Low mains pressure and flow

Discussion in 'Plumbers' Talk' started by Mibazza, Jan 12, 2019.

  1. Mibazza

    Mibazza New Member

    Hi, I have low mains pressure and flow. It's above the minimum so water authority will do nothing. So I'm thinking of installing a break tank and booster pump. I have a digger, can I sink a 500l tank in my garden and cover it over? What would be the issues?
  2. Allsorts

    Allsorts Well-Known Member

    500 litres is a lot. Don't forget it'll be refilling al the time from the mains as you draw off water, so it should really run dry; 250l is more usual for a domestic situation.

    Anyhoo, what's your plan? Will this breaker tank be topped up by your current pitiful mains flow and then you pump out from that at the rate that you want? Or will it be filled and compressed by a pump on the mains side?

    Either way, it'll have to be a tank with a diaphragm inside to accommodate the changing volume - you obviously cannot have a water-contact air gap in there when it's for drinking water.

    It makes sense to me that a system where the tank is pressurised up to say 3bar (tho' 4.5 bar models are common too) and then you draw off the water at that 'stored' pressure is preferable as the pump won't be firing up on draw demand, and also water delivered by a pump just usually feels hellish - the whoooosh effect.

    Other issues? If it's underground, what about maintenance?

    Do you have a garage it could be located in instead? Or even room for a small shed like a bin store (it wouldn't have to be much over 2-odd feet square)?

    Check out the Grundfos Home Booster or the Challis CB+250. Other makes too. As a solution to poor mains flow and pressure, these WORK.
  3. KIAB

    KIAB Well-Known Member

    Have your neighbours also got low mains pressure problem?
  4. Severntrent

    Severntrent Member

    "you obviously cannot have a water-contact air gap in there when it's for drinking water".

    Interesting comment, concrete service reservoirs all have air gaps which can fluctuate several metres during a week
  5. Mibazza

    Mibazza New Member

    Well I'm not sure quite yet how the pressure will be built up. From what I understand, I cannot boost the mains water pressure directly and I want to have about 3 bar minimum for a megaflo cylinder and balanced pressure hot and cold. At the moment we have low pressure and flow and an old Mexico gas boiler with a vented hot water cylinder upstairs, but the property is flat roofed so the header tanks sit in the cupboard just above the hot water tank and both hot and cold pressures are rubbish. The cold taps are all mains fed, just header tanks for hot water cylinder and F&E on central heating. But we want to upgrade the house by upgrading all the rooms and decorating, and I fell now is the time to upgrade the water system before we start decorating. So I'm open to any and all ideas. If I can put a break tank above ground then I have plenty of room for this, 6 acres. But there is no garage or shed close to the house they are all quite remote. So it would have to be outside the house. I can easily build a shed to keep it in but would this be sufficient to stop it freezing in winter? It wouldn't have heating or insulation, but perhaps there are options for that on the tanks such as anti-frost trace heating and insulation? Also what about summer? Could the water heat warm enough through solar radiation to be a legionella or other bug risk? We want to have a large shower cabinet with luxury shower ie drencher head, normal head and possibly body jets as we had this in our old house and now we just have a 9kw electric shower in a pokey dark shower cubicle cut into a wall. We plan to stay in this house long term perhaps always so I want to get it right and put in the best system I can.
  6. Allsorts

    Allsorts Well-Known Member

    I'm referring to small domestic units of storage for potable water. I'm pretty sure I'm right but will happily be corrected.

    Mibazza goes away for a 2 week holiday and then quaffs a glass of air-stored water on his return. Deader than a dead thing.

    Ok, I exaggerate, but I am pretty sure I'm right about the potable water regs :)
  7. Allsorts

    Allsorts Well-Known Member

    Obviously the single best method is to improve the supply pipe to your property if this will have any effect; no addition devices required, no maintenance etc. But you have discounted this as an option as the WB won't do anything about it.

