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Vacuum Breaker Termination Height

TNEng21
TNEng21 Member Posts: 7
in Strictly Steam
New member, 1st post, look forward to many fact-filled discussions.

Scenario: (Commercial Application)

100% OA AHU (~20 kCFM), (3) vertically orientated steam distribution preheat coils (i.e.: supply/return headers @ bottom of coils) with dedicated F&T per coil and (1) modulating control valve (CV) serving preheat coil bank. Upstream of each F&T inlet, there is an elevated, horizontally oriented swing-check serving as a vacuum breaker (VB).

As a result of an airflow reduction years-ago, and years of differed PMs, one of the F&Ts and one of the VBs have failed.

This exercise will consist of appropriately sizing a new CV, F&Ts and replacing the swing-checks with actual VBs.

Here is my question: when installing the VBs, should they be piped to above the top of the coil? The current swing-checks are installed just below the elevation of the coil headers.

Any guidance/ direction provided would be greatly appreciated.

v/r
Dan

Comments

  • Intplm.
    Intplm. Member Posts: 2,338
    It would usually depend on the Vacuum Breaker and how the manufacturer suggest using it.

    What VB are you considering?
    TNEng21
  • Pumpguy
    Pumpguy Member Posts: 715
    As a general rule, the vacuum breaker's location doesn't really matter.

    So long as the internal pressure is lower than atmospheric, atmospheric pressure will push open the VB or swing check valve to equalize the pressure on either side.

    If there is liquid present above the VB, that liquid's head column could affect how the internal pressure balances out. In that case, put the VB above the expected liquid level so the pressure equalizes out to atmospheric.

    If equalizing time is a factor, research the CFM capacity of the VB. IME, VBs are somewhat specialized and have lower flow rates than an equivalent swing check valve.
    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.
    TNEng21
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 16,901
    I would put the VB or check valve above the top of the coil . I like putting them up high to keep them out of the water. Tunstall assoc. is a good source, but I usually just use a Y pattern check valve.
    TNEng21Intplm.
  • TNEng21
    TNEng21 Member Posts: 7
    Thank you for all the comments/ input. I'll be terminating the VBs above the coil. Thanks again.

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