Carlin Burner Question about Low-High-Low

Jeremy_16

I have a Carlin 702 CRD-W Burner with a low-high-low modulation for the fire. I'm trying to understand how it works. We have one operating pressuretrol for the boiler and a vaporstat that is hooked up to the low-high-low function. The operating pressuretrol is currently set to cut-in at .5 psi and cut-out at 1.5 psi. The vaporstat that controls the low-high-low is set to 14 oz with like a 1 oz differential (the differential is subtractive).



I'm trying to understand how the fire is controlled. Most of the time the low fire is on and other times it switches to high fire for like 30 seconds to a minute. I'm a little confused because I don't understand when it is supposed to switch from one to the other. It's supposed to save on fuel because the burner doesn't need to turn on and off, right? It simply changes pressure by lowering or raising the fire, correct?  I'm not sure where the low-high-low vaporstat should be set. Can anyone explain this to me?



Thanks,

Jeremy

arches

burner operation

Hmm, that sounds backwards. I have a Carlin 801, and I just recently hooked up a vaporstat to regulate the low/high/low control (previously it was only operating at high fire, except for a brief (15 second) startup sequence at low fire).

The way mine works (now) is that it runs on high fire to bring the boiler up to temp and start sending steam through the system. Once pressure (14 oz in my case) is established, the burner falls back to low fire - which consumes about 50% less fuel than high fire. Early in the firing cycle, the burner has trouble maintaining pressure under low fire, so after it falls back 3 oz (to 11 oz) the high fire re-engages. As time progresses (on long cycles) the low fire periods become longer and longer (presumably b/c the systems is fully "saturated" with heat, and all vents are closed). 

The operating pressuretrol doesn't really play much of a role anymore, b/c it is set to cut out at 1.8 lbs, but the system doesn't have a chance to reach those levels.

I contacted Carlin for the operating manual and wiring diagram...I believe its the same (or similar) for the 701 and 801 series. I could try to send you a copy if it helps...although I don't have a scanner (its a paper document). Maybe by fax?

Jeremy_16

arches:

What is the cut-in and cut-out for your operating pressuretrol and what is the cut-in and cut-out for the low-high-low vaporstat?



If the cut-out of your operating pressuretrol is 1.8 lbs does it ever get that high. You seemed to indicate that high fire turns off at 14 oz. and stays off until 11 oz. Does that mean the vaporstat is set to cut-in 11 oz and cut-out 14 oz and that the vaporstat controls the high fire? After the high fire re-engages, what pressure does the system go up to before cutting out or going back low fire?



Does it even matter what the operating pressuretrol is set at? Does pressure ever go higher than the 14 oz the vaporstat is set at?



I have the 702, so it may be different from the 701 to 801 series. How many pages is the operating manual you obtained? Thanks for the help.

arches

low/high/low

The cut in/out for the pressuretrol is 0.5/1.5 lbs (actual cutout was more like 1.8-2.2 lbs according to low pressure gauge). I haven't seen pressure reach the cutout since I installed the new low/high/low control. Previously it used to cycle frequently (btwn high and off) because my boiler is oversized for the system EDR.



The vaporstat cut in/out is 11oz/14oz. When pressure hits 14 oz, the vaporstat  breaks a 110V electrical connection to the high fire oil solenoid valve (shuting down oil flow) and a small air inlet door is partially closed to keep the air/fuel mix in balance on low fire.



The low/high Carlin burners have two oil nozzles. On low fire only the low nozzle is used, on high fire both the low and high nozzles are used. Both are approximately the same size (hence the doubling of fuel consumption on high fire).



I'm still a little perplexed by your system - the way I think about low/high/low is sort of like getting on the highway in your car. From a standstill, you give the engine a lot of fuel (high fire) to get up to highway speeds, and then ease off (low fire) as you catch up with the flow of traffic. From the sounds of it, your system is akin to accelerating at a snails pace and then jamming on the gas when you hit 55 mph. I can see the benefit to the slow acceleration (less chance of generating turbulence/wet steam, etc), but I can't really imagine a scenario where it would be useful to use _more_ fuel once you hit 14 oz pressure. Then again, I'm far from a pro! Anyone else care to comment?

The manual is pretty short...maybe 8 - 10 pages. I can check whether it covers your model when I get home.  

