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Pump fitted to mains

Discussion in 'Plumbing Forum' started by UKMax, Apr 9, 2011.

Discuss Pump fitted to mains in the Plumbing Forum area at

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  1. UKMax

    UKMax Guest

    Hi all,

    Really great to be treated to your hands-on experience. Thanks.

    I'm not a plumber, but I am a mechanical engineer working on fluid systems, which is similar, and I've come across something that confuses me.

    My plumber explained that he cannot connect pump to the mains water supply to supply a shower (the hot water comes from a tank so is OK). I accept this may be the case, but why?

    Is it because of the mains pressure being a bit high for pump inlet (they are typically max 1 bar)? Is it a 'catch-all' reg to stop someone abusing the mains supply (in which case it doesn't really apply to one shower). Is it something else?

    I stress I'm not looking for a reason to cheat the reg, but I genuinely don't understand the technical reason for the ban. Can you help?

  2. Howsie

    Howsie Plumber

    You can draw upto 12l/m from the mains via a pump so I guess you'd be OK for the shower. Anymore than this and the WU would have a problem getting the minimum pressure to the rest of the community.
  3. fuzzy

    fuzzy Guest

    you couldnt be allowed to pump mains as you could draw more water from the main than you should and starve other properties of water. you could even, if the pump was strong enough create a situation you draw water from somebody elses water from their property
  4. UKMax

    UKMax Guest

    Thanks, guys.
    So given the original idea was to pump a shower, there is no pure technical reason why you can't pump the mains, just a catch-all reg? After all, one shower couldn't starve a neighbouring property. If you think of the relative pipe sizes etc, a normal shower pump motor (<0.3KW) would burn out long before you sucked water that volume of water thru' a 15mm pipe!!

    I thought it may be the case that it was just a catch-all reg, as I cannot think of a technical reason, but it's good to see you guys agree.
  5. PlumbingSucks

    PlumbingSucks Guest

    its to prevent contamination of the water supply in the unlikely event that say the water board had turned off the streets water supply and next door are filling the pond with a hose with no check valve on and you turn on your shower and pull dirty water from the pond into the water main.
  6. fagsanbooz

    fagsanbooz Guest

    spot on! water companies say that only a small drop in mains pressure for a short period of time can create backflow conditions. They estimate this happens every few minutes around the country and can be due to a number of things. remember also you can only 'pull' whats available and your mains pipework will have a limit on what you can pull in.
  7. darrenangel

    darrenangel New Member

    I think also, if you pump mains water it can cause dirt and mud to get sucked into the mains pipe if there is a crack in the pipe. obviously contaminating the main supply.
  8. fuzzy

    fuzzy Guest

    i wouldnt call it a catch all reg, lots of things can affect pressure, if you have any type of pump pulling it could cause back flow and therefore contamination. you cannot fir a pump to the mains. you need a cistern and therefore an air gap
  9. Howsie

    Howsie Plumber

    I understood that you could pump the mains upto 12l/m and then after that you had to seek approval from the WU.
  10. WHPES

    WHPES Trusted Plumber GSR

    If you are wanting a mixer shower fitting then it is incorrect to have unbalanced hot and cold. The correct way is to bring the cold feed from the DHW cistern in the loft. If supply is a problem you need to change your cistern for a larger one.
  11. ocentric

    ocentric Guest

    I don't think so - I thought the only way to pump the mains and comform with the water regs is to have a breaker tank & pump that
  12. ecowarm

    ecowarm Guest

  13. electron

    electron Member

    Are Fire Hydrants on the same system as domestic consumer? Surely a Fire Pump pulls more than 12 Litres/min.
  14. PlumbBobBob

    PlumbBobBob Guest

    i presume they have special dispensation to do this as waiting for permission can be a case of life and death.
  15. UKMax

    UKMax Guest

    Thanks, all.
    I've been thinking about this, and some things make sense, and others don't. I can well understand the possibility of the mains pressure dropping and contamination being sucked in if someone nearby had pumped the mains.

    Some of the other reasons given make less sense though. The balance question doesn't really make sense if both hot and cold are pumped by the same pump, does it?

    There were lots of other reasons given, but if these are true, what about pressure washers? These pump the mains, and nowadays everybody has one? How can it be bad for a shower pump but OK for a Karcher 25L/min beast?

    Anyway, truly grateful for all the advice. Thanks
  16. fuzzy

    fuzzy Guest

    outside taps have alot of regs on em, double check valves etc

    you want to pump the hot and cold, is the hot pressurised? how is the hot fed?
  17. UKMax

    UKMax Guest

    Hi Fuzzy

    Not pressurized.

    Hot is direct from tank, as will the cold be now (from loft tank), but what I didn't understand was why the cold could not come from the mains.

    The pressure would have to be stepped down to around 0.5 bar (similar to hot), I accept, but flow would then be similar if pumped by a twin impeller pump. I just couldn't see where the balance question came in, unless the other poster meant the pressure.

    Interesting point about regs for outside taps. I had a plumber fit one last year, and he simply tee'd into the kitchen mains and thru' the wall. No check valves etc. I also see the kits you can but at diy places, and they just seem to be a tap and connector. My point is I bet lots of people have this sort of arrangement, and man y will use pressure washers. Surely the principle is the same? You can either pump the mains or you can't, and if you can't millions of people are breaking the rules with pressure washers?
  18. Howsie

    Howsie Plumber

    A pressure washer is not a permanent connection to the water supply and should be connected to an outside tap with the appropriate check valves in place.
  19. darrenangel

    darrenangel New Member

    You can buy outside taps with check valves in built.
  20. WHPES

    WHPES Trusted Plumber GSR

    Those are only allowed for replacing the tap where an existing installation exists and must not be used for new installations
  21. WaterTight

    WaterTight Plumber

    i wonder why though - surely a check valve is a check valve.
  22. fagsanbooz

    fagsanbooz Guest

    preferably new outside taps should have double check 'inside' on pipework from mains to protect from frost etc but when replacing an existing tap, if no check valve fitted then a tap with valve inside it, is suitable
  23. plumberdarren

    plumberdarren Guest

    howsie is right 12 l/m say the water regs, i would get a bigger tank if needs be and run a seperate cold feed from it to a pump to enable equal pressure.
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