Poor Pressure from a Megaflow Unvented Cylinder CL250

Discussion in 'Plumbing and Central Heating' started by thunderstarter, 23 Jul 2006.

  1. thunderstarter

    thunderstarter

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    Ive posted about this problem before, but we are getting no where with the problem and Im getting conflicting advice from Plumbers.

    To briefly describe our problem:

    We have a Megaflow CL250 Cylinder sited in our cellar (its an old victorian House) The cyclinder has good incoming pressure of 5 Bar (plus). This was achieved at great expense by moling a MDPE Main under the garden, in order to get rid of the old Lead Main.

    The Main is t'eed as it enters the property in the cellar. 1 way goes to a PRV currently set to 3 bar and feeds the cold supply in the house and the other T is the main supply to the Megaflow. (with a large bore plastic pipe of 28mm.) This supply then goes through the factory supplied PRV that comes with the Megaflow (with the built in strainer.) Which says it is factory set to 3 Bar. Without fitting a dial gauge onto the pipe run from the PRV to the cylinder its impossible to say what the incoming mains pressure is, but it should be 3 bar, reduced from the incoming pressure of 5 bar shouldnt it?

    The outlet from the top of the Megaflow is the standard 22mm.

    The resulting pressure in the whole of the house is poor to say the least. We had a plumber measure the Hot Water flow rate at 13 litres per minute (which is poor is it not?) The balanced cold water flow rate is identical.

    The Kitchen Hot Water flow rate (which is a short run from the cylinder in the cellar to the kitchen above) is 13 litres per minute and the outlet in the bathroom on the next floor above this is also 13 litres per minute (which kills any theory that long pipe runs with bends etc are causing a loss in pressure.)

    Can anyone advise of any other possible causes? Im really pulling my hair out on this one. Thanks for any help.
     
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  3. oilman

    oilman

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    13 l/min may not be bees-knees stuff, but it's not that bad. Since you're getting the same flow rate from all the taps, it must indicate the incoming main is the limiting factor.

    Turn on all the taps at once, and measure the flow from each of them, and add the figures together.

    You should know the static pressure because if you have had a plumber round he should hjave measured it. If he didn't/couldn't did you make a note of the breed of horse he was riding?
     
  4. thunderstarter

    thunderstarter

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    thanks for the reply Oilman.

    Could you explain though why Heatrae Sadia state on their spec on the website that the Megaflow operates on a minimum of 20 litres/per/minute (1.5 Bar) incoming....

    why should the outgoing from the Megaflow be only 13 litres/per/minute when the incoming pressure is 5 bar?


    This is from the Heatrae Sadia Website:

    Minimum Water Supply Reqmnts:
    20 litres per minute flow and 1.5 bar pressure. (At lesser values, the unit will operate but outlet flow rates may be unacceptable, especially with multiple draw-offs.)
    Please contact our Specification Advice Team to discuss specific site conditions if the above minimum requirement cannot be met. Tel: 01603 420220.
     
  5. ChrisR

    ChrisR

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    If the hot flow were limited by the incoming mains, you would still expect good flow when you turn the hot tap on, because tof the effect of the ppocket of air in the megaflo . The flow would desrease over minutes as the air pocket expands. For furhter info on that, if you are made of strong stuff, do a search on megaflo and see a recent mammoth thread.

    Have you checked the M'flo strainer? Also strainers on the taps. Sometimes disturbances send a bunch of grot through.

    I'd want to see dynamic pressure readings taken through the house - a gauge is only about £12.
     
  6. chrishutt

    chrishutt

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    You don't say what size the new MDPE supply pipe is (25mm, 32mm?). Also is the new MDPE pipe only replacing the old lead pipe on your property or does it extend all the way to the mains? It sounds to me as if you still have a flow restriction between your new pipes and the mains. As ChrisR says, you need to check dynamic pressures (when 13 litres/min is flowing) - it won't be anything like 5 bar!
     