 

arches

no luck on the 702 manual

Looks like my manual only covers 701 and 801 models. Sorry.  You can try giving Carlin a call...800-989-2275. Guy I dealt with is named Mike Martel...nice guy - willing to help, despite my non-professional status.

Here's the text that describes the Low-High-Low firing sequence:

1. Call for Heat. Burner motor and ignition are energized. Air is in the low fire position. The low fire oil valve admits oil to the low fire nozzle and its spray ignites, burning clean with proper air/fuel ratio.

2. If demand exceeds low fire, the damper motor is energized through a high fire operating control (aquastat, airstat, pressuretrol or outdoor thermostat). As the damper motor approaches a wide open position, the auxillary end switch energizes the high fire valve and the full fire with open air burns clean with high efficiency.

3. As the high fire input begins to exceed the demand of the high fire operator, the operating control opens to de-energize the damper motor. As the damper motor returns the air shutter to low fire the auxillary end switch in the damper motor opens and de-energizes the high fire valve.

4. If demand exceeds low fire, the high fire operating control would again call for more heat as in step 2 and then followed by step 3.

5.  If after returning to low fire, the load should drop below the low fire output, the operating limit would shut off the burner completely.

Mike Kusiak_2

Firing rate switching?

Seems like Jeremy's "low"  firing rate is not quite adequate to maintain the 14 oz operating pressure, so when it drops below that level it switches to "high". Having a differential on only 1 oz may contribute to the tendency to switch. Perhaps if you increased the differential to 2 or 3 oz as Arches has done,  you will spend more time in low fire before switching. Another idea might be to decrease the vaporstat setting to say 12 oz, which would possibly be sustainable by the "low" firing rate alone.

Jeremy_16

To clarfiy:

I went back to study the burner again. I hadn't had a chance to post recently. Let me clarify what's going on: When the burner first turns on it goes into high fire to start. It stays there for either a few minutes (if it is a cold start) or less if the pipes are already warm. It then proceeds to go into low fire for a couple of minutes then back to high fire for about 20 to 30 seconds and then back to low fire for a few minutes. It keeps doing this until the thermostat is satisfied. Is this the way it is supposed to operate?

Steamhead

Not really

In your case, low fire is too low. Have a pro rework the firing rates so the low fire is a bit higher, while making sure the high fire remains as is. The air adjustments will also have to be redone, using a digital combustion analyzer.



After this is done, the burner should stay at low fire until the call for heat is satisfied.

Jeremy_16

Steamhead:

I'll mention that to my service tech when he comes back. He definitely ran a few combustion tests last time he was here, but he needed another instrument or gauge that he didn't bring with him so he said he would be back.



So the burner should start up in high fire and then go to low fire until the call for heat is over? Are my vaporstat settings ok?



Thanks.

Steamhead

I think so

what are the high and low firing rates? 

Jeremy_16

Steamhead: High and Low Firing Rates

I finally got the service tech back to try to clear things up. He didn't adjust anything. He told me that there is only one nozzle and the firing rate for the low and high fire is changed by pump pressure. He said that the low fire is 4.25 GPM and the pump runs at 100 pounds pressure and the high fire is around 6.5 GPM and the pump runs 300 pounds of pressure. (hopefully I got all the terms right)



We tried to see how high the boiler pressure went when the boiler was on, but he didn't have a low pressure gauge with him. He said he didn't need one to tell what the pressure was. We were relying on the 30 pound pressure gauge on the boiler. He said we needed to have 1 pound of pressure at the furthest radiator and we didn't even have 1 pound of pressure at the boiler according the the gauge. He adjusted the vaporstat up to 16 oz and it took a very long time to reach that. He said we needed to get more pressure upstairs, but I don't see how that is possible if the vaporstat controlling the fire only goes up to one pound. I'm thinking of bringing a different pro in to take a look. Any advice on what to do from here?

Steamhead

Call someone else next time

you don't need that much steam pressure to begin with, and he should have had a proper gauge. With this setup you really need a low-pressure gauge to get the tuning just right.



I wish you were in Baltimore!

Jeremy_16

Steamhead:

Yeah, it would be A LOT easier if the building were there. I would have called you weeks ago.



I really need to get someone in here with the proper equipment and knowledge. If you or anyone else on here knows of good steam heating specialist in the Boston area, please let me know! I've already started asking a few of my contacts around here if they know of anyone and we'll see what I turn up. Thanks to everyone for the comments and advice.