Pilots, T/C, Thermopiles

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18 Terms

1
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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

2
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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

3
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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

4
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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

5
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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

6
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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)

7
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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)

8
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Why might a pilot have multiple flame tips?

To ensure the flame contacts both the thermocouple and flame rod

9
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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

10
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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)

11
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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

12
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What is the correct flame envelope size for a flame rod?

Flame should be 4 times the grounding surface area of the rod

13
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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)

14
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Why are safe hookups not allowed for propane?

Propane is heavier than air and may accumulate

100% shutoff system is required

15
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What does a 100% shutoff safety system do?

Shuts off both pilot and main gas if flame fails

16
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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

17
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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

18
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