  7. Agile

    Agile

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    There are a few unknowns!

    Firstly to Owner only just understands the difference between flow and pressure.

    Secondly, how long has the Magaflow been fitted for and is this a new problem or has it always been like that?

    13 li/min is not that bad if the taps are the dreadful high pressure Italian joystick type. They are designed for a mains pressure of about 4 bar.

    As Chris says you need to monitor the pressure from the mains at the entry point to the house.

    Another point is that the small 3/4" PRVs dont have a terribly good flow characteristic. Perhaps thats your problem.

    Your whole system is designed for a flow of say 20 li/min and you seem to expect to get that from each tap.

    Tony
     
  8. Softus

    Softus

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    I'm curious thunderstarter - what was your previous user name?
     
  9. simond

    simond

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    Assuming that you have tried;

    Clearing the strainer
    Making sure all the stopcocks are wide open and functioning
    And measuring the flow rate from a garden tap at 13 litres

    Then it is likely that your incoming flow rate is 13 litres per minute. This is not very good and is no justification for fitting an unvented cylinder. Like Heatrae Sadia say, to benefit from your investment >20 litres is required.

    The static pressure is good but it is the flow rate that primarily determines usability. Your installer should have checked both pressure and flow prior to fitting the unit.

    I suggest your first redress should be in this direction. If you asked him to fit this product, I guess he may have an excuse, although only a small one.

    Based upon the information given, this problem can be solved with an accumulator, although the age of the Megaflo will be an issue if you fit a GAH unit. As Chris R says, if you have a day to spare and a strong constitution there is a thread elsewhere.
     
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  11. chrishutt

    chrishutt

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    It's here.
     
  12. thunderstarter

    thunderstarter

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    thanks for all the replies guys....

    where do I start?

    Sorry, I posted on another forum (previously) and forgot to delete the bit about posting before on here (I dont have a previous user name on this forum.)

    I will check all the things that people have mentioned, ie, cleaning out the strainer and report back.

    Can anyone recommend a plumber in Huddersfield, who has unvented systems experience?

    Thanks
    Dan
     
  13. thunderstarter

    thunderstarter

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    also the problem has always been there since the Megaflo was installed. Its now got to a point where we are installing a main master bathroom and really we didnt spend all that money (which must amount to about 4k) installing a new main and unvented system, to get a cr*p pressure shower.

    We really need to do something about it.
     
  14. doitall

    doitall

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    You don't need an unvented man, just a plumber to sort the mains out. :LOL:
     
  15. ChrisR

    ChrisR

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    You said you have a 3 bar prv on the cold supply, and also that you have measured the balanced cold flow. Where/how did you measure that?
    They were both 13l/min?
    Flow at garden tap?
    You can suss out broadly where the restriction is by knowing the pipe route, and measuring flows. For example, if the restriction is mainly the taps , one tap won't affect another, but if it's the pipe, one tap will affect another becasue all the flow is going through the one restriction and being shared.
     
  16. bentheplumber

    bentheplumber

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    You say that you have only 13 l/min at the taps. What is the flow rate before entering the megaflow? It should be between 20 and 25 l/min. If it is below 20 then that will most likely be your problem. Remember high pressure is not the same as high flow. Just because the pipes are large will it automatically mean that the flow is going to be okay. Have it checked out
     
  17. steve32

    steve32

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    Is 5bar working or standing pressure.
    If its standing you need to check working pressure on an unbalanced cold supply without non return valve fitted.
    Take readings at diffrent times on diffrent days with one tap and then two taps running on half flow and record and take an avarage
    do the same on hot repeat for L/min
    13-15L is avarage for most megaflows that i work on in your type of house.
    When the water mains was replaced was it replaced to mains by water co or connected to your old supply and was external stop valve replaced.
    The supply in my area is 11-13L/min with a working pressure of 1.75-2bar.
     
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