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  1. #1
    Join Date
    Jul 2006
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    North Jersey
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    129

    Pneumatic guys - Diverting and Reversing Relay ??s

    Took over a building with some pneumatic VAVs, and found a bunch of these 'Diverting Relays' and some 'Reversing Relays' as well.

    Not sure exactly what these do, or how they work...Did a web search, but didn't find much info.

    Anyone know what these are all about?

    Thanks.
    MJB
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    I like turbos

  2. #2
    Join Date
    Jul 2000
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    Dallas,Texas
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    4,948
    Names differ, even by brand.
    A diverting relay could be a pressure selector relay. 2 different input pressure sources, 1 output. The control will control either the higher signal or the lower signal depending on which control is installed.
    A reversing relay may have 1 input, 1 output, and main air. As the input presure changes the output pressure changes in direct opposite proportion.
    Give us the number off that control and somebody will ID for you.

  3. #3
    Join Date
    Jan 2007
    Location
    Milwaukee Wisconsin
    Posts
    984
    Also could be a biasing relay (like a pilot positioner). Robertshaw/ Siebe i think, need #s.

  4. #4
    Join Date
    Jul 2006
    Location
    North Jersey
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    129
    Quote Originally Posted by wolfdog View Post
    Names differ, even by brand.
    A diverting relay could be a pressure selector relay. 2 different input pressure sources, 1 output. The control will control either the higher signal or the lower signal depending on which control is installed.
    A reversing relay may have 1 input, 1 output, and main air. As the input presure changes the output pressure changes in direct opposite proportion.
    Give us the number off that control and somebody will ID for you.
    That sounds like you're on the right track. I believe this building used to have two different pressures depending on if it were heating or cooling. Found two separate regulators tied into the old abandoned TAC control system (The building has new McQuays with BACNet control now).

    I'm gathering that when the unit was set to 'heat' that it would switch to the lower pressure so that the VAVs would 'know' it was in the heating mode and to basically switch functions.

    I'll get the #s off the controllers...We've seen two different types...Small black ones with a KMC tag on it...and these larger tan ones. Some say 'reversing relay' others say 'diverting relay'....

    Would love to switch some of these out to DDC so I can get some control over the areas.
    I like turbos

  5. #5
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    Dallas,Texas
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  6. #6
    Join Date
    Sep 2006
    Location
    Alaska
    Posts
    458

    Diverting Relays

    Diverting relays were often used to accomplish a complex task. The example I remember best is a fire alarm interface to pneumatics. When an area had a fire alarm the vav's could be set to shut down or open all the way to ventilate an area.

    Reversing relays were usually used to allow one controller to operate devices with different actions.

    For example you have a reverse acting thermostat controlling a normally open VAV box with a reversing relay to reverse the signal to a normally open reheat valve.
    Law Of The Thermostat: He who has the thermostat wins!!!!!

  7. #7
    Join Date
    Jan 2008
    Location
    windy city
    Posts
    4,426
    Quote Originally Posted by turbo50mike View Post
    Took over a building with some pneumatic VAVs, and found a bunch of these 'Diverting Relays' and some 'Reversing Relays' as well.

    Not sure exactly what these do, or how they work...Did a web search, but didn't find much info.

    Anyone know what these are all about?

    Thanks.
    MJB
    looks like a robertshaw. will need # to tell you what it is and how it works.
    \m/
    original member of the racoon brotherhood

  8. #8
    Join Date
    Feb 2010
    Location
    Cal
    Posts
    1,596
    Is that wireflex on the box inlet? I hope you like correcting duct issues as much as turbo's mike.

  9. #9
    Join Date
    Jul 2007
    Location
    Delta BC Canada
    Posts
    87

  10. #10
    Join Date
    Jul 2001
    Location
    Canada
    Posts
    1,807
    looks to be a R503-3 ROBERTSHAW diverting relay ( most werre made by KMC ) its SPDT non adjustable.
    Newer part was # R403-3 for Robertshaw and now TAC 2353-503

    http://www2.tac.com/data/internal/da.../F_24550_1.pdf

  11. #11
    Join Date
    Mar 2010
    Posts
    32
    single duct w/ reheats or double duct? large tan ones sound like kreuter static pres controls. whats the action of the stats?

  12. #12
    Join Date
    Jul 2001
    Location
    Canada
    Posts
    1,807
    Large TAN one as in his picture is the RS R503 diverting relay and not static pressure.

  13. #13
    Join Date
    Mar 2010
    Posts
    32
    your right c man that's a 503 didn't notice picture last night.

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