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More oil in tank (+80L) after new tank installed - why?

Discussion in 'Plumbing and Central Heating' started by snapd, 11 Dec 2020.

  1. snapd

    snapd

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    I had a new oil tank installed recently by an OFTEC-registered company

    Both tanks are the same, but the new one is 1100L capacity versus the old one being 1300L. They are both the same height and fitted with Atkinson Tankmasters.

    Since having oil, for the last five years, at least every fortnight I've measured the level on the Atkinson Tankmaster sight tube and made a note of it to see how much oil I had left.

    I calculate the amount of oil I have left as: (position on sight tube / height of tank) * tank capacity

    So for the old tank: amount of oil = (position on sight tube / height of tank) * 1300

    And for the new tank: amount of oil = (position on sight tube / height of tank) * 1100

    Before the new tank was installed, I measured the amount of oil I had left in the old 1300L tank and it was 132.47 litres. Once the new 1100L tank was installed, and after running it for around an hour to test the boiler was still working, I measured the level in the new tank and I had 210.87 litres.

    So somehow between tanks being installed I gained almost 80 litres of oil!

    I'm trying to think about how this could happen. I can only think of three reasons:

    1) There was already oil in the temporary tank and this was transferred into my new tank along with my old oil
    2) The level in the old Atkinson Tankmaster sight tube was incorrect at least every fortnight when I measured it for five years (I know the level in the new one is correct, as I dipped a cane in the tank to measure the level and compare it - I never did this with the old one)
    3) There is something within the tank which is artificially raising the level

    The installer politely suggested I had been measuring it incorrectly before. I can understand why he would think this, he's the expert and he didn't observe me measuring it each time. However, I know I was definitely measuring it correctly as I would do it before and after each delivery and each time I could see, for example, 500 litres had been delivered.

    Does anyone who knows more about this kind of thing have any theories on what could have happened for me to gain an extra 80 litres of oil during a tank installation?
     
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  3. snapd

    snapd

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    The only other difference between the tanks is the new one has a float valve and the old one does not
     
  4. lostinthelight

    lostinthelight

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    Are the sides on the tank absolutely parallel on all four sides, if not the amount of fall in the sight tube will vary at different levels in relation to litres used.
     
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  5. just pumps

    just pumps

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    Don`t mix up outside height with internal capacity.
     
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  6. oilhead

    oilhead

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    Tell us which tanks you had/have and we may be able to solve the problem. My guess there is some internal moulding on the new tank to add strength, which reduces the apparent capacity.
     
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  7. Hugh Jaleak

    Hugh Jaleak

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    New tank 1100L against old tank capacity of 1300L, but both the same height? I'd hazard a guess the new tank is bunded internally, meaning the bottom of the internal tank is higher, hence raising the height of the contents.
     
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  9. snapd

    snapd

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    Sorry, I missed an important detail.

    They're both single skin steel tanks.

    Although I can't find the exact tank I have online, if you look at something like https://www.tanksforeverything.co.u...e-Single-Skin-Steel-Heating-Oil-Tank-SIS.1350 (a 1350L) and https://www.tanksforeverything.co.u...Oil-Tank-SIS.1100-1100-Litre-Single-Skin-Tank (a 1100L) you'll note that they are of the same height and width but the 1350 is just longer. I believe this is the same with my new 1100L versus my old 1300L. I can't be sure that the steel is of the same thickness because I never measured it in the old tank, but I think it would have to be substantially different, implausibly so, to produce such a different measurement.

    My main concern is this: My understanding is they filtered my oil when they transferred it from my old tank to the temporary tank. But what if the additional ~80L is in the form of water or something else which was already in the temporary tank? My boiler is working fine. Would it be working if ~80L of water or something else was added to 132L of oil?
     
  10. oilhead

    oilhead

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  11. bernardgreen

    bernardgreen

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    Because the new tank is shorter the volume of oil per index on the sight tube will be less than it was in the old tank.

    A given volume of oil in the old tank covered a certain length of the sight tube. The same volume of oil in the new shorter tank will cover a longer length of the sight tube
     
  12. snapd

    snapd

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    I adjust for that by multiplying by the capacity of the tank, though.
     
  13. bernardgreen

    bernardgreen

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    The adjustment has to be based on the change in length of the tank ( assuming the new tank's width is the same as the old tank's width )
     
  14. Terrywookfit

    Terrywookfit

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    The C S A of the tanks must be different to accommodate the additional 200 litres.

    As b g has said.
     
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