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Thread: Any time delay relay experts here (Ideally with boiler knowledge)?

  1. #21
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    the switches are mntd external to the boiler
    example https://media.statesupply.com/filema...structions.pdf

    you can put orifaces, snubbers, etc to dampen any level 'noise'
    the delta is usually small, like 2" range

    an expert needs consulted
    the consequences could be dire

  2. #22
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    Guys, the float switch is McDonnell 150S-HD. This a factory mounted part and UL listed, FM approved, etc. No adjustment is allowed. Download the PDF and you will see on/off is 0.75” @ 150#. I run 80-90# so it will be a little less, maybe 0.625”. So water level is very tightly regulated. That is what is required and it can’t be changed. At least not without permission from authorities having jurisdiction. Given that it has worked perfectly until recent changes, and does so on countless factory packaged boilers, I’m not inclined towards going down that path.

    I do appreciate the input but dual floats, latching relays, increasing hysteresis, and such......just are not viable solutions in this case. Now if anyone has a stash of the old mercury bulb ones I’m all in

    I would be far more comfortable with the TDR if I could see a way to put it across the float switch instead of in series. I don’t want a failure of TDR to impact normal float/pump operation.

  3. #23
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    Quote Originally Posted by Russs57 View Post
    Guys, the float switch is McDonnell 150S-HD. This a factory mounted part and UL listed, FM approved, etc. No adjustment is allowed. Download the PDF and you will see on/off is 0.75” @ 150#. I run 80-90# so it will be a little less, maybe 0.625”. So water level is very tightly regulated. That is what is required and it can’t be changed. At least not without permission from authorities having jurisdiction. Given that it has worked perfectly until recent changes, and does so on countless factory packaged boilers, I’m not inclined towards going down that path.

    I do appreciate the input but dual floats, latching relays, increasing hysteresis, and such......just are not viable solutions in this case. Now if anyone has a stash of the old mercury bulb ones I’m all in

    I would be far more comfortable with the TDR if I could see a way to put it across the float switch instead of in series. I don’t want a failure of TDR to impact normal float/pump operation.
    putting it parallel to your float switch doesn't solve your problem. If float switch closes it overrides the TDR regardles what position it is in. You want a delay after switch closes before the motor contactor can operate again, it has to be in series with the float and motor contactor or it won't do what you want it to do. In series can be before the float, between the float and contactor or after the contactor - any of those locations for the timed contact will work.
    I live for today, I'm just a day behind.

  4. #24
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    Quote Originally Posted by Russs57 View Post
    Guys, the float switch is McDonnell 150S-HD. This a factory mounted part and UL listed, FM approved, etc. No adjustment is allowed. Download the PDF and you will see on/off is 0.75” @ 150#. I run 80-90# so it will be a little less, maybe 0.625”. So water level is very tightly regulated. That is what is required and it can’t be changed. At least not without permission from authorities having jurisdiction. Given that it has worked perfectly until recent changes, and does so on countless factory packaged boilers, I’m not inclined towards going down that path.

    I do appreciate the input but dual floats, latching relays, increasing hysteresis, and such......just are not viable solutions in this case. Now if anyone has a stash of the old mercury bulb ones I’m all in

    I would be far more comfortable with the TDR if I could see a way to put it across the float switch instead of in series. I don’t want a failure of TDR to impact normal float/pump operation.
    As Ingenieur has stated the issue could be best addressed by a duly registered/ certified professional who specializes in boilers. . . and to reiterate Ing the consequence is dire. Boiler upkeep/maintenance are not for wannabes.

    You stated that you are a Maintenance Engineer and I assume you are certified and accredited by NASOE (National Assocation of Stationary Operating Engineers)
    I know cities of Miami and Tampa require it but no state law for persons to have one.

    In CA.,in bigger cities in particular, they undergo rigorous testing and experience to be awarded a license. My next door neighbor Tim is a registered Maint Engineer who is in charge of HVAC of the tallest office building west of the Mississippi. (Union Bank before the new Wilshire Grand L.A) He is due to retire in the next four months having held the job for almost forty years.

    Having said all of above, I would venture to say that whatever were said should not be construed as advice that you should consider in your decision-making process--you are a professional.
    Whatever you decide on is your own judgment call.

    And to reiterate, your scheme of having a parallel FLOAT with TDR contact is untenable to accomplish the thing you are trying to do.
    It violates the Boolean Logic (AND/OR) equation. . . simple Algebra. But is there such a thing as simple Algebra?



    Where:

    Run =1
    Off = 0

    A= TDR
    B=Float switch

    A or B = 1
    A and not B = 1
    B or A = 1
    B and A= 1
    B not A = 1
    A not B = 1

    Not B and not A= 0 (This is the only condition where motor is turned off)

    Maybe, for most, I'm talking nonsense—but this is the only that I can think of explaining it..

  5. #25
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    180415-0941 EDT

    myspark:

    This is not a simple combinatorial logic problem, but involves a timing function, and how that timer function works.

    Suppose the timer is a simple normal "off delay timer". This type of timer asserts its output so long as its input is asserted, and for some period of time after the input assertion is removed. Upon loss of input at any time during the timing function the timer continues to assert its output until time out, but if the input is reasserted during this off delay time, then the off delay timer is reset to 0, and a new off delay is initiated. The time delay relay output assertion is never lost until it times out.

    If A is the float switch contact, and there is no separate isolated contact equal to A or not A, then you can not parallel A (OR it) with a B contact from the time delay relay as this would simply create an electrically latched (held) relay circuit that would remain asserted until power was lost.

    .

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    Quote Originally Posted by gar View Post
    180415-0941 EDT

    myspark:

    This is not a simple combinatorial logic problem, but involves a timing function, and how that timer function works.

