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

[Russs57]

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.

I’m proposing to install a time delay relay across float switch contacts. This way the float switch would still operate feed water pump motor starter if time delay relay failed. It looks like an off delay, with power trigger (S break), is what I need. I would want the time delay quite short, just long enough to cover any bounce in the float switch.

Just to be clear, assume float switch calls for the pump to start every sixty seconds. Pump runs an average of 11 seconds. During the last two to three seconds of pump operation, motor starter drops in an out repeatedly. I’ll install the time delay relay in parallel with float switch. Input voltage will be a continuous 120 VAC. The float switch will provide a 120 VAC power trigger to the time delay relay. Time delay will be set rather short, say 0.25 seconds. Upon closure of float switch, trigger is energized and relay contacts close. Once float switch opens and trigger is removed, and relay contacts start timing open…..unless trigger is closed again before timing out, in which case time delay is reset and relay contacts stay closed until trigger is removed for time exceeding the time delay setting.

So, what do you guys think? Is it safe/legal? Am I picking the right time delay relay type? If said relay is a “universal” voltage (24-240 VAC) will the bouncing float switch let voltage drop enough to reset time delay or should I look for something that only uses a 120 VAC trigger? Any better (electrical) ideas on how to solve my problem?

BTW, pump is 3 phase, 480 VAC, size one NEMA motor starters with electronic overload relay.

 

[Barbqranch]

I had a similar problem with a storage tank on a RO system. I used an on-delay relay, set for 1 second or so, which was on the output of the float switch. It closed an ice cube relay that then operated the pump motor. This way, the switch had to quit oscillating before the pump would come on.

 

[petersonra]

You might be able to make this work with an off delay timer. You will want to wire the switch to the timer and use the timer contacts to control the pump.

Best bet is a switch to turn it on and another one to turn it off. Often you can get such an arrangement in one package.

You might also be able to set the deadband on your switch. A few come with such an adjustment but usually not the lower cost units.

 

[Jraef]

Although it could be, this is not typically done with a timer, it's done with the hysteresis (difference between On and Off) of the float switch. Old mechanical float switches would have an adjustment for this. But what happens sometimes is that an old rod or chain operated float goes bad and a replacement can't be found, so it is replaced with a mercury or some other type of simpler "tilting" type of float switch, and that's where this sort of issue happens. When using a tilting float switch system, you should use TWO of them, one set as the On, one set as the Off level.

But assuming that's not an option for you now, yes it can be done with a timer. You would use what's called an "Off Delay" timer, also known as "Delay On De-Energization", abbreviated as DOD (as opposed to DOE). On that type of timer, energizing the coil changes the state of the contacts immediately, just like any relay. So in your application you would use the Normally Open Timed-to-Open (N.O.T.O.) contacts and feed the circuit through those to yopur starter coil. But unlike a relay, when the coil is dropped out the timer KEEPS the contacts from opening again, until AFTER the time expires. In that scenario if the coil is re-energized before time expires, it simply resets the time and the contacts stay closed. So it acts as a "minimum run timer" for the pump.

The tricky part in using a timer is that you MUST ensure than at no point can the time value exceed the amount of time it takes the pump to go dry. That's where the second tilting float switch is better.

 

[gar]

180410-1457 EDT

Russs57:

You want what what I would describe as an off delay relay. You need to study how a particular relay works with a particular name label.

What I mean by an off delay here is that ---

1. The relay output contact closes immediately on application of the input control signal to the timing relay.

2. The relay output contact remains closed so long as the input control signal is present, and the output contact remains closed for a predetermined time after the input control signal is removed.

3. If the input control signal is reapplied during the timing out time, then the timing circuit is reset so that full time out time exists for next loss of the input control signal.

.

 

[ActionDave]

I'm not understanding the bouncing float. I understand how it could happen but float switches are designed to prevent this.

 

[Ingenieur]

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

 

[Jraef]

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

Right. But we can assume, since it IS bouncing, that he does not have a hysteresis in the float switch. So he either needs a different floatie, a second one like the one he has, or the off delay timer. Were it me, I would use the second floatie.

 

[Ingenieur]

Right. But we can assume, since it IS bouncing, that he does not have a hysteresis in the float switch. So he either needs a different floatie, a second one like the one he has, or the off delay timer. Were it me, I would use the second floatie.

most I've worked with are 3 w, form c
otherwise upon fall/low it would make starting the pump
as soon as it was elevated a small amount it would turn off
fall again, repeat, short cycle, it may though, 60 sec off, 11 sec on
50 starts an hour
but who knows
this sounds like a control strategy issue requiring more than a patch
sounds like boiler feed water, definitely not a system to cobble together lol

one sketch
one data sheet
and one sentence would give us far more info than the long op

 

[kwired]

How large is this boiler. One I am familiar with holds enough water that when feed pump runs it maybe runs for about 30 seconds, but typically won't run again for at least 15 - 20 minutes. To start every 60 seconds and only run for about 11 seconds sounds like maybe too large of a pump for the application and is possibly adding to the issue. May be hard on pump motor to have that many starts per hour also.

That said a fairly inexpensive delay timer is ICM 203. You may be able to find one for under $10, works on 18-240 volts, adjustable from 1.8 seconds to 10 minutes. Only a two terminal encapsulated device with time adjust knob. Place in series with your motor controller coil. Any time the power has been removed it won't let it run again until the time delay is up.

Sold at HVAC supply houses as an anti short cycle timer for HVAC equipment if you can't find it elsewhere.

 

[gar]

180410-2221 EDT

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

.

 

[zbang]

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.

 

[__dan]

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.

 

[Russs57]

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!

 

[__dan]

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.

 

[StarCat]

Steam Boiler Operation

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.

 

[Russs57]

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.

 

[RumRunner]

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?

 

[SSDriver]

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/ad...er_Relays_1-z-16_DIN_(MS_Series)/MS4SM-AP-ADC

Socket
https://www.automationdirect.com/ad...ic_Timer_Relays_1-z-16_DIN_(MS_Series)/TP411X

 

[Ingenieur]

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.industrialcontrolsonline.com/Customer/incodi/specpages/MM-825r.pdf