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What are the four main types of pilot burners and how do they differ?
Continuous: always on, inefficient, e.g. water tanks
Expanding: flame reduces after main lights, e.g. ovens
Intermittent: on with main, off with main, e.g. fireplaces
Interrupted: shuts off once main is proven, e.g. boilers
What are the two modern ignition systems and their advantages?
Direct spark ignition
Hot surface ignition
• Silicon carbide: 110V, don’t touch (finger oils cause hot spots)
• Silicon nitride: more durable, tolerates contamination
What are the three types of pilot flame systems?
Aerated: blue flame, uses primary air, aka Bunsen-type
Non-aerated: yellow flame, uses only secondary air, used in dryers/ranges
Post-aerated: no mixing tube, resists lint, common in residential/light commercial
What are aerated pilot details including orifice colors?
Air and gas mix before combustion
Flame is blue
NG orifice is silver
Propane orifice is dark brass
What are the installation requirements for a pilot under B149.3-20?
Must be visible and safely lit
Correctly positioned relative to the main burner
Protected from dirt, scale, and falling debris
Not exposed to drafts (shielded if needed)
Must not be impinged by main flame
Must reliably light the burner under all conditions
Must be properly secured
What are the purposes of a pilot and when is a proved pilot required?
Lights the main burner
Activates flame failure device
Proved pilot required on all automatic appliances
Unproved allowed only on manual appliances (e.g. BBQ, bunsen burners)
How quickly must a pilot light the main burner and what happens if it doesn’t?
Within 4 seconds
If not, reposition the pilot
Do not upsize the flame (can overheat thermocouple)
Why might a pilot have multiple flame tips?
To ensure the flame contacts both the thermocouple and flame rod
What is the Seebeck effect and what materials are used in thermocouples?
Heat applied to two dissimilar metals generates DC millivolts
Positive leg: nickel alloy
Negative leg: constantan
Common type: Type J
What is a thermopile and how does it function?
Multiple thermocouples in series
Generates 250–1000 mV
Powers safety and control valves
Self-energizing (no external power)
What are the installation guidelines for thermocouples and thermopiles?
Don’t bend within 1 inch of junction
No joint compound needed
Flame should touch top 3/8 to 1/2 inch
Voltage should read between 17–32 mV
What is the correct flame envelope size for a flame rod?
Flame should be 4 times the grounding surface area of the rod
What is a safe hookup and when is it allowed?
A non-100% shutoff system
Shuts off main burner but not pilot gas
Allowed only for lighter-than-air gases (e.g. natural gas)
Why are safe hookups not allowed for propane?
Propane is heavier than air and may accumulate
100% shutoff system is required
What does a 100% shutoff safety system do?
Shuts off both pilot and main gas if flame fails
What does the gas code say about bleed tubes on diaphragm valves?
Must terminate at pilot or thermocouple
Flame must not be sensed by flame detection element
What is an Energy Cutoff (ECO) switch and what is its purpose?
High-temperature safety switch
Shuts off 100% of gas under abnormal heating
May replace temperature relief device (pressure relief still required)
Typical limit: 200–210°F