Steam pressure and potentiometer settings

Grallert

Hello
I would like some direction or confirmation. I've been in charge of running the mechanical systems for this small New England boarding school for one year now. It's a great place. One of the best parts is I get to take care of some pretty neat systems. The main building is heated by a pair of Pacific Steel boilers. Twins but not identical. When I got here I found that the boilers have been running at about 6 or 7 psi. The system is a mix of emitters: steam, steam to water, steam to air and steam to water to air. Some of the radiators are controlled by a very old Johnson control with Johnson Sylphon actuators. This is a two pipe system with about 175 various F&Ts and about 250 traps and four condensate pumps to a condensate receiver than pumped to the boiler that's running at the time. This is more of a steam system than I'm used to. I guess my question is, Am I correct in thinking that 6 or 7 psi is too high? I've lowered the pressure to around 3 but I'm not sure how accurate the gauges are are. I haven't gotten around to adding some better gauges. Also I'm not 100% clear on the potentiometer settings controlling the firing rate.


I've tried to post some pictures, we'll see how that worked out.

Grallert

Grallert

I thought I could get all the pictures in one post, Probably could if I was more familiar with the process.

EBEBRATT-Ed

The modulating control with 3 wires, with terminals R,W & B is the modulating control for the burner (low high fire control. (probably a Honeywell L91B) This control is held out of the circuit and does nothing UNTIL main flame lights and the programing control releases the burner to modulate. This control will try to operate the size of the burner flame in relation to the steam pressure after the main flame lights.

The main setting on this control should be set at a setting below the setting of your operating control that shuts the burner on and off. For instance if you want to maintain 5psi you would set the modulating control L91B main setting at 5 psi The differential setting A<B<C<D & minimum can be set anywhere to match job conditions. The operating control that cycles the burner should be set at about 7psi so it is above the modulating control

If the differential on the L91B set towards minimum you may find the mod motor (low hi fire control motor on burner) hunting or constantly moving back and forth.

If set towards maximum F the motor will adjust and then hold it's position longer.

The differential is basicially adjusting the sensitivity of the control and you should set the differential so the mod motor does not hunt but rather "moves and stops" & moves & stops maybe trying to get it to hold it's position for 5-10 seconds if you can.

Nice job, looks like you have 1 power Flame and 1 Webster burner. Those old pacific's were a decent boiler. Looks like they have been well cared for

Run the lowest pressure you can will save fuel. However beware of having the burner(s) short cycle which kills efficiency. Optimum is to run low pressure with a long burner cycle

Grallert

Thanks for that. We take really good care of these boilers and the system. Gotta keep the kids warn and happy. My goal has been to limit the use of the windows as thermostats and to lower our really big fuel bills. With all the traps and F&Ts I've also tasked myself with cutting the water usage down by keeping the water in the system. I'm getting there. I'm going to print this out and take it to my boiler room.
Yes I have a Power Flame gas/oil and a Cleaver Brookes gas. I like the Power Flame because it's quieter.

Sailah

Ah, snow, NH and steam. Love it.

When we were kids we used to go to the Balsams in Dixville Notch. I loved it. Grand old resort, they had steam heat. I remember it being February and freezing outside, blowing snow and we'd have the windows open because it was so hot with those radiators.

Looks like a beautiful campus.

Grallert

It's a wonderful campus Sailah. We're in the Berkshires. I remember my first of a number of interviews I had here I mentioned that I would bet that 40% of the windows in the mansion would be open in December and January. They said how'd you know that? It's down to about 10%, still too many.
I really love it here.

ChrisJ

I wonder how low you could go and still heat a building like that?
My house is tiny compared to what you're dealing with but some how I'm able to heat all of my radiators evenly with as little was 0.25" WC at the boiler. That's only 0.009 PSI. The only thing limiting my pressure is the size of the boiler.

Can you dial that monster down so it will only run at a pound or two and see what happens? I mean the burners, not the Pressuretrols. Can it run on only one boiler? Is it possible to start off with both boilers and then shut one down once all of the radiators are primed?

Grallert

I'd like to get the burner to run longer at a lower firing rate, as it is now the burner fires, goes up high and slowly drops it's rate until the pressuretrol opens, at about 5psi. I've been lowering the operating pressure to see how the building handles it. I've managed to eliminate most of the crazy hammering everyone here has gotten used to over the past I don't know how many years. I still get a relatively short cycle, this I'd like to extend.
I only run one boiler at a time. I've yet to run them both at the same time, though I've heard it has been done. I can't imagine that we would ever need them both to heat the building.
I really don"t know what the operating pressures for a system like this should be but I do know that it is much happier at a lower pressure, I'm not beating up the traps or the F&Ts and I'm no longer waking the girls in the middle of the night with the monstrous banging. This is a learning process for me.

