Schematic/Suggesstions Needed

JJW101

Hello Folks.

While I have got over 25 years experience in the Residential world, Commercial is a bit new to me ( I have worked on some over the years, but am by no means an expert). I recently stepped out of the world of self employment, taking a pretty solid job as a facilities manager with my local county government, specifically in charge of the mechanical systems, fire protection, and boilers.

Our heating plant has 2 fire tube boilers, 1 Cleaver Brooks, 1 Kewanee. It seems that there have been plenty of boiler operators over the years, and a few outside vendors as well. Each has made some changes here and there, and I am faced with needing to troubleshoot our make-up tank and fill system, which is a bit of a special case.

We have one makeup tank, with 3 pumps - 1 for each boiler, and 1 to act as a backup. I have no diagrams/schematics of any kind, and I am wondering if anyone may have a source for a diagram/schematic with a single pump, single boiler system that I can use as a starting point in solving this rats nest.( I have 2 McDonnell Miller lwco's on each boiler, 3 pressure-trols on each boiler, a float switch at each pump, and a McDonnell Miller 150 float activating the solenoid on the water inlet. I doubt anyone will have a schematic that fits this exact need, so I am hoping to get a simplified one that I can build off of during the troubleshooting process.

My main issue is that the makeup tank is overfilling. I have pretty much ruled out this actually being an electro-mechanical issue, in that it continues to happen after I have closed the calves on the water supply, so It is probably an issue with condensate being very slow to make its way back to the tank, but I feel this would be an ideal time to get a handle on the wiring since I am already dealing with this problem.

Thanks in advance for any help any of you can put on the table.

Jamie Hall

Aren't you going to have fun. To start with, there are two fundamentally different ways of handling makeup tanks -- one is to have what I refer to as boiler feed pumps, and the other is to have what I refer to as condensate return pumps. The former (which to my mind is preferable!) has the pump from the condensate tank activated by one of the low water cutoffs on the boiler (many McDonnell Milers have two contacts at slightly different elevations -- the upper being NO and closing on drop, the lower NC and opening on drop, with the upper activating a water feeder or in this case the boiler feed pump and the lower shutting off the burner(s)). The other type has the pump activated by a float in the condensate tank itself, with no reference to the boiler water level.

So -- the first step is to find out what activates each of those pumps. You may be able to do it just by wire tracing, but if things have been modified and the modifications modified you may just have to try the various controls to see which one turns on what. Once you do, label both ends of all the wires -- clearly! -- as to what they do!. Also, this would be a very good time to start making a line diagram of all the controls and the tank and pumps and boilers.

ratio

Also, keep in mind that sometimes the only thing to do is tear it all out (I'm speaking about the wiring here, not the piping!!!) and start over. In particular, with a simple system that's been "fixed" a goodly number of times by "techs" of "questionable talent" or " limited knowledge" (see what I did there?), it's often faster to figure out what it's supposed to do & make it do that, rather than figure out what it is currently doing & then make it work from there.

Jamie Hall

ratio said:

Also, keep in mind that sometimes the only thing to do is tear it all out (I'm speaking about the wiring here, not the piping!!!) and start over. In particular, with a simple system that's been "fixed" a goodly number of times by "techs" of "questionable talent" or " limited knowledge" (see what I did there?), it's often faster to figure out what it's supposed to do & make it do that, rather than figure out what it is currently doing & then make it work from there.

And in doing that you may -- without even being aware of it -- fix something which was silly, idiotic, or downright dangerous (the if you look at it you say "they can't possibly have done that" but they did moment.)

EBEBRATT-Ed

right up my alley. Each boiler has a pump control. Probably a McDonnell Miller #150. They may be using this as a pump control only or as a combination pump control & low water cutoff. Take the cover off and you will find two switches inside. One is NC (with a normal water level) that's the LWCO switch and the other is NO that runs the pump.

BE CAREFUL there is usually two sources of power inside the control one from the burner circuit for the lwco and one from the feed tank for the pump control.

the float switches on the feed tank are probably wired in to act as low water cut offs for the pumps (don't want to run them dry)

there would be a float control on the feed tank to control the make up solenoid valve.

The three pressure controls on the boiler would be. RED, white and blue 3 wire (probably a Honeywell L91A or B which is a 3 wire series 90 135 ohm modulating control. This controls the burner lo-high fire.

Probably 1 pressure control is a Honeywell L404E manual reset high limit (it will have a metal reset lever on top of it)

the other pressure control is probably a Honeywell L404A which is your steam operating control.

You didn't mention motorized valve in the feed water piping do you have those??

If you can find the nameplate on the feed tank you may be able to find a diagram from the MFG.

Could be a Skidmore, Hoffman, Shipco, Clever Brooks, Kewanee etc.

best I can do with what I got

JUGHNE

I have worked on a set of fire tube NG Kewanee (alternating weekly) in a hospital.
Each has water feed/LWCO combo that runs its own ped pump in a single cond return pit. The pit has make up water control as Ed described above.
One boiler has a newer MM157S and the other is the original feed/LWCO from 1970's with Hg switches inside.

Each also has, set at a slightly lower water level, a combo LWCO/fill valve, float operated. If feeder pump fails fill valve will add CW into boiler return. Either LWCO will stop the burner of course, but I believe only the LWCO/fill will show the low water light on the burner control panel.

As Ed said each feeder pump has it's own power supply circuit.
The LWCO circuit comes from the burner control. 2 circuits in one JB!

I had to change out the Flame Safeguard HW controls from the R4140 to the newer RM7840 design. The sub base and control wiring had to be modified. The original control wiring was all red wires, nicely numbered with wrap tabs. However the numbers were all lying in the bottom of the control box.
Because of that ID not readily available, no wiring diagram and the fact of some cobbling jacking over the years, I traced out every wire. Changing some as needed. If you come across some cobble work I would recommend getting as many different wire colors as possible and replace. I used #14 stranded with crimp connectors. Loop continuous control wiring as much as possible and avoid wire nuts in JB if possible. Much easier to troubleshoot and eliminate mistakes with more colors.

The Kewanee control has over 30 control wires entering and they were all red. These have the same 3 pressure controls as yours plus an additional variety of safety switches.

One other thing for the feed pumps. In this situation the pumps have a pretty high flow. They would short cycle a lot and wire draw the inline check valves seats. I recommended that they throttle the discharge some to avoid that wear.

Also, if it were a problem, it would also delay the CW feed to the return pit from adding fresh water allowing the cond return to possibly catch up. But must be a balance to avoid LWCO shut down of boiler.