Protective Instrumentation and Shutdown Devices – High Fuel Pressure
Firebox installations must be designed to minimize the probability of flame failure.
• For gas burners this is done by installing reliable fuel systems and reliable minimum-fire bypasses.
• For oil burners this is done by installing reliable oil systems and maintaining reliable gas flames at each operating burner. (The gas flame heat release should be at least 10% of the oil burner design heat release. Having oil flames at some burners with gas flames at other burners does not meet this criterion.)
If these criteria are not met, then low-pressure shutdowns, which sense the fuel pressure in the burner header, are recommended.
Finally, if these are impractical, then flame failure shutdowns are recommended. Such shutdowns should occur automatically; operator response to a flame failure alarm is too slow to avoid accumulating a hazardous amount of fuel in the firebox.
The recommended flame scanner is the Honeywell C7076 ultraviolet scanner with a self-checking feature. It can also be obtained with a one-second power loss override to avoid shutdowns due to power dips. Recently most installations have included a source of uninterruptible power for the flame scanners. The scanners should have adequate weather protection and may require air-purged sight tubes.