Pump speed control - How do you guys do it?

CMadatMe

Apple and a Orange.

Lamda is quite different from air fuel ratio and is what the boiler uses. Yes on initial start the air flow is set to the start rate by controlling the fan speed. Once this is done the gas valve opens and the gas flow rate is electronically regulated, increasing slowly until the burner ignites. During the calibration period the fuel flow is checked against the optimum flame signal and the correct lamda setting is determined for the current burner cycle. The Lamda calibration is the maximum flame signal representig a Lamda value of 1 which is 0% excess air The burner is taken beyond the Lamda 1.0 point and then back to calibrate the burner for that cycle. The burner matains a Lamda point of 1.3 for each cycle. No matter whether burning rich or lean fan speed does not change gas flow changes.



Air does its own thing and gas does its own thing. They work independent. The gas valve operates off the Ionisation current feed by the Ionisation electrode.. If i'm burning rich gas valve backs off not fan speed until I get back to Lamda of 1,3. If I'm burning lean gas valve opens until I get back to Lamda 1,3. fan speed does not increase nor decrease.



This allows for optimum burn on every fire and really shows up on LP jobs and as natural gas suppliers begin adding fillers to the gas line during peak times.



I don't claim to be a physists heck I can't even spell it.

croydoncorgi

We'll have to totally disagree on this

Quote: Air does its own thing and gas does its own thing. They work independent. The gas valve operates off the Ionisation current feed by the Ionisation electrode.. If i'm burning rich gas valve backs off not fan speed until I get back to Lamda of 1,3. If I'm burning lean gas valve opens until I get back to Lamda 1,3. fan speed does not increase nor decrease.Unless you work for Viessmann AND have been on training courses (in Germany?) that gave you this information directly, I'm prepared to state that your description of what happens is wrong.For a start,  my Viessmann documentation says that the ionization-current-based adjustment of the gas valve can only happen with the boiler at full power, and it actually throttles-up for 5 seconds or so, periodically, to check the adjustment.  As I said, the whole principle of the gas train is that the venturi / zero-pressure valve combination gives a more-or-less constant gas/air ratio across the full power range.  So all that needs to happen to make the thing throttle-up is to increase the fan RPM.  Adjustments to the gas-valve using the ionisation current input happen only every few hours, I believe.  But the controller automatically adjusts the power output continuously, every few seconds, and only via changes to the fan RPM.

CMadatMe

I Can't

Site won't let me post a Macromedia Flash video animation I have the pleasure to get from Viessmann which shows exactly what I am trying to explain. Yes air changes as it ramps up and down but that does not tell the gas valve to open or close the ionisation current does..Burning rich get your foot off the gas, burning lean give me some gas. My understanding is this is a constant. Yes at times it looks to calibrate but it is always monitoring and sending ionisation current feedback to the control.

bob_46

Correction

I stand corrected. I thought Viessmann figured out how to do O2 trim on the cheap by using flame signal instead of an O2 sensor .

Gordan

Found this on Youtube - is this it?

http://www.youtube.com/watch?v=5B0V07iE5uw

CMadatMe

Yes thank You

Thanks Gordan, thats it..As you can see gas valve reacts not rpm speed.  Like I said totally different animal then air fuel ratio. Gas is independent of air and air independent of gas. No other mod/con to the best of my knowlegde has or is using this technology.

Gordan

I believe Weisshaupt is using it.

Not a well-known or available brand this side of the big puddle, tho.





I'm not sure that my interpretation of that animation is the same as yours, though - for what that's worth. Output is still modulated via combustion fan speed. Air-fuel ratio is modulated via gas valve, but it still appears to be a neg-reg venturi, it's just that it has a "throttle screw" that's adjusted automatically. I think that's pretty much what croydoncorgi was saying. Then the only point of contention is when that automatic throttle adjustment occurs - continuously (not sure I'd see the benefit of that except perhaps to better tune the a-f ratio to various output points than is possible with a venturi alone?), once per cycle, periodically?

croydoncorgi

If in doubt - ask....

Gordan summarises neatly what I've been saying about how the Viessmann burner system works.



I called Viessmann technical department  in UK today:

- yes - it's a zero-pressure regulator,

- no - the burner controller does NOT adjust the gas mix all the time according to ionization current.  The tech thought it only happened on burner start.  And for the measurement to work, the burner needs to be on full power for a while.

- and perhaps most important, it is fan RPM (only) that regulates the burner output.



The video is correct but it never says HOW OFTEN the process takes place.   It only shows the part of the gas valve that is adjusted by the Lamda system.  The effect of that adjustment is to change the 'zero-pressure' and therefore the gas/air ratio.  The new setting will then last until it's changed again.



And in the real world, how often does gas quality actually change?   Not often - so no need to tweak the mix frquently / continuouosly.