Hot Water Cylinder Indentations !

Discussion in 'Plumbers' Talk' started by MarkyBoy, Jan 7, 2005.

  1. doitall

    doitall New Member

    First i would tie a bucket of water over the vent and turn everthing on ( keeping a very close eye on things) to see if water is being suck out.

    Secondly I would doubt that the cylinder imploding would take the insulation with it ( but thats a guess )

    Then I would check the open vent by blasting it with the cold mains and the cold feed turned off, at best if anything comes out other than water.

    Obviously there are risks involved and would best be tested with 2 persons and a lot of care
     
  2. doitall

    doitall New Member

    Is it possible I've got a dodgy cylinder (with a
    dodgy probe thermostat) ! :)

    Is this the right thread MB
     
  3. bathstyle

    bathstyle Active Member

    I still reckon the cold feed should be bigger.
     
  4. doitall

    doitall New Member

    I still reckon the cold feed should be bigger.

    No arguments from me :)

    When fitting a pair of 3bar mosoons I always install a 35mm cold feed
     
  5. MarkyBoy

    MarkyBoy Member

    Rather than a bucket of cold water, I could just turn the shower on and then go up into the loft and put my hand over the end of the vent pipe as I'd be able to feel it sucking.

    I wasn't convinced that an imploding copper wall would take the insulation with it either. There are no signe of cracking or breaking-up of the insulation at all.

    I'll connect the washing machine cold feed to the hot feed and blast the vent with cold water that way.

    The cylinder has a 22mm male compression inlet so would increasing the feed pipe to 28mm make any difference ?

    I also thought that if a cylinder started to implode it would do so in one specific place (a weak spot where the wall was thinner) rather than in small patches in different places.
     
  6. doitall

    doitall New Member

    Perhaps juniors been using it as a punchbag
     
  7. bathstyle

    bathstyle Active Member

    You cant increase the size to 28mm when you've got a com fitting- it wouldn't be worth it
     
  8. doitall

    doitall New Member

    You cant increase the size to 28mm when you've got a
    com fitting- it wouldn't be worth it

    Why ?

    Reducing it at the fitting would not effect the increase volume.

    We quite often reduce through the pump or valves then return to the larger size.

    As an example the 54mm primaries I'm installing at the moment reduce to 28mm at the flowshare valve then increase to 42mm connections at the cylinder, the by-pass is 28mm back to a common 42mm return from the 2 cylinders then connect into the 54mm primary return
     
  9. doitall

    doitall New Member

    Thought of a better way to explain.

    Gas pipe is too long for 22mm so you increase the size too 28mm, then you reduce it too 22mm or 15mm for the boiler connection.
     
  10. bathstyle

    bathstyle Active Member

    Night Doitall!

    I can't compete with your wealth of knowledge!
     
  11. bathstyle

    bathstyle Active Member

    Makes sense.
     
  12. doitall

    doitall New Member

    Don't believe you.

    I probably just been at it longer (46years)

    good night. :)
     
  13. bathstyle

    bathstyle Active Member

    Well i've been in this game for 12... so there!

    See you later my friend
     
  14. MarkyBoy

    MarkyBoy Member

    I blasted 30 seconds worth of mains cold water into the hot water system (via the hot feed to the washing machine)then turned on a hot tap. The flow rate of hot water was as normal so the mains cold burst must have escaped into the cold storage cistern via the expansion pipe. Also, I forgot to mention that I drained-down the cylinder yesterday afternoon (via the drain-off on the cold feed) and the cylinder drained perfectly. Can I therefore asume that the vent pipe is definetly not blocked ?

    I have measured the high point of one of the indentations (5.5mm) and so will monitor it for and additional movement. I'm not sure what else I can do.

    If the indentations are/were caused by slight implosions within the tank lining, will the water pressure within the tank push them back out again over time (assuming that whatever caused it doesn't happen again) ?

    Thankyou for all the help and advice.
     
  15. bathstyle

    bathstyle Active Member

    Try shutting cold feed to cyl then opening hot tap and blowing down vent or blowing through hot tap.

    Or even blasting with mains like you did before but with cold feed shut.

    Is the cyl full now? have the indents gone? I would contact albion and say you are worried about this problem. If they think it could be a manufacturing defect they'll bend over backwards to help.
     
  16. MarkyBoy

    MarkyBoy Member

    Thankyou Bystyle. I shut down the cold feed to the cylinder and repeated the mains cold feed blast excercise. The vent is definetly not blocked.

    The cylinder is full and the indentations are still there.

    I'm going to call Albion first thing Monday morning and report it as a faulty cylinder as I can't think what else it could be.
     
  17. doitall

    doitall New Member

    As I said earlier are you sure its not just someone playing about.

    pushing your knee into the lagging will make the indentation you discribe.

    just a thought
     
  18. MarkyBoy

    MarkyBoy Member

    No Doitall, I wish it was somebody winding me up. If somebody had pushed something into the lagging to make the indentations then the lagging would be cracked at the edges at least. But the lagging on all the indentations is completely smooth.
     
  19. Stoday

    Stoday New Member

    I probably just been at it longer (46years)
    Well i've been in this game for 12

    52 years experience between you and you still don’t know how a vented HW system works. At the rate you’re going, you never will.

    “Stick your thumb over the vent pipe & see if it sucks”. If you’ve turned off the cold feed and opened a tap, believe me, it will suck. With, say, a 10ft head, that’s 5 psi. The surface area of a typical HW cylinder is 1000 sq ins, so you would finish up with 2 ½ tonnes of compression on the cylinder. That’ll put more than a dent in it, it’ll crush it.

    “Block the vent, turn off the cold feed & put mains pressure on it”. That’ll press out dents. And if you’re very lucky and the mains pressure is low, the cylinder won’t rupture as well.

    When the HW system is operating normally, with no taps open, water will flow up the vent pipe until it reaches the same level as the water in the feed cistern. Open a tap and the water in the vent pipe falls below the cistern level until the height difference is equal to the head loss of the water flowing down the cold feed to the cylinder. You can pump the water out, in which case the water in the vent pipe falls further. As more water flows through the cold feed, its head loss increases. The pressure in the top of the cylinder is the height to the level of water in the vent pipe.

    If you try to pump more water out than the cold feed can supply, the vent pipe empties and the level of water in the cylinder falls to the HW pump supply connection and you start to pump air with the water. At this point, the pressure in the cylinder cannot become negative because it is open to the atmosphere via the open vent pipe. No matter how hard you pump, you cannot create a negative pressure (the pump can’t suck enough air).

    Under normal operation, some of the water in the vent pipe is replaced every time you open a tap and convection currents make sure more fresh water mixes in. This is as well, because if the water in the pipe were stagnant, you could get a build-up of bacteria.
     
  20. bathstyle

    bathstyle Active Member

    'Block the vent, turn off the cold feed & put mains pressure on it'

    Who said anything about blocking up the vent?

    The responses that Doitall, Markyboy and I discussed were instant, it was a form of fault finding to try and get the problem sorted.

    You have been off done your research and then come back......well done I take my hat off to you.

    You've certainly got a way with words Stoday.
     

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