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Rate of pressure loss

Discussion in 'Plumbing and Central Heating' started by whenisayjump, 15 Apr 2021.

  1. ianmcd

    ianmcd

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    I have no idea please tell me ?
     
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  3. fixitflav

    fixitflav

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    Because it was relevant to the estimate I made. It shows I do know the difference between gauge (barg) and absolute pressure (bara).
    BTW what would your estimate of volume for 0.1 bar pressure drop be?
     
  4. whenisayjump

    whenisayjump

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    It's a rough guess based on the dial that's on the boiler, essentially shorthand for it's dropping a 'little bit' each day.

    We have an external draincock that has a weep on one of the joins, the original question was to determine if that could be the reason for a small but noticeable daily loss of pressure.
     
  5. ianmcd

    ianmcd

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    well start with sorting that
     
  6. ianmcd

    ianmcd

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    without knowing barometric pressure, system volume and system temperature at each measurement I wouldnt have a clue, was the pump running at first measurement and at second measurement,is it a fixed rate pump ? is it an ERP pump, what was demanded on the system was HW and all zones open when taken, the answer is I havent a clue and neither do you
     
  7. Gorners

    Gorners

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    OP, why don’t you let some water out of a bleed vent into a measuring jug until you’ve lost approx. 0.1 bar. Might need someone at the boiler while you do it or a few trips back and forth. Only way you’re going to get a decent estimate on your own system with variables others have mentioned.
     
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  8. fixitflav

    fixitflav

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    You could try reading the OP's #18, I think we can give him credit for having the common sense to quote a typical figure over a few days, averaged over temperature variations. Do you really think variation in barometric pressure would make a significant difference? If the pressure vessel is close to the pump suction, as it should be, that fixes the minimum system pressure, and the pressure at the vessel connection varies very little whether or not the pump is running.
    I do have a clue. I was trying to help the OP by making an estimate as requested, it could only be a rough one, as I said, and obviously based on some assumptions. If he wants to do a test as Gorners suggested, I'd be interested, and if my estimate is a long way out I'll admit I was wrong.
     
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  10. ianmcd

    ianmcd

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    What does the vessel have to do with it ? please explain why some boiler models need to see a pressure differential once the pump has been powered before they will allow the boiler to fire , if a boiler expansion vessel is correctly charged and the communication is clear then it will never affect anything to do with the system pressure, the primary water temp will, as will the pump
     
  11. fixitflav

    fixitflav

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  12. fixitflav

    fixitflav

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    Certainly. Assuming the vessel connection is close to the pump suction, and is charged to say 1.5 barg, with cold system, that will be the pressure datum for the system. If the system pressure loss and hence the pump generated pressure are say 1 bar, when the pump starts the pressure at the suction stays at 1.5 barg. The pressure after the pump rises to 2.5 barg. The pressure falls round the system, back to 1.5 barg at the pump suction/vessel connection. There is a differential pressure across the boiler (and pump, and rads) any of which can be detected, if needed to allow boiler firing.
    Of course, the pressure rises as the system heats up and the water expands. If checking to see whether top-up is needed, clearly it's best to read pressure over a few days, when it's in the same state each time, preferably cold.
    Sorry, I don't think that makes sense. Please reword it.
     
  13. fixitflav

    fixitflav

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    Any developments on this?
     
  14. whenisayjump

    whenisayjump

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    No not yet, the company that installed the boiler were supposed to be coming on Friday to fix the draincock... but that didn't happen o_O
     
  15. fixitflav

    fixitflav

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    Did you do the Gorners test a la #21?
     
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