SWEI

Might want to check the B dimension, and there could be multiple candidates in a big system.

ChrisJ

Grallert said:

I'd like to get the burner to run longer at a lower firing rate, as it is now the burner fires, goes up high and slowly drops it's rate until the pressuretrol opens, at about 5psi. I've been lowering the operating pressure to see how the building handles it. I've managed to eliminate most of the crazy hammering everyone here has gotten used to over the past I don't know how many years. I still get a relatively short cycle, this I'd like to extend.
I only run one boiler at a time. I've yet to run them both at the same time, though I've heard it has been done. I can't imagine that we would ever need them both to heat the building.
I really don"t know what the operating pressures for a system like this should be but I do know that it is much happier at a lower pressure, I'm not beating up the traps or the F&Ts and I'm no longer waking the girls in the middle of the night with the monstrous banging. This is a learning process for me.

Do you have a combustion analyzer and are you trained on working on the burners? Can you downfire them your self or have someone come in and do it?

If it was me, as long as it's safe I'd keep turning the burner down until something stopped heating to find the bottom end of the range.

Grallert

That's the right idea. I do have an analyzer but I'm not trained to adjust the burners. That's on my wish list. I have an outside outfit come and service the them. For years the burners have been run on a manual setting and turned up and down. More often set and forgotten about. Or even worse adjusted by more than one person. So they just bounced on and off the limit. I figured the since we have the controls to run them burners with varying out put should do that. I'll find someone to down fire the burn on the #2 boiler and we'll leave the #1 boiler as is so I can do a comparison.
I'd forgotten how great this sight is, thanks for your input.

bob_46

Ed gave you the straight scoop. You have the controls set opposite of what he said. The letter designations are about 1.5 PSI each and are added to the set point.

EBEBRATT-Ed

Like all the old buildings it should heat?? at 2 psi. Many times to keep the burners from short cycling the pressure is raised and the differential widened to keep the cycling down. Not the best approach but sometimes you have to compromise.

these are full modulation burners, not fixed fire, not two position lo-high fire burners the burner flame can assume any position between lo fire and high fire, that's what is known as "full modulation" using (usually Honeywell series 90 controls)

When @Grallert spoke of adjusting the size of the burner flame he is talking (don't want to put words in his mouth) about adjusting the modulating range, not changing the combustion adjustments of a burner that I assume has been properly set up.

Didn't realize your other burner was a Cleaver-Brooks. LOL, haha now I know who is (most likely) working on your boilers as I am in Western, MA myself.

Grallert

Yes fully modulating. @EBEBATT-Ed. At this point i'm only running the Power Flame. The cycles are to my thinking short. Maybe 5 on, mostly at mid to low fire and 5 off. This was yesterday the 13th with a pressure of about 5psi. The place heats fine in fact over heats in some areas but the could by an issue with the antique Johnson T460 thermostats. If I increase the pressure to prolong the cycle I get the hammering back. To my thinking the short cycling is better that the hammering, as the hammering is was doing some damage. I would love to get these old jennies to run at 3psi but they get there so fast the cycle is even shorter. So Ed could I convince you to visit us here at Miss Hall's for a consultation? Maybe give me a lesson on the operation of my system? I think I'm moving in the right direction, but slowler than I'd like. I'm sure you'd get a kick out of the mechanics and controls of the place. I can't seem to find any one who knows more about these than I do and I only know a little.

Grallert

Here's an update on my questions and the observations I got from you guys. By lowering the diff on the honeywell L91B I've gotten the boiler to cruise along at about 3psi and get plenty of heat to the buildings. Windows are closed and so far no complaints. With the help of Edgemont Precision Rebuilder Inc. who rebuilt some of my obsolete Johnson thermostats it now looks like I have control of the main building.
I'm wondering, it seem that the boiler will run on at 3psi with out stopping. These boiler run on pressure and I know I'm losing pressure in a few places. today we are near design temp. I wonder if it should take a break every now and again? Probably not.

ChrisJ

Grallert said:

Here's an update on my questions and the observations I got from you guys. By lowering the diff on the honeywell L91B I've gotten the boiler to cruise along at about 3psi and get plenty of heat to the buildings. Windows are closed and so far no complaints. With the help of Edgemont Precision Rebuilder Inc. who rebuilt some of my obsolete Johnson thermostats it now looks like I have control of the main building.
I'm wondering, it seem that the boiler will run on at 3psi with out stopping. These boiler run on pressure and I know I'm losing pressure in a few places. today we are near design temp. I wonder if it should take a break every now and again? Probably not.

Breaks are bad.

I wonder if it'd run at 2 PSI with some minor improvements throughout the system.

Sounds like you're making good progress either way!

Grallert

I bet I could. First I'll have to get a proper pair of gauges to cross check with the originals on top.