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Thread: CO detection driving a solenoid valve

  1. #1
    Join Date
    Mar 2006
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    Boston, MA
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    660

    CO detection driving a solenoid valve

    I have a design challenge that perhaps some of you can help me with. I've got 4 CO detectors, connected into the FA system as Supervisory Signals. And if any one of these CO detectors goes off, I need to have a solenoid valve shut the gas off to the hoods in this area; this is a commercial kitchen.

    I wanted to have the Fire Alarm control Panel send that signal but am told that the Honeywell panel is not listed for control.

    Gameplan B is to operate the solenoid off an aux contact on the CO detectors. Now here's the thing, if I use N.O. aux contacts on all 4 CO detectors, wire them in parallel and then in series with a 24V source and the 24V solenoid, that works except that the system is not fail safe. i.e. if the power supply fails and/or there is an open circuit, then no one would know of the problem.

    I could wire N.C. aux contacts in series but then the solenoid valve would be constantly energized and that can't be good. So what is the best approach for a fail safe system?

    Thanks,

    Mike
    Mike Shields, PE
    Boston, MA

  2. #2
    Join Date
    Oct 2007
    Location
    New Jersey
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    1,391
    Quote Originally Posted by mshields View Post
    I have a design challenge that perhaps some of you can help me with. I've got 4 CO detectors, connected into the FA system as Supervisory Signals. And if any one of these CO detectors goes off, I need to have a solenoid valve shut the gas off to the hoods in this area; this is a commercial kitchen.

    I wanted to have the Fire Alarm control Panel send that signal but am told that the Honeywell panel is not listed for control.

    Gameplan B is to operate the solenoid off an aux contact on the CO detectors. Now here's the thing, if I use N.O. aux contacts on all 4 CO detectors, wire them in parallel and then in series with a 24V source and the 24V solenoid, that works except that the system is not fail safe. i.e. if the power supply fails and/or there is an open circuit, then no one would know of the problem.

    I could wire N.C. aux contacts in series but then the solenoid valve would be constantly energized and that can't be good. So what is the best approach for a fail safe system?

    Thanks,

    Mike
    Actually, I'm pretty sure that there are solenoids listed for 100% duty cycle. In fact, if the valve is listed with a manufacturer's suppression system I'd bet a reasonable sum that that's the case. Using a reset relay box, power is turned off when the system activates. The box keeps the valve from re-opening when the system is reset by requiring a separate button to be pushed.

  3. #3
    Join Date
    Nov 2007
    Location
    Louisville, KY
    Posts
    367
    Marcuco's CM-21A is designed for fan control, I'm not sure if it is listed for your application. It has a Form A relay to trip your alarm panel and a Form C relay that might be used to control your solenoid.

    You could use the normally closed contacts in series on multiple CM-21A to energize another relay all the time and de-energize on alarm to trip your solenoid. You could even add an end of line relay to monitor the power to that relay and trip a supervisory zone on your alarm panel if you lost power.

    http://multimedia.3m.com/mws/mediawe...-21AManual.pdf

  4. #4
    Join Date
    Feb 2003
    Location
    Portage, Indiana NEC: 2008
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    9,654
    I'm very much confused as to why you or someone would want to do this around open flame non-vented gas fired equipment? I can understand in a home for a furnace or water heater that is vented out, but a CO detector would almost always trip in a kitchen?

    I even had to ask my inspector why he required the CO detector to be in a hallway next to the furnace room, because if the fire box ever goes bad the fumes are not going to accumulate in the hallway, they are going to be blown through the ducts to each room, true if the flue to the outside is blocked or negative pressure is the cause then having one in the hall will be the best place, but most co poisonings are caused by a bad fire box, or in the case of a commercial kitchen negative pressure cause by not enough makeup air.

    While the circuit would not be hard to do this, I see allot of trouble down the line especially if the burners are fired up before the exhaust hood is.

    For fail safe the gas valve would almost have to be continuous duty, and powered through a N.O. contact, but power failures and breaker tripping are going to be a nightmare for the operators of this kitchen, not even including the fact every time they fail to start the hood up first will cause false alarms, and any pilots would have to be re-lit after every trip.:confused:
    Last edited by hurk27; 05-26-11 at 05:44 PM.
    Wayne A. From: N.W.Indiana
    Be Fair, Be Safe
    Just don't be fairly safe

  5. #5
    Join Date
    Apr 2008
    Location
    Ann Arbor, Michigan
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    4,452
    110526-2009 EDT

    A standard gas furnace valve is manually set to ON and maintained on by a thermocouple signal. This valve is also going to be gas rated, and are extremely reliable.

    If there are issues with rating then you could use the thermocouple connected to the valve and have your control circuit power a resistor to heat the thermocouple. I would prefer the direct powering of the valve coil.

    So you could supply a holding signal to the thermocouple input instead of the thermocouple. Loss of power to whatever circuit provides the holding current will cause the value to close.

    I have never experimented with one of these values, but I expect there is a substantial differential between holding and pull-in. In fact the coil may not tolerate a current level that would pull-in the valve without the manual assistance.

    .

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