Flame failure electrode question

My old White Knight gas tumble dryer played up the other day and I found that the earth electrode (immediately above the main electrode) had eroded and sagged until it was touching the central electrode. I bent it back and all was well (briefly - but that's another story).
I thought I ought to order a new electrode but White Knight tell me that my type (with integral earth electrode) has been superceded by one without an earth electrode.
I'm sceptical that this will work in my machine (in the absence of an earth) but I could be wrong.
Here's what mine looks like.
http://www.zen31010.zen.co.uk/images/ffe.jpg
The replacement is just the same but without the "hockey stick" earth electrode.
I'm waiting to hear from the technical adviser at the moment.
Should I just try it or is my scepticism justified?
Tim
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Looks exactly like the ignition electrode in my Keston boiler. They failed as the earth electrode drooped and the gap became too big (it's mounted up the other way in the boiler's downward pointing burner). They then modified them, and so far, the new type has been OK (I can't remember what changed - I think the ceramic sleeve became longer, but it still has the two electrodes).
I did repair the old ones a couple of times by bending the electrode back, but this has to be done with it hot - if you try bending it cold after it's had lots of heat treatment in the boiler, it's brittle and usually snaps.

Usually, the contact gap is resonably critical for proper ignition; too small or big reduces chance of successful ignition (and too big can also damage the spark coil). So it depends what the ground electrode will be and how far away it is.
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Andrew Gabriel
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It's not an ignition electrode, it's for flame sensing (hence subject!).
Tim
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harry wrote:

Well yes, I know that.

Um no, not in this case. There is a seperate flame detector elctrode.

Pilot light in a tumble dryer? I think not. ;-)
Anyway, for anyone who is interested, the technical bods from Crosslee have been on the phone and tell me that as long as the tip is within 22mm of the base of the burner, it will work without the earth electrode. Seems a little odd given that the old gap was 1-2 mm. I'm not in a hurry to change the electrode now though seeing as it's working.
Tim
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I'll bet many more house fires have been caused by electric dryers! ;-)
Seriously though, there are so many failsafes I doubt very much that a gas dryer is any more dangerous than an electric one.
They certainly seem to be more durable. 21 years old and still going strong.
Tim
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My first experience with tumble driers was a gas one (in my university hall of residence). Full washing load dry in 5 minutes (and that was probably after a spin at no more than 500RPM in top loading washer). Also used similar ones in the US more recently. Just have to be careful to check no one's melted a pair of trainers in them beforehand.
Electric ones were a tremendous disappointment when I first tried one. That's why I've never owned one.
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Andrew Gabriel
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On 10 Sep,

My first lasted about that long. (Support spider for drum failed, If I'd known I could get one at the time it would have been repaired). It was replaced by an almost identical one. Both White Knight.
Their service/spares dept is excellent in my experience.
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Good job I got back in time ...
No Harry, stick to your solar panels, you are completely wrong
It ABSOLUTELY doesn't measure the resistance, a flame acts like a lossy rectifier and the flame sense circuit is looking for that rectification effect in the flame - its a very safe way of flame detection since it depends on a parameter that can't easily be duplicated in the way that a resistance can
As long as the jet from which the gas issues is well earthed, then there is a circuit when there is a flame (assuming that the sense electrode is also in the flame)

But this isn't the case, is it? he said so

No - he's shown the old one as a single electrode, not a junction

Eejit
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geoff

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And you were prolly as incompetent then as you are now. I have vastly more experience on modern domestic gas appliances than you do
It's not industrial gas equipment, is it - we're talking about modern domestic gas appliances here. They don't use UV / IR , they rarely use thermocouples (and if you had a clue, it would be obvious from the sketch that it wasn't)

This "One implementation of a gas burner with auto reignition senses the electrical conductivity of the flame."
and this " There are also ionisation flame detectors, which use current flow in the flame to detect flame presence, ... " while not incorrect, are misleading and written by someone who doesn't understand the process - I do
Flame sense electrodes (in modern domestic gas appliances) work on detecting a rectification effect produced by the flame, they do NOT work on resistance
for example
http://contractingbusiness.com/feature/cb_imp_13002 /
"Flame rectification has become the primary means of flame sensing in virtually all new residential and commercial gasfired HVAC equipment. The days of the mercury filled autopilot and bimetal warp switch are long gone. Be it an intermittent pilot system, direct spark ignition, or a hot surface system, manufacturers have chosen flame rectification for their means of flame verification.
Why flame rectification? It may be the safest form of flame sensing available. It's virtually impossible to fool the ignition module with anything short of an actual flame simulator. It's very fast, with no cool down time such as with a thermocouple or autopilot. The gas flow can be stopped almost instantaneously. Any sensing circuit failure will result in a system shut down rather than an unsafe ignition."
So - you can piss off with your outdated and inaccurate claptrap. Half of your input to the thread was wrong, the other half (thermocouples and such) was just irrelevant
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geoff

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