    The WB is only responsible for the mains supply up to your boundary stopcock, I understand. So, first question; what is the water pressure and flow like at the WB's side of your stopcock? If that is also pants, then there's no point in pursuing that any further. But if it's awesome, then the obvious solution is to dig your narrow trench and drop a new MDPE pipe in there. Jobbie should be jobbed.

    Failing that the next best option is to install a pumped accumulator and have that supply an unvented system - which is what you propose.

    You CAN pump the mains, but only up to 12 lpm - which is nothing like what you are after, so these accumulators work by having them filled at this max rate and pressurised up to 3 or 4.5 bar (the guy who did my bro's tiny flat fitted a 4.5 bar unit, and that nearly knocks him over in the shower...)

    As you said, if you build a purpose-made shed for this, insulate it well and fit a frost-stat and wee heater inside - jobbie jobbed. Summer Legionnaires won't be a problem 'cos the tank is sealed and not open to the air. It is effectively just 'a short length of very wide water pipe' :)

    Contact Challis and Grundfos and ask them everything you need to know - they are both very good at replying.

    These types of units WILL sort your problem - no question.
  8. Mibazza

    Mibazza New Member

    Well I'm doing a bit of research at the moment and I've seen all in one tanks with variable speed motors online like Grundfos (not sure if motor is variable speed) and Powertank. I reckon I could manage to fit one of these in a downstairs cupboard which would be reasonably easy to pipe to and from. So maybe indoors is a better option. I could manage to fit a 300ltr tank in the cupboard. I'd like the tank to be as big as possible as the flow rate is pretty low for filling back up and we like long lazy showers with lots of water (think tropical rain storm). Our water pipe comes off the mains a few hundred yards from our house as we are the only property at one side of a main road, the rest of the village is further down on the other side and I think the length from the main might be the reason for our poor pressure and flow. I know the pipe comes off way down the road as the previous owner recommended we insure it as he had issues before. Plus we lost water a few years ago when it was dug up by ground works further down the road near where it connects to the main and nobody else was affected.
  9. Mibazza

    Mibazza New Member

    Ok thanks for the reply's so far guys all good info. I think by the sound of it a break tank and pump is the way to go. I like the idea of a variable pump, sounds like I can set the pressure on this? Also like it as we often have two electric showers going at the same time in separate bathrooms so I think the variable can help smooth the load between the two new mixer showers? I guess when I get home from work in 10 days time I'll start surveying the pipe runs and autocad'ing the layout I think I'll need. At the moment the water comes in under the kitchen sink, I think it tee's here 22mm to rest of house and 15mm to the kitchen sink above it. Remarkably the kitchen sink is the worst tap in the house. It has always been slower than the rest and I'm not sure why. So I may just rip out all the plumbing from the incoming connection and start again as I'd have to pipe to the break tank, then out to all the outlets, hot water cylinder and new system boiler (to get rid of the old Ideal Mexico boiler and F&E tank)
  10. KIAB

    KIAB Well-Known Member

    That's what I want to know,if if mains pressure is good WB side, then I would also lay a new 25mm MDPE pipe to house.
    Seen it before with low mains pressure, boundary stopcock faulty & a lead pipe a fraction of it's proper internal size,once it been replace,water pressure was restored.

    And we don't know the distance involved from WB main to house.
    Last edited: Jan 12, 2019
  11. Mibazza

    Mibazza New Member

    WB main connection to my house is 250 yards along the edge of an A class road with other services such as electric, fibre optic, road drainage etc running alongside or crossing over/under as I have seen various companies out at the roadside digging down to install services for new houses at the other side of the road. So it's not as easy as me getting my shovel out and digging in my garden, this is rural and a long run so even with my own digger (which I have) I wouldn't be able to do this on my own. I wonder in that case if I can apply to have the pipe upgraded, but since they are supply the minimum pressure and flow I think I'm stuck with it.
  12. Allsorts

    Allsorts Well-Known Member

    If the issue is down to the poor mains pipe from your 'roadside' stopcock then a new 25mm pipe should sort it. 250m is quite a long run, so there's a chance that's the issue - but I don't know the calcs involved. You may be able to justify a wider pipe - say 32mm - but the WB won't do this for you (unless you pay them a shed-load) - from the SC to your house is your responsibility.

