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12 Story 1920's Building Water Hammer localized to 2 units.

Hi, This is a tough problem. The incoming steam pressure is 150, seattle steam. There is a Belimo back pressure valve controlled by Pressuretrol. The process steam is 2 psi. It was an old VariVac system that is now running on constant vacuum since the 80's. In the last year two units have bad water hammer in the supply line. You can hear the steam pushing lots of water. The traps are working and are regularly replaced. The main air vent (That I am aware of) is operating.



The vacuum also supplies vacuum to a HX for hot water, and it is running at 5 PSI steam on Fisher regulator.



The vacuum dumps the condensate into a PREHEAT hx, shell and tube, and then to the flash tank which now simply drains to hole in ground.



The system is on a setback, night time only, for 13 hours, and operates 3-4 cycles a night.



However anytime the system cycles, the water hammer occurs.



The radiators in question are Column style, and I am under the impression it is a Down feed system for all but the top two floors. The unit with the issues is on a downfeed line however, at least that is what I am finding out. These are on thermostatic operators, danfoss I believe.



There are no prints.



I lowered the pressure today to see if less pressure would alleviate some of the issues, before its too cold and I get complaints.



Any help or insight would be wonderful.



The main steam trap on the main header appears to operate correctly and it is also connected to the vacuum pump.



Vacuum pump provides 7 pounds of vacuum. And when the steam is energized it operates around 10.



Thank you,



Timothy

Comments

  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,471
    edited October 2012
    double post deleted

  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,471
    Knocking in Seattle

    Do I understand that the pressure goes from negative 7 to positive 10 psi?

    When you lower the pressure, what complaints do you get?

    Most traps have trouble with pressures over 3psi, and become paperweights.--NBC
  • Mechanicaltimi
    Mechanicaltimi Member Posts: 4
    RE: Knocking in Seattle

    It was near 5 today and I adjusted to 2. But I am hoping less dense steam will encompass the building faster, and reach the radiators faster.



    There were only noise complaints in 2 units. However I am quickly learning that some people just dont formally complan.



    I could hear the water in the supply piping gurgling. I wanted to look at the supply piping but it is in the walls and so taking out walls is last resort.



    I can only find one vent for air. As far as I know all of the risers have traps on the bottom, and as far as I know they are on a vacuum system.
  • Mechanicaltimi
    Mechanicaltimi Member Posts: 4
    RE: Knocking in Seattle

    It was near 5 today and I adjusted to 2. But I am hoping less dense steam will encompass the building faster, and reach the radiators faster.



    There were only noise complaints in 2 units. However I am quickly learning that some people just dont formally complan.



    I could hear the water in the supply piping gurgling. I wanted to look at the supply piping but it is in the walls and so taking out walls is last resort.



    I can only find one vent for air. As far as I know all of the risers have traps on the bottom, and as far as I know they are on a vacuum system.
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,471
    Some information

    http://www.heatinghelp.com/files/articles/1991/varivac2180.pdf

    There is more here as well if you do a search.

    There is probably a manual available with specific diagnostic procedures.

    The system seems to use traps designed for vaccuum. Were your traps correctly chosen when replaced?--NBC
  • icesailor
    icesailor Member Posts: 7,265
    What changed?

    Adding to what NBC said, my #1 rule of troubleshooting is this. If it worked for 50 years (or add any number) and it worked well, what changed to cause the problem. Knowing what I know about "experts" that some of us follow behind, someone may have not known the difference between pressure and vacuum, and replaced traps or trap parts with the wrong parts. It MUST have worked when it was new. Why does it not work properly now? Did someone install some incompatible equipment somewhere in the building and someone else changes things to try to make the incompatible equipment work?

    It is my experience that problems like what you describe have a really simple and basic cause of their problems. Often, so simple that it is overlooked as being too stupid to look into. Well, the stupid person that screwed it up isn't as smart as you. So, put on your smart hat and pants and go at it.

    Anyone can install it and screw it up. It takes smarts and skills to find the problem and fix it. And it is fun and interesting.
  • Mechanicaltimi
    Mechanicaltimi Member Posts: 4
    Ok fine I am still troubleshooting.

    Yes, it hasn't worked properly for a long time, several years. They recently installed Tekmar 297 and it cycles in the night, used to be on a timer. So now it also cycles, because the tekmar. But, the problem existed 20 years ago, pipes that cracked were replaced a few years back.



    I have no complaints on lower steam pressure. However I want to solve it. I'll post the stupid answer once I have my smart hat on right =).
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