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  1. BobbyJoe

    BobbyJoe Member

    Gravity fed water system
    Two copper pipes in bathroom cupboard which have stops cocks which turn the hot and water supply to the kitchen/bathroom off and on. No stopcock under the kitchen sink.

    Morning everyone, just trying to figure out where do single/double check valves normally go when connecting to the water supply pipework and what is the purpose of them?
    I have a single/double valve fitted on pipes near the toilet and am trying to figure out how many is the norm? Do I just need one or more connected in the flat such as to the bathtub/basin pipes or even the kitchen sink cold/hot water supply.

    Lastly when I use the washing machine and it is doing a load, water comes up into the kitchen sink, is there a reason for this and anything which can be done to prevent it as I took apart the pipes under the sink (white plastic ones) and they were clean no gunk or blockages.

    Thank you for any info/advice
  2. Gareth Harris

    Gareth Harris New Member


    The requirement for single/double check valves depends on the point of use backflow prevention in place.

    For example, in a single domestic dwelling, baths, showers and wash hand basins are considered a fluid category 3 risk:

    An adequate tap gap (usually 20mm) from the spillover level would suffice for taps, and the shower hose should be restrained above the spillover level.

    Where there is no tap gap a double check valve would provide adequate backflow prevention as an alternative.

    Kitchen sinks are considered fluid category 5 - high risk due to the fact you prepare raw meats etc in them, or at least wash things used to prepare raw meats. Again an adequate tap gap would suffice - most modern kitchen taps provide at least a 100mm gap for access.

    There is however another consideration. Are the hot and cold supplies unbalanced? Mains cold and gravity hot? If so, and the water mixes in the body of the taps, you will require single check valves on both supplies to prevent the cold over-pressurising the hot.

    There should also be a stop valve on the mains where it enters the property - this should isolate the whole supply: The Water Supply (Water Fittings) Regulations 1999

    As for the water in the sink when the washing machine is on - I have the same problem so would also welcome any comments on this!!

    Hope this info is useful.
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  3. Last Plumber

    Last Plumber Plumber GSR

    When you say Gravity fed water system, are you meaning Tank fed?

    Single/double check valves?
    Double check valves are more often seen preventing back siphon-age or back-flow into a water main, to prevent contamination. So for example, you would have one on an outside tap and most have them built in.
    Single check valves normally would prevent water flowing in the wrong place or flowing at the wrong time, for example, you may see them on Pumped Heating/ Gravity Hot Water systems, to prevent radiators warming when Hot water only is on. There are many examples of where both these items may be used.

    I suspect you may be using incorrect terminology so I am trying to help by explaining things a bit!

    I suspect you may be looking at Isolation valves. You would see those on Pipes that supply, Taps, WC's, Baths, Ball cocks etc. Does that sound correct?
    They are for convenience and to aid the servicing or repair/replacement of the items they isolate.

    The Washing machine waste problem ( as long as the waste is clear like you say), is most likely due to the run/fall/installation of the pipe after the trap beneath the sink.
    As water is pumped into the trap's connection (from the washing machine waste) the water needs to flow away fast enough to prevent it entering your sink waste. It is difficult to tell you how to solve this without seeing the job but it may help me or others on here if you could perhaps post some photographs.

    Hope this long winded post helps.
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  4. Gareth Harris

    Gareth Harris New Member

    Good points @Last Plumber@Last Plumber on the isolation valves.. I had wondered if that was what was meant.

    As much as they are convenient, servicing valves are required on inlets to all float valves on WC's and cisterns: The Water Supply (Water Fittings) Regulations 1999

    They are certainly a nice to have on taps etc, and I would suggest a good plumber would put them in as standard practice.
  5. moonlight

    moonlight Plumber GSR

    I think you maybe talking about service valves?
    There should be one on every float operated valve. It is good practice to fit them on supplies to basin taps etc. As you have gravity water you would be better fitting full flow ones on supplies to taps.
    • Like Like x 1
  6. BobbyJoe

    BobbyJoe Member

    Thank you all so much for the valuable information, it has been insightful to say the least as I am trying to understand the water system in my flat.

    There is no water tank as there is a gravity fed system via a central plant which supplies water to the entire estate and I believe the cold water feed comes from the mains supply as I can turn off the kitchen and bathroom cold water supply by turning the stopcock in the bathroom cupboard in the off position. There are two stopcocks in the bathroom cupboard one controls the hot water supply to the kitchen&bathroom and the other stopcock controls the cold water supply to the kitchen and bathroom. The water flow/rate was measured at 2 bar as the water pressure in the flat is really good and strong there doesn't seem to be weak pressure since it was switched to the new gravity fed system.

    The previous tenant didn't let anyone in to the flat (I think there was mental health issues according to the neighbours) and he was living here for 20 plus years which explains the "antiqueness" of the place.
    The bathroom is a mess, old suite with looks like the original taps, green stuff on the copper pipes and a funny smell comes from drains. I am not sure if there are servicing valves, single/double valves installed and perhaps the photos attached might you a better idea and apologies you're right I am most likely using the wrong terminology as I am trying to figure this out, thank you in advance for any advice.

    Photos are as follows:
    Bathroom basin pipe from the side (2)
    Toilet pipe next to basin
    Basin in bathroom pipe
    Bathroom cupboard with main rising pipe, two stopcocks one at the bottom which is the cold water supply feed pipe and one at the top which control the hot water feed in the entire flat.










