gap, add another fabricated washer of some kind to the cap it screws into, it will raise it. I may have to try that.

    Any other ideas? If I decide to change the trap, what kind would you recommend?

    Thanks.
     

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