Interrupted vs intermittent Primary control
Is there any reason when replacing a primary control not to always use a Interrupted duty ignition primary, even on older systems that have an intermittent duty primary?
Thanks in advance!
Comments
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Better to drop out the ignition …
There was an error rendering this rich post.
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I don't see any reason to use an intermittent ignition control. It's like holding a lighter up to a candle that's already burning. Intermittent ignition controls just put unnecessary wear and tear on the ignition transformer/electronic igniter and electrodes.
I recommend replacing every intermittent ignition control that I come across. The new digital interrupted ignition primary controls improve reliability and provide better safety when setup for a 10 or 15 second trial for ignition instead of the 45 second trial for ignition the old intermittent ignition controls have.
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Some of the flame retention pattern burners actually burn better when the ignition is not trying to light the oil so close to the nozzle spray. If you look at the sequence of ignition of a flame retention burner you can see that:
- The spark starts before the fan and pump gets up to full speed
- Once the fan gets to about 80% of the speed, the fuel pump pressure valve opens and fuel spray is ignited
- As soon as the pump gets to full speed the oil spray will start to fill the combustion chamber
- Then the low pressure area of the flame head draws some oil back to the slotted head to get a second chance at burning without adding a lot of excess air, then the flame pattern fills the fire box.
At this point the flame is so hot that it will sustain itself as long as there is the proper air and fuel mixture. The ignition spark only interferes with the oil spray close to the nozzle making un even combustion near the start of the spray pattern. In many cases the flame actually gets quieter once the ignition drops out.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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Many old stack relays had interrupted ignition, but that started to disappear in the late 1960s. Only thing I can figure is they didn't want to spend the extra money on a separate internal relay for the ignition. fuel was cheap back then.
I agree with @Big Ed_4 , @SuperTech and @EdTheHeaterMan . Unless it's a really weird setup, those old 3-wire, intermittent-ignition primaries get replaced, and delay valves get added. Here's how we deal with a combo aquastat relay/oil primary control:
All Steamed Up, Inc.
Towson, MD, USA
Steam, Vapor & Hot-Water Heating Specialists
Oil & Gas Burner Service
Consulting0 -
That is all fine nowadays. But some of the old crappy burners we had in the old days wouldn't stay lit reliably without the ignition on. Most job back then were constant (intermittent) ignition. I remember some burner ran better with the ignition on and some were better with it off.
But this was in the days of non flame retention burners.
I liked it better when it was called constant or intermittent than
intermittent and interrupted like they do now.
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@EBEBRATT-Ed + constant Ignition = showing our age = LOL
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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Why would anyone refer to constant ignition as "intermittent"? That is completely wrong.
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Somehow that changed years ago. When I started constant ignition was defined as "the ignition transformer stays on during the entire burner run time" Intermittent was "The ignition is on when the burner starts and is off at a predetermined time"
Somehow this was changed to intermittent (instead of constant) and interrupted (instead of intermittent)
It just adds to the confusion.
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It certainly does.
I could never use the word "intermittent" for a control that held the transformer on for the entire cycle. That's flat out wrong. Everyone should abandon it.
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ISTR this was done to bring the oil terminology in line with that used for gas. So, "constant" would be a pilot light that stays on all the time, "intermittent" would be a pilot (gas) or ignitor (gas or oil) that comes on at the start of a firing cycle and shuts off at the end, as on a spark-to-pilot or hot-surface gas ignition system or an oil system where the spark stays on the whole time the burner runs, and "interrupted" is where the ignition only stays on when lighting the fire.
All Steamed Up, Inc.
Towson, MD, USA
Steam, Vapor & Hot-Water Heating Specialists
Oil & Gas Burner Service
Consulting2 -
Your the man Ed! I have read about this in several documents and have a much better understanding after absorbing your reply!
Robert
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It doesn't power the transformer while the burner is idle, so it's intermittent. I agree it's stupid. The motor is also intermittent. I'm intermittent.
I remember some customers complaining about TV reception after converting from a stack relay to cad cell primary with intermittent ignition. As mentioned, the stack primary had interrupted ignition. I can't remember if it was VHF or early cable, but they weren't happy.
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So there are some of the smaller gas power burners like a PowerFlame where they light the pilot with a spark, prove the pilot and then light the main flame then shut off the spark and keep the pilot solenoid open along with the main burner.
Wonder what to call that? The terminology make no sense.
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Double Interrupted ingnition! :D
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@EBEBRATT-Ed & @EdTheHeaterMan grew up during a time when Oil Heat guys didn't touch Gas Heat and Gas Heat service was Installed by plumbers and repaired by Gas utility Company employees. So there was never any confusion regarding Constant ignition and Intermittent Ignition. When the Gas utility Companies started to do less and less repair service, then the plumbers needed to learn how to do the repairs. then the oil heat guys also needed to fix a gas heater from time to time. Eventually there were not longer a difference between working on oil or gas. you just worked on HEATERS.
Then someone needed to start calling pilots Constant ignition. Spark during the entire run cycle Intermittent formerly constant, YEP! that is what it said on the box. Intermittent formerly constant ignition. Then the other controls were labeled Interrupted formerly Intermittent controls. That ticked off the old timers and some of them just stopped working on that stuff altogether. I's surprised that @EBEBRATT-Ed still is doing that stuff. You are showing your age again ED
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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Occasionally I found it necessary to switch to "constant" ignition to keep the flame stabilized temporarily under adverse conditions such as: some water in the fuel, extremely cold fuel, an antiquated or damaged burner, just to get the heat on until proper repairs could be made.
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