Frequent Flame Scanner Failure 1

[EEENGRX]

I keep having frequent trips of the scanner in the SRU unit. What are some of the reasons why a flame scanner would trip many times with respect to the mentioned unit and also in general? I do have some ideas but the more ideas and solutions I have would be very useful.

 

[3DDave]

If you tell what you already know it will save you then making the inevitable "I already know that" response and it will save others from typing those replies you will dismiss.

 

[georgeverghese]

The OpCo I used to work for has a clear preference for burner flame scanners on furnaces / heaters:

Main Flame : UV type - Perpel and Fuchs(if I remember correctly)
Pilot flame : IR type - dont remember make/model.

Main flame trip is initiated by 2oo3 voting on scanners for each burner
Pilot flame trip voted 1oo2 for each

Suggestion: Call the experts at Perpel&Fuchs.

 

[EEENGRX]

Thanks for the responses

 

[EEENGRX]

So the issue in contention is that the Flame scanner lens keeps getting dirty which is a direct cause for most of the trips? Any suggestions as to what may be causing this trend?

 

[waross]

Years ago I was involved with a heater that cycled off at times.
When started, the controls had 7 seconds to see a flame before tripping off.
I added an alarm for no flame at 4 or 5 seconds.
If the "Slow Light-off" alarm came up, maintenance would wipe the scanner lens.
End of unexpected trips.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[EEENGRX]

Thanks but what would typically make the lens get dirty on a frequent basis wrt an SRU unit?

 

[waross]

Soot from incomplete combustion.
Most often an issue during starting/light-off.
or
A badly adjusted air damper and resulting less than optimum air fuel mixture.
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[EEENGRX]

Thanks for the solid response. What do you think about changing the position of the scanner to improve line of sight?

In addition, there has been a few times when it goes in and out of alarm and when scanner is checked, the lens aren’t dirty.Any thoughts?

 

[waross]

In addition, there has been a few times when it goes in and out of alarm and when scanner is checked, the lens aren’t dirty.Any thoughts?

Here's a thought; (Grin)

What do you think about changing the position of the scanner to improve line of sight?

Good idea.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[georgeverghese]

My memory on this topic seems to be fading away, but I recall there are 2 reasons for providing an instrument air purge at the main flame scanner
a) to keep the scanner cool
b) keep the flame scanner lens clean

 

[pmover]

The flame scanner needs to have a source of purge air at a pressure greater than firebox pressure. The purge air should enter the tube/pipe where flame scanner is installed just downstream of scanner glass face.

Purge air could be instrument air, fan pressure from fan housing, etc.

If instrument air, be sure the instrument air is purging the scanner tube/pipe before ignition.

If fan, ensure sufficient fan pressure before ignition.

The purge air also keep flame scanner cool.

 

[EEENGRX]

Thanks. This is an SRU unit and Nitrogen is used in purging