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Stabilizing pressure on hydronic system.....JohnNY

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Brad White_9
Brad White_9 Member Posts: 2,440
Is the 23 psi a "net number" or does it allow some pressure cushion at the top, John?

Also, where have the leaks occurred? If near the top or appreciably above the basement, that is a worse situation given that you are not at 30 psi even at the bottom of the system. Seems you are bouncing up against your relief valve; is it weeping?

The type of tank matters less than the size. I suspect your tank size is too small by half. That is a lot of pressure for an incremental temperature increase. Imagine what it is from a cold start?

A larger tank would be more forgiving (more air cushion to compress). Also, if the tank could be moved to the attic/upper floor if any, it would not need to be so large or another way, would be more effective. Of course the connection point still has to be the PONPC and an express line run down to where the circulator is. As a trial run, you could install a diaphragm tank in parallel to the same point of connection and see the results. If it is a "go", then put in another one and get rid of the air type tank to eliminate that as a variable.

<u>Drastic Over-reacting Engineer Second Option Alert: </u>
This may not be an option but what the heck....Short of changing the radiators (leaking and not even at 30 psi), I would take a page out of the high-rise design book and install plate exchangers about halfway up (could fit in a closet) and feet up and down in two pressure zones. Sounds drastic I know but you are on the edge.

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  • JohnNY
    JohnNY Member Posts: 3,230
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    The problem:

    5-story home needs 23 psi to lift water to top of system.

    Cast-iron rads throughout only rated to handle 30 psi.
    Several leaks have already occured.

    Pressure rises 6 psi when water is heated from 140 to 175.

    Expansion tank is large vertical, non-diaphragm type.

    Could I get better control of my system pressure if I switch compression tanks to diaphragm type?



    Thanks in advance.





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  • Ken_40
    Ken_40 Member Posts: 1,320
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    Yes!

    And, why are you fooling with heating at this time?

    You should be at the restaurant looking at menus, searching the wine and beer lists, determining whether the cavatelli is as good as the manacotti, veal cordon bleu and whether or not Perotti draft beer comes in pitchers; the scampi is fresh and the scungilli tender.

    How can you ever think of work at a time like this? (;-o)

    The Big Ugly won't happen unless you make it happen!
  • JohnNY
    JohnNY Member Posts: 3,230
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    First of all..

    ...the cavatelli (fresh, made with potato) is much better than the manicotti, so we're going that route.

    Second of all, I'm only allowing for a 2 psi cushion at the top.
    The leaks on the CI baseboard sections were at the push nipples, and one sand hole mid-section, on the two lower floors.
    The commercial boiler is fitted with a 50psi relief valve.
    Now, I'm not an engineer, but I feel I don't like what I'm looking at with regard to the exp tank. It's vertical and probably holds about 20 gallons total. Looks like there's not enough air to squeeze.

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  • Brad White_9
    Brad White_9 Member Posts: 2,440
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    Oh heck, you nailed it, John

    That does seem like a small-ish tank for what I presume is a fairly large volume system. You are right on track.

    If you can get me the rough amount of pipe by size and a good guess at volume, I can come up with a good size for the expansion tank, rather than guessing. At least you have a 50 PSIG relief valve.

    I would still have to ask though, with a sand hole and leaking push nipples, are you still cutting it a little close? How do you get around that? Curious.
  • JohnNY
    JohnNY Member Posts: 3,230
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    Luckily....

    ....this is not my installation, I'm being paid as a one-time walk-through consultant. I do that from time to time. It's time consuming but easy money.

    What I'm likely to propose is to control the pressure fluctuation and swap out the radiation on the first two floors for a more suitable product.

    I'm not against fin tube when the situation calls for it.

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  • jackchips_2
    jackchips_2 Member Posts: 1,338
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    Sorry,

    no advice John, but two questions:

    1) Is this an older system and if yes,

    2) What has changed to cause the problems?

    These are the threads that we learn from, thanks to you and Brad.

    Jack
  • JohnNY
    JohnNY Member Posts: 3,230
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    New system

    Newly-renovated building converted from steam.
    This was the system's first season of use.

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  • uh ohhhh

    Uh ohhh, here comes Steamhead on this one.... Cast iron baseboards shud hold pressure up to 50 lbs when properly installed... Sand holes are factory defect, installing uneven pressure on push nipples are installers nightmares unless from factory...
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928
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    Same radiators used for the steam system and for the conversion?
  • Brad White_9
    Brad White_9 Member Posts: 2,440
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    I agree with Ray

    that the defects stand on their own and should be corrected. I would stick with cast iron though for all the right reasons. (No fin-tube especially in part and certainly not coupled to CI in the same zone as you know).

    It is a shame that it is new. Still need a bigger expansion tank though, I bet.
  • JohnNY
    JohnNY Member Posts: 3,230
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    The radiators..

    ... are new and from a manufacturer I've never heard of. (red flag #1?).
    I'm guessing cheap China imports.

    And I'm inclined not to blame a sand hole on 30 pounds of pressure either.

    As for mixing CI with other heat emitters, I believe it becomes less of an issue when using constant circulation as we are.

    No. There are no TRVs.

    I know.

    I know.




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  • Brad White_9
    Brad White_9 Member Posts: 2,440
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    I am with you on constant circulation

    but TRVs are, well, you know, you know :)

    I will have to give you a noogie when we meet a week from Friday.

    Brad
  • JohnNY
    JohnNY Member Posts: 3,230
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  • Ken_40
    Ken_40 Member Posts: 1,320
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    The wholesaler should eat...

    the leakers. If this was a one shot deal, the heating guy bought Chinese goods directly off the boat (for about 12-20 a piece) - he made enough cake off the rad markup, to be able to afford to go back and eat the labor!

    And here you thought buying the cheap stuff would allow real money-making profits on cheap goods... Now you have to eat the labor 'cause the fine print "where is; as is" - says ya' do.

    Been there, done that

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