    Last edited: May 15, 2017
  7. BobbyJoe

    BobbyJoe Member

    One last picture inside the bathroom cupboard pipe on the ground and the rest are of the kitchen pipework under the sink.
    There is a small red and blue washing machine isolating valve, which way are they meant to be turned as at present, the red one is turned to the right, if I turn it left water gushes out, the blue one is tilted to the right, if I turn it left it stops the water going into the machine, are they both in the correct positions? I may have to get someone out to check everything as water keeps coming up into the sink when the washing machine is on.




    Last edited: May 15, 2017
  8. BobbyJoe

    BobbyJoe Member

    I don't know if this helps or not but when the boiler (Drayton) was installed along with the radiators, the pipework for them are fixed above the doors see pics they are in the white plastic casing which are placed above door levels.




  9. moonlight

    moonlight Plumber GSR

    You don't have any individual valves on the bathroom basin just earth tags.
    Toilet pipe has a gate valve but the head is missing.
    Picture five, looks like there is just an earth tag.
    The stop taps in the bathroom cupboard would shut all the water off as you said.
    Are the pictures 12 and 13 the kitchen sink?
    It is difficult to make out as the waste pipe is in the way, it looks like there is a check valve on the hot.
    Looking at the first pictures if the earth tag had been fitted further back and soldered elbow used instead of a compression elbow there may have been room to fit a service valve.
    The toilet pipe could be updated so you could have a simple service valve fitted.

    Drayton don't do boilers only controls as far as I am aware. They have hidden the pipework in the trucking as it was probably easier and makes it look reasonable. It was probably the most economic way to install the pipework for the radiators. This is not related to your valves for your water.
    • Like Like x 1
  10. BobbyJoe

    BobbyJoe Member

    Thank you for the reply and yes picture 12 and 13 are of under the sink sorry they aren't very good. The earth wires no longer work because the old hot water cylinder was taken out and a new boiler put in, the earth wires were cut off in the bathroom cupboard but under the kitchen sink/bathroom basin as you can see they are still attached, can I remove them myself?

    If possible can I get service valves installed to the bathroom basin pipework and the bathtub and have a service valve fitted to the toilet pipe?
    How long would it take to get installed and where are they best placed as that would be useful to know.

    I have taken a few more pictures of under the sink and are check valves installed to both the hot and cold sorry about the bad images the last three are a red valve.

    Thank you once again and once I know what needs to be done I will find someone to come out and see what needs updating/fixing.:)





    Last edited: May 16, 2017
  11. Headrush

    Headrush New Member

    The waste below the kitchen sink looks fine to me so long as the trap is clean. The problem may lie further along the waste (too mant tight elbows, waste running uphill behind the unit or outside the house). How fast does the sink drain? I've never been a fan of pumping dishwasher or washing machine waste into the the sink trap. A seperate WM trap with stand pipe is the way to go..
    • Like Like x 1
  12. BobbyJoe

    BobbyJoe Member

    Thanks for the info and the kitchen sink doesn't drain fast, it is quite slow the water takes a bit of time to drain down the plughole. What is a trap and where is it located under the sink?
    I appreciate all the advice as once I know what needs to be done I will get a plumber out to fix as much as possible :)
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  13. Headrush

    Headrush New Member

    The trap is the part directly under the sink where your washing machine hose is connected. It's the first place to look for blockages from the sink..
    • Like Like x 1
  14. moonlight

    moonlight Plumber GSR

    I think you should get a professional to take a look, I don't think you are knowledgeable enough for the task at hand. You could be opening a can of worms for yourself. Good luck.
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  15. Ric2013

    Ric2013 Plumber

    I agree with Moonlight. Simply because it is really hard to see what is going on in your place without being there, and photographs are only so good. Yourself not being that knowledgeable makes it difficult to communicate what is going on, much as I admire your effort.

    As far as the rest is concerned, it really doesn't matter whether a washing machine valve turns right of left as long as it turns on and off, and the absence of servicing valves is only an inconvenience. So long as you have an effective way of shutting all your water down in the event of a burst pipe, I wouldn't worry. I don't always fit isolators on every tap, as it just adds to cost and environmental impact of the manufacture of parts.

    As long as your taps work efficiently, then leave them unless you don't like the look of them.

    A (trapped) upstand in the pipework for a washing machine is great and is what I would recommend if the waste pipework is beyond criticism, but if your waste pipe is slow to let water go away, or it gets blocked, then the likelihood is the upstand will overflow. Having experienced both, I'd rather have a sink filled up with washing machine water than a floor covered in it.

    Smells from the sink waste are probably water from the sink going into the washing machine - does the machine smell as well? Or if other drains (I assume you mean waste pipes from basins etc.), then the trap (the U bend) is not working properly probably due to poor plumbing downstream (or it needs removing and cleaning out) or it isn't the correct type.

    If you want to study part G of the building regulations to try to understand waste systems, it might help you, or it might do your head in trying to apply it to real-world situations and you'll realise why we study as plumbers, and why it's a lot to explain to you.

    I'd get in a plumber to ensure your kitchen waste pipe is run to a good standard and have it re-run if not. It may just be blocked with something like tile grout. If having it re-run, have it run in 2" pipe if it is sharing the sink and washing machine waste if practicable and affordable, or have a new dedicated washing machine waste run added. But whether these suggestions suit what you have in your house is not possible to say without being there and seeing what you have. Doing things to the nth degree is fine in some cases and totally impracticable and unaffordable in others. That's why I suggest finding a decent plumber who is good at problem-solving.

    I wish all my customers were like you and wanted to understand their systems.
    • Like Like x 1
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