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Too much vac in entire system?

HVACRTEK83
HVACRTEK83 Member Posts: 5
in Strictly Steam

So I'm new to posting here but have been reading posts for years on here. Alot of smart guys here. I have recently started working for a school built in 1952 2 pipe steam, trane convectors in original parts of building, 18 ahus with hw coils fed from hx's that were not part of the original design. 2 unilux zf 600 ls boilers nat gas, 6 million+ btus input each. I have another post about drafting issues with these boilers but this is about excessive vacuum in both supply and return in system that happens quickly upon boiler shutdown. Condensate takes long time to get back to boiler room. So it's all dry returns that collect into a receiver,which then pumps into a feed tank. I'm wondering if this used to be a vacuum system and they put in a standard condensate receiver at some point not knowing, and now there's these issues. Why would I have vac in returns immediately after shutdown when there's an 1 1/2" vent up through roof from receiver. I thought maybe vent was partially plugged and I'm not done looking into that but I accessed the original prints from 1952 and the receiver is on there. It says it was a 20c American Hydrovac condensate unit. For 20k edr. Which the building probly has double that edr now, I'm working on calculating but it's not an easy task in this building. Anyone ever hear of American hydrovac? I can't find any info on this company. All that pulls up is a company that has wetvac trucks that come clean up job sites in Texas I believe it was. If this was supposed to have a vac condensate unit, how can I find out? The returns do seem kinda small so it almost makes sense it would have been. I don't have any experience in the design part of large buildings is why I'm questioning this, if anyone has any recommendations on what I should be looking into I'm all for it and appreciate any advice

Comments

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 17,798

    Never heard of American Hydrovac but that name suggests a vacuum pump to me. Maybe you can PM @Pumpguy he may know.

    I suppose you could always put a vacuum breaker(s) on the system.

    You need a pressure difference to allow the condensate to move. Either with a vacuum pump or allowing air into the system to allow water to flow

  • mattmia2
    mattmia2 Member Posts: 12,763

    Or a way to equalize the supply and the return.

    Seems like you would want the boiler to modulate or be staged rather than shut down on a system that size.

  • Steamhead
    Steamhead Member Posts: 17,789

    @Pumpguy might know, hopefully he'll see this and chime in.

    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
    mattmia2
  • mattmia2
    mattmia2 Member Posts: 12,763

    definitely a put your hands in your pockets until you figure out how it was supposed to work originally and if whoever added the new stuff did it in such a way that it can still function that way

    neilc
  • Pumpguy
    Pumpguy Member Posts: 751

    Equalizer lines?

    Your symptoms sound like a classic case of induced vacuum due to the condensing steam.

    Check to see if your system has equalizer lines. A 2 pipe system should have at least one. Most use a dropped water sealed check valve, although a 3/4" thermostatic steam trap will work just as well.

    If your system has the water sealed check valve, the clapper may be stuck on its seat. A few raps with a hammer should jar it loose.

    The attached file shows the details.

    equalizer lines.pdf
    Dennis Pataki. Former Service Manager and Heating Pump Product Manager for Nash Engineering Company. Phone: 1-888 853 9963
    Website: www.nashjenningspumps.com

    The first step in solving any problem is TO IDENTIFY THE PROBLEM.

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