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

  1. #11
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    Russs57:

    I suspect your original mercury switch was designed with built in mechanical hysteresis. Thus, there was an ON threshold level and an OFF threshold level. The replacement float switch did not have as large a mechanical hysteresis as the original.

    Ideally as others have mentioned you want a level control that has hysteresis based on level rather than time.

    If you can not find a mechanical level switch with this built in liquid level hysteresis, then you want a two probe system of some sort. Many exist.

    A highly reliable system can be built with two electrical probes. one for high and the other for low. For a pump-up system the lower probe sets an electrically held relay, and the upper probe drops out the electrically held relay.

    If this is designed with a NO contact controling the motor, then the system is fail safe to not overflow on loss of power to the relay.

    In the early 60s I did some development work for the Charles F. Warrick Co. on electronic liquid level controls. At that time they made quite reliable relay type systems using using conductive probes, a high voltage source, and sensitive AC relays. Around the end of the 60s Warrick was sold, and then again to a company called GEMS. See https://www.gemssensors.com/level/warrick

    .

  2. #12
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    All that above, plus...

    As kwired said, if the pump is running only 11-12 seconds every minute then either it's too big or the on/off points are too close (are they trying to regulate the water lever to within an inch?). How big is this boiler, anyway?

    Those relays are also called Delay-On-Release.

  3. #13
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    Quote Originally Posted by Russs57 View Post
    Gentlemen, I need your advice on an electrical solution to solve a problem I am having. While the problem is more mechanical in nature I can’t address it that way.

    I have a float switch that is mounted on a boiler. This float switch sends 120 VAC to the coil of a motor starter. As the water level starts to rise in the boiler the float starts bouncing, causing the motor starter to chatter badly. At times the contacts in the motor starter are welding themselves together. There are things that have changed on the boiler(s); new (excessive) loads, old floats switches were mercury bulbs and new ones are snap switches, water chemistry (well let’s not go there). While it isn’t the right way I need to consider an electrical solution, provided it is safe/legal.

    ...
    If it's mechanically deficient, you cannot fix that with a non standard electrical solution, a variance from the normal standard way of doing things. Not with a boiler.

    With steam you can get surging, water sloshing back and forth in the boiler. I believe this is caused by a scum layer on top of the water and there is a skimming procedure for cleaning this out. It's a boiler manufacturer stated procedure.

    If you think the pump is pumping too fast, you can throttle the flow down by restricting with the valve in the line.

    Seen both. If that does not work and you think you need a timer, I would think you need a new float switch assembly, recommended for that boiler by the float manufacturer. The one you have may be misapplied.

    Before you go forward with a timer, call the existing float manufacturer and see what they say. There is no way they are going to approve the timer but they may be able to point you to the correct solution.
    Lasciate ogne speranza, voi ch'intrate

  4. #14
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    Sorry I have not been able to respond before now.

    Boilers are a pair of 250 horsepower, 1998 Cleaver Brooks fire tube boilers. They have worked perfectly until new management took over, hired new water treatment company, decided I’m not allowed to check water chemistry, and added a huge heat exchanger load in excess of 250 boiler horsepower. IMHO problem is 80% water chemistry and 20% load related. I’m not at liberty to change either. Had a decent chemical rep but brain tumor forced retirement and last two guys aren’t so swift. It is what it is.

    Boiler controls are a little unique. In general you can’t repair or adjust them, other than set cut-in/cut-out points on pressure switches. Rest assured I’m using the correct float switch and a new one makes no difference. Suffice to say even when water chemistry is perfect I still have a slight problem with motor starters chattering. Nothing that causes anything more than premature wear on said motor stater.

    Problem is right now I have a dead chemical feed pump. I’m in a situation where a brand new pump and motor starter is chattering so much, contacts weld together, then one fuse blows, and pump single phases. Once it managed to hang in there long enough to fill the entire steam piping up to second floor level! Comes a point where I can’t look the other way no matter what kinda idiots I’m employed by. Rest assured after 33 years of top level evaluations I’m now a huge trouble maker who can’t get with the program. Sad thing is this is a hospital.

    So yes, I understand what approach should be taken but right now I need to buy some time and prevent the new pump from getting destroyed from single phasing. Sorry I didn’t learn how to post a schematic but thought the description of float activating TDR trigger was adequate. I can see now that TDR must be in series, otherwise trigger would never drop in/out to restablish time delay.

    Last but not least allow me to express my gratitude for so many freely sharing such a vast knowledge base. Sometimes the internet gives me hope for humanity!

  5. #15
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    First thing to clarify is if you have short cycling due to the float and water level or chattering of the contactor, which would probably be caused by the contactor itself or low control circuit voltage / bad control circuit connection.

    Short cycling on water level I cannot see happening faster than 1 - 2 seconds / cycle, even with the pump directed right onto the float, while chattering due to bad control circuit voltage could make the contactor work like a buzzer. Which problem do you have?

    Replacing the starter sounds like it should already be on the list. You cannot wear out or beat up a NEMA rated starter with short cycling on a good float switch. Chattering may be an electrical problem.

    The steam boiler will be sensitive to water level, or I should say, the boiler's manufacturer. You will want to follow Cleaver Brooks instructions and advice regarding the float and it working properly, exactly. Giving Cleaver Brooks a call and running this by them should also be on the list.