    But there is no point doing this if the WB's mains supply is pants - so you need to ask them. BUT, if the mains supply on the road is good, then a new pipe is the obvious and best solution.

    A 250m trench is not a biggie - why isn't that straightforward? Fit a super-narrow bucket and chop away :).

    Anyhoo, if you do have to go 'pressurised accumulator', then they are not that physically big, so an understairs cupboard sounds ideal. Get advice on the size - bear in mind that this store will be constantly replenished at 12lpm, so it ain't going to run dry unless you do summat strange. (And even if it does run dry, it'll still supply the house at 12lpm...)

    They will sort your issue. They will provide 'endless' water at 3 (or 4.5) bar pressure - that's more than enough for anything.

    (My bro ended up going Grundfos as the installer said that's the only unit he works with. But I'd investigated Challis beforehand, also speaking to the boss (called, er, Mr Challis...) and was impressed.)
    KIAB likes this.
  13. KIAB

    KIAB Well-Known Member

    Agree with above,if WB mains pressure is good,then lay a new mdpe mains,some WB's only allow a 25mm connections, other allow 32mm connection,which would give you a higher flow, the pipe needs to be down 750mm minimum depth,150mm width trench is ample to lay mains in.
    Allsorts likes this.
  14. Allsorts

    Allsorts Well-Known Member

    I do like it when KIAB agrees with me. :)

    Now, KIAB, about this Brexit malarkey... :rolleyes:
    KIAB likes this.
  15. KIAB

    KIAB Well-Known Member


    Bah humbug!:D

    Back to OP's water main, if it's lead pipe, you might find your WB will connect up your new pipe for free,under the Lead Replacement Scheme .
  16. Allsorts

    Allsorts Well-Known Member

    Yes, if it's lead and the home-owner replaces all theirs up to the boundary s/c, then the WB are obliged to do so on their side too. Certainly was the case down here.
  17. Mibazza

    Mibazza New Member

    It's not just a case of fitting a narrow bucket and chopping away. Over half of the pipe run is not on my land and is under the grass verge next to an A' class road. I'm pretty sure I can't just start chopping away at the verge, as 1. my digger is not licensed for being on the road. 2. there are other services running down there too, I can't just go hacking away with my digger. 3. I'm pretty sure I'd land myself in a whole lot of trouble. I know I can dig it up on my property but thats only the last 15m or so, the rest runs out beside the verge of the road.

    CJASENG New Member

    Which devices do you want the higher pressure and flow rate for? What's the current pressure?
  19. Mibazza

    Mibazza New Member

    The current static pressure is just over a bar and from memory the flow rate is about 8l/m but that was a while ago I tested it so I can't remember exactly. But we want to have good pressure and flow for mixer showers mainly. My plan is to replace the old Mexico boiler with a system boiler to elminate the F&E tank, a megaflo unvented to eleminate the feed tank for the cylinder and go all mains pressure. So I think about 3 bar and upward of 12l/m is required, but the more flow the better.

    CJASENG New Member

    I would go back to the mains water company, You should be able to get at LEAST 10l/min. The static pressure is only going to guarantee you get water to the top of your house. The Dynamic pressure your receiving is not enough to give you an adequate flow rate. It's a difficult one as I'm not sure there is a regulated 'minimum' flow rate they have to provide, it's more of a guideline. I would try to measure the dynamic pressure. I suspect the second you open a tap your dynamic pressure is falling right down. I believe they are supposed to 'maintain' 0.7 bar at all times. Bernoulli's equation and Q=AV tells me your going down to approx 0.0026 Bar for a flow rate of 8l/min on a 15mm pipe. In order to achieve 10l/min (in a 15mm pipe) you need about 0.0044 Bar.

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