    Suppose the timer is a simple normal "off delay timer". This type of timer asserts its output so long as its input is asserted, and for some period of time after the input assertion is removed. Upon loss of input at any time during the timing function the timer continues to assert its output until time out, but if the input is reasserted during this off delay time, then the off delay timer is reset to 0, and a new off delay is initiated. The time delay relay output assertion is never lost until it times out.

    If A is the float switch contact, and there is no separate isolated contact equal to A or not A, then you can not parallel A (OR it) with a B contact from the time delay relay as this would simply create an electrically latched (held) relay circuit that would remain asserted until power was lost.

    .
    OK, points considered—absolutely.
    High five on that analytical insight.

    However, we cannot predict full operation of either float or timer. If we go back to OP's dreaded fear that failure of the timer could disable the system—and he is expecting the float switch to save the day. . . ie. preventing the supply tank from running dry, thereby ruining the pump, then the precise location and almost fail-safe operation of the float switch becomes critical.

    And in the event the timer failed close and the pump keeps running, the float switch will close when the danger level is reached adding a problem to what you already have. . .pump running uncontrollably.

    You can't have the float switch closed 24/7 (or some supplementary timing feature) other wise it will undermine the purpose of the timer. . . complicating the system even more.

    And let's say the timer failed open . . . supply pump will not start until water level reaches the float.

    When this happens, we're back to the oscillating /chattering problem where we started.

  7. #27
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    Quote Originally Posted by gar View Post
    180415-0941 EDT

    myspark:

    This is not a simple combinatorial logic problem, but involves a timing function, and how that timer function works.

    Suppose the timer is a simple normal "off delay timer". This type of timer asserts its output so long as its input is asserted, and for some period of time after the input assertion is removed. Upon loss of input at any time during the timing function the timer continues to assert its output until time out, but if the input is reasserted during this off delay time, then the off delay timer is reset to 0, and a new off delay is initiated. The time delay relay output assertion is never lost until it times out.

    If A is the float switch contact, and there is no separate isolated contact equal to A or not A, then you can not parallel A (OR it) with a B contact from the time delay relay as this would simply create an electrically latched (held) relay circuit that would remain asserted until power was lost.

    .
    As I was following his explanation, only thing wrong with it was it needed to be clarified the timer output contact and the float switch can not be in parallel. Timer power, initiate terminal, etc. need to be driven from something other then float switch. Perhaps an aux contact on the motor contactor to initiate the delay.

    Simplest and least expensive is the ICM203 delay on break unit I mentioned earlier.

    If one is skeptical because they are inexpensive - I have used them many times over the years and seldom had one fail. Buy an extra one if you are really skeptical, very simple to change if they do fail.
    I live for today, I'm just a day behind.

  8. #28
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    first thing measure the time for the deadband
    on to off is 3/4"
    time a few cycles

    a discrete on off system may not be appropriate
    perhaps a loop with pump always on and an approved float valve tapped off it
    the float proportionally opens a needle/seat valve and will hold a tight level
    continuous feed, common strategy

    again, buffers/snubbers in the switch sensing tubes may stabilize the float switch level

    I would not hodge podge a boiler feed water system
    strict asme codes apply
    there is a low level and high pressure safties that shut it down
    finally there is a mechanical blow off/pressure relief, often 2

    I would find the root cause, not patch
    1000's of boilers operate without this issue

  9. #29
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    Quote Originally Posted by Ingenieur View Post
    ...

    I would find the root cause, not patch
    1000's of boilers operate without this issue
    This is really it right here. Study it for understanding.

    It's called the art of steam heating, really science raised to an art level.

    As a young new contractor bidding work, got the wiring bid for two new boilers for a school seven or eight towns away. Prime mechanical contractor was also a new contractor guy I met, friend now.

    Point is we were new and I though the same thing, the other boilers work there must be a way. Design engineer was a very old guy who was getting sued for breaking the boilers on his last job, a high school. Found this out half way through.

    I studied it and figured it out, including addressing the thermal shock.

    Time came to fire it first time and this was very out of character for my friend, never before or since. I had no idea what he was thinking. As soon as it lit he hustled me out of the boiler room to a bar where he bought me a burger and fries, making jokes, what is that flying overhead, that looks like part of those boilers. Look there it is again, looks like a boiler flying overhead.

    Seen a lot of steam and water volcanoes on first fire since then .

    Half way through the maintenance man walks me down to the new wing to show me the new boiler there. He opens the door to this small room and the boiler inside looked like it was coated with 1" snow. I felt sick until he closed the door. Now at this time I can immediately diagnose the cause, but not then.

    My first one, friend prime he had surely done package units but probably his first knockdown. Was toast a year later from no rope between the sections.

    Your TDR is good to go just as soon as you get it listed as a boiler feedwater pump controller.
    Lasciate ogne speranza, voi ch'intrate

  10. #30
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    Different prime, much later. This guy was The master oil heat expert ever since coming off the battleship North Carolina as Sky Captain in WWII.

    It was common to fire with temp burners waiting for the regulars. He says fire it when you're done, they need heat tomorrow morning. Don't worry about set up, they're temp burners. Fired them at 9:30 PM. I watched through the sight glass and the glass immediately carboned over black. I'm thinking 'he's got a smoker'. I left, noticing a little smoke at the top of the stairs. Enormous middle school, had its own huge gym.

    I get a call next morning and he's telling me his call. Principal calls and tells him he was 20 minutes out driving in to school, saw this huge trailing cloud of black smoke, and says to himself 'boy I hope that's not my school'. Turns the corner and says to himself "son of a b... that is my school'.
    Lasciate ogne speranza, voi ch'intrate

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