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Discuss How Can I increase shower drain flow rate in the Plumbing Forum area at

  1. Tommy Abdy Collins

    Tommy Abdy Collins New Member

    I have fitted a shower tray using the drain provided which has a 40mm drain. The drain is not coping with the output of water from the shower head. If I fit a larger diameter pipe to the 40mm outlet, will this increase the volume of water being drained? - even though it will start by exiting through the 40mm pipe.

    I think my solution is either to reduce the output of water from the shower head with a restrictor or fit a different drain with a larger diameter outlet.
  2. king of pipes

    king of pipes Trusted Plumber GSR Top Contributor!!

    Correct ! sometimes you may be able to remove a cup like device in the trap which is meant to trap hair and debris to gain extra draining , but its better for your wallet and the environment to install restrictors in the shower outlets limited to 8 litres a minute that would be my advice . Kop
    • Like Like x 4
  3. sammathias

    sammathias Plumber GSR

    Or a high flow shower trap :)
    • Agree Agree x 2
    • Like Like x 1
  4. YorkshireDave

    YorkshireDave Plumber Top Contributor!!

    By removing the cup, you remove the water blocking foul smells coming back up. Sorry, not a good idea.

    FWIW, id strongly suspect pipework its connected to. If it flows fine at first its def pipework. My experience is poorly supported pipe that simply fills up with solids over the years.
    • Like Like x 3
  5. scott_d

    scott_d Plumber GSR Top Contributor!!

    High flow shower trap if it's not too late.
    How many litres per are we talking?
    • Like Like x 2
  6. Harvest Fields

    Harvest Fields S. Mod Trusted Plumber GSR Top Contributor!!

    I would do as above and try to fit a fast flow trap
    • Agree Agree x 2
  7. Tommy Abdy Collins

    Tommy Abdy Collins New Member

    Many thanks to those who have replied. Someone off the forum suggested that running the trap, which has a 40mm exit pipe, into a larger diameter pipe would increase flow. I'm not sure that is correct. Surely the 40mm pipe will continue to restrict and all I would achieve is a lower pressure beyond - it would not increase volume leaving the shower tray. Would you agree with me or have I got my physics wrong.
    • Agree Agree x 1
  8. fixitflav

    fixitflav Active Member

    IMO it depends where you change to 50mm. If you currently have a fair length of 40mm after the trap, changing that to 50 might help.
    But are you sure the current system is clear of debris?
  9. Tommy Abdy Collins

    Tommy Abdy Collins New Member

    I could change to 50mm within inches after the trap. The run to the drain is only about 3ft then vertically down and it is clear of debris. I think the shower which is electric boost pumped water is supplying too much and I need to fit the restrictor which came with the shower head. The customer reckons his old system which had 3 nozzles in the walls as well as the head produced a much larger volume of water but I have my doubts as presumably all these systems are designed around some reasonably common output quantities to match the 'average' supply. I'm not a plumber by trade - hence my rather basic questions. I'm using my fairly extensive DIY skills to help a friend and not had this problem with various showers I've fitted in my own homes.
  10. scott_d

    scott_d Plumber GSR Top Contributor!!

    If you can reach the trap fit a mcalpine hi flow unit
    They can take something like 30 litres per minute, says in the instructions
  11. Best

    Best Trusted Plumber Top Contributor!!

    If you presently have a standard low flow trap then it will restrict the flow - the waste grid is the biggest restriction.
    That is why high flow traps are basically a full open trap at top and the mushroom cap on top is only for cosmetic purpose.
    You do need shower trays that suit a 90mm trap.
    Putting in a larger waste pipe is pointless if you still have a restriction at trap
    • Winner Winner x 2
    • Like Like x 1
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