    Float switch would be specific to the boiler but pressure you should be able to choose, for the operating control. The burner is either high low fire or fully modulating, and trying to control that with independent pressuretrols can be a task to set up properly. An electronic control, A Heat Timer product for the pressure operating control that matches the burner type, high low or fully modulating, would be on my list. Lot easier to install a Heat Timer and be done with it than to try coordinating independent pressuretrols for high low fire.

    Troublemaking is relative. I can make this point to them very easily and only once, then you will be golden.
    Lasciate ogne speranza, voi ch'intrate

  6. #16
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    Moab, UT USA
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    Steam Boiler Operation

    I advise you to walk away from this one if you can or otherwise ask for a very solid Boiler Outfit to shadow you on the matter.
    I have 30 years diversified experience and I ran Boilers for Texas A&M. I have 2 small 15 PSI rigs in my charge currently.
    You have a Boiler System Problem that needs to be addressed by a Qualified Boiler Outfit, because based on what you are telling me, the system is borderline and dangerous.
    The makeup water control you are refrerring to is called the McDonnel Switch by old school guys. Many Boilers are set up in shade tree manners that half way work and can become very dangerous if they are not understood and dealt with from a standpoint of high expertise in knowing what can go wrong. Its very much like electricity and more about knowing what not to do.
    The water in the " water column " should not be rocking like you describe. This points to a deeper problem and the makeup water ciircuit should never be modified away from tried and true convention. Same thing with the firing controls. Feedwater pump operation whether duplex or single should be cyclic, and smooth. Anything that could cause short cycling raises and immediate black flag.
    It sounds like you have multiple issues that are impacting.
    While water chemistry is important, getting it right is not going to bring back a boiler that is massively scaled up without a comprehensive approach.
    Your Conductivity, TDS, PH, and Chemical levels have to be in step with your cycles of concentration.
    The McDonnel switch aside from running the makeup water pumps as a general rule provides primary " Low Water Failure " protection, but this is only one part of the safety equation regarding a low water event.
    The increased load sounds bothersome as well.
    This is a problem for a Boiler Service Outfit in real terms.
    I would insist on help so you both have some support in the form of outside expertise and more minds working on what I consider a serious matter.
    Last edited by StarCat; 04-12-18 at 04:06 PM.
    Microwave Radiation Dangers should be openly discussed

  7. #17
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    Gentlemen, rest assured current problems are not the norm. Nothing has been cobbled together. Operating controls are correct. There is no scale in the boiler, etc. It is definitely the float that is making and breaking. The time periods of pump operation given were just for illustration of what I needed from time delay relay. Yes my feed water pump may be oversized according to some but I wish it to deliver 150% of steaming rate at maximum working pressure.

    I just have a temporary situation I need to address. Perhaps the best thing to do is remove said boiler from service until new chemical pump arrives. I was thinking adding the TDR would be a quick and easy fix to a temporary problem. But it never hurts to ask for a peer review. Sounds like most think I shouldn’t, so I won’t.

  8. #18
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    Quote Originally Posted by Ingenieur View Post
    I would use a latching arrangement
    as float hits the on level it energizes a relay that latches itself in
    this relay also starts the pump, it runs until the float switch hits the off level and interrupts/breaks the latch
    The schema presented doesn't seem to represent the intended task. The inclusion of a latching relay would probably serve a purpose but the signals to latch and unlatch are missing. Were this ellipted on purpose?

    For this control system to eliminate the chattering (which is OP's primary concern) I would think that you will need two signals from two level sensors--one to latch and another one to unlatch.

    But then, when you do that, you wouldn't need a latching relay.

    Am I missing something or am I still having this jet lag after a 12-hour flight from Munich?

  9. #19
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    I have used time delay relays on multiple jobs where float switches and small tanks/over-sized pumps were an issue. I personally like the FUJI multi-function relays. If you ever pull it out you can use it for other things. Time range from .05 sec to 60 hours. 100 to 240 VAC coil, DPDT. Capable of ON Delay, Off Delay, FLicker, ONE Shot (allows an item to turn on only once for a certain time, and then needs a signal to restart). Plus they are cheap.

    Time Delay Relay (multi modes)
    https://www.automationdirect.com/adc...)/MS4SM-AP-ADC

    Socket
    https://www.automationdirect.com/adc...Series)/TP411X

  10. #20
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    Quote Originally Posted by myspark View Post
    The schema presented doesn't seem to represent the intended task. The inclusion of a latching relay would probably serve a purpose but the signals to latch and unlatch are missing. Were this ellipted on purpose?

    For this control system to eliminate the chattering (which is OP's primary concern) I would think that you will need two signals from two level sensors--one to latch and another one to unlatch.

    But then, when you do that, you wouldn't need a latching relay.

    Am I missing something or am I still having this jet lag after a 12-hour flight from Munich?

    it's on there, the dashed lines are the float(s) ie field devices, iirc dashed lines are the std way to depict field or non-pnl located devices
    simple 3 wire latching control scheme
    fill is 'start'
    full is 'stop'
    yes, you need a form c level switch

    one contact is an issue
    say the float hangs down, contact makes, pump runs
    as soon as the level rises a bit the float is not vertical and contact opens
    short cycles, no contollable deadband, and at the transition, partially hanging/floating, the contacts will open/close until it rises enough to establish a stable position

    there are very specific controls made for this application
    iirc it is like elevator work and the devices must be certified for use on boilers
    https://estore.industrialcontrolsonl...es/MM-825r.pdf
    Last edited by Ingenieur; 04-13-18 at 07:05 PM.

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