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

[Ingenieur]

the switches are mntd external to the boiler
example https://media.statesupply.com/filem...4-combo-lwco-pump_controller_instructions.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

 

[Russs57]

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.

 

[kwired]

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.

 

[RumRunner]

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..

 

[gar]

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.

.

 

[RumRunner]

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.

 

[kwired]

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.

 

[Ingenieur]

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

 

[__dan]

...

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.

 

[__dan]

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'.

 

[JFletcher]

I personally would not modify the boiler in any way, shape, or form. While it may be electrically possible to achieve what you desire, it's certainly is not recommended, and you know that it isn't the proper way. Some random or fluke failure in your modifications could have unintended consequences that lead to disastrous results.

The next time the hospital wants you to do something that is questionable, what then? If an elevator messes up, are you going to fix it, or are you going to tell them to call Thyssen-Krupp (or w/e mfg you have) and have it fixed properly?

 

[kwired]

I personally would not modify the boiler in any way, shape, or form. While it may be electrically possible to achieve what you desire, it's certainly is not recommended, and you know that it isn't the proper way. Some random or fluke failure in your modifications could have unintended consequences that lead to disastrous results.

The next time the hospital wants you to do something that is questionable, what then? If an elevator messes up, are you going to fix it, or are you going to tell them to call Thyssen-Krupp (or w/e mfg you have) and have it fixed properly?

Other factors come into play. Probably nothing wrong with replacing worn out or malfunctioning components with same thing. Problem he did present however sounds like something has probably changed and maybe does need a boiler expert to look into it. Still sounds like too narrow of a hysteresis band on the control for some reason is the biggest problem here. Presuming it wasn't always that narrow and something has changed, whether intentional change or not.

 

[gar]

180417-1223 EDT

Russs57:

Following is a method that should make you no worse off than you presently are. However, you must determine the root cause of your problem. I suspect that the replacement float switch does not have the level or time hysteresis that the mercury contact float switch had.

Presently you have contactor failures where the contacts weld together. This will cause overfilling. Failure in one mode of the following method will be no worse than welded contacts, and in the other mode no worse than the float switch alone.

This method uses a timer that is edge triggered on closure of the float switch, and has a contact closure in parallel with the float switch contacts.

This timer is powered from the float switch output, basically the same signal as is applied to the contactor coil. Upon powering the timer its output contacts close. These contacts are in parallel with the float switch contacts. This maintains power to both the timer and the contactor coil for the duration of the timer period independent of whether or not the float contacts open.

At the end of the timer period the timer contacts open, and only the float switch determines whether the motor and timer are powered.

When the float switch opens the timer and motor are depowered. This resets the timer, and turns the motor off.

Basically this debounces the float switch contacts.

.

 

[Russs57]

Thyssen-Krupp.....oh I hope you are having better luck with them than I am! We call them thieves and crooks.

Gentlemen, as mentioned in the beginning, the root problem is water chemistry caused by a bad chemical feed pump. That pump was finally replaced yesterday. A large load that has been added a couple of years ago also hurts matters but that is easily managed. Bad water chemistry creates excessive surface tension on the water and foaming in the boiler.

 

[JFletcher]

Thyssen-Krupp.....oh I hope you are having better luck with them than I am! We call them thieves and crooks.

Gentlemen, as mentioned in the beginning, the root problem is water chemistry caused by a bad chemical feed pump. That pump was finally replaced yesterday. A large load that has been added a couple of years ago also hurts matters but that is easily managed. Bad water chemistry creates excessive surface tension on the water and foaming in the boiler.

hopefully the new chemical feed pump will solve the problems you are attempting to fix electrically. As for the elevator, last time I worked for a place that needed elevator repair on that brand, there are only two license shops in the state that would work on them. I believe they sent two techs for an entire day, due mostly to driving distance... and that is not inexpensive. replacing a $10 relay could cost $2,000.

 

[Ingenieur]

funny boiler story
in the 80's in an AK village named Bethel I was assigned some work to expand a HS

It had 2 large steam boilers, firebox type
I hired a company to clean and inspect to get an idea of servicability
a tech opened the access portal and climbed in

next thing I hear him laughing his butt off
he tells me to get in and look
in the corner was an ~6" clay model of snl's mr bill, it was fired rock hard
must have been left by a previous tech
we left it

probably still there