1
Q
What are the mandatory requirements for rating plates on a gas furnace? (9)
A
- certification agencies stamp
- type of fuel
- altitude approved for
- max input rating
- max inlet pressure
- manifold pressure
- electrical rating
- Manufature name
- model number
2
Q
What is optional requirements for a furnace rating plates?
A
- orifice
- output
- serial number
3
Q
What are the installers responsibilities (3)
A
- ensure the appliance is in safe working order
- instruct the user in the safe and correct operation of equipment installed
- ensure manufacture instructions supplied are left with the user
4
Q
Who is considered the installer?
A
the last person to work on the appliance
5
Q
What is the purpose of a gas burner?
A
- deliver a gas and Air mixture to the combustion zone for ignition
- mixes the gas and Air together for ignition, proper adjustment is essential
6
Q
What are the two types of burners?
A
- atmospheric burners
- forced draft/power burners
7
Q
What is the difference between an atmospheric burner and a forced air/power burners?
A
- atmospheric burners rely on difference in atmospheric pressure for combustion
- forced draft or power burners uses a mechanical device (fan) to deliver air for combustion
8
Q
What is the Venturi Principle?
A
- As the gas stream comes through the orifice, air is drawn in and through the primary air openings into the mixer head
- the gas mixes with the fuel in the mixing tube (Venturi)
9
Q
What is the calorific value and Air to gas ratio for natural gas?
A
- 1,000 BTU/cuft
- 10:1 ratio
10
Q
What is the calorific value and Air to gas ratio for propane?
A
- 2,500 BTU/cuft
- 24:1 ratio
11
Q
What is a non-aerated burner?
A
- luminous
- gas is supplied to the combustion area without being mixed with air before it is ignited
12
Q
What is an aerated burner?
A
- Bunsen
- the air mixed with the gas upstream of the point of ignition
13
Q
How are burners categorized?
A
by how the air is mixed with the flame
14
Q
What is an oxidizing flame?
A
- large amounts of primary air
- hard, sharp flame
15
Q
What is a neutral flame?
A
- medium amount of primary air
- medium sized flame
16
Q
What is a carbonizing or carburizing flame?
A
- small amount of primary air
- soft, large flame
17
Q
What is in inshot burner
A
Horization manner
18
Q
What is an upshot burner
A
Largely verticle
19
Q
What are causes for a yellow tip flame?
A
- not enough air/airflow
- too little primary air
- primary air openings clogged
- burner ports blocked
- misaligned or dirty orifices
- blocked flue
- orifice too large
20
Q
What are the causes for a lifting flame?
A
- too high velocity
- too much primary air
- burners overfired
- orifice too large
- orifice partially blocked
21
Q
What are the causes for a waving blue flame?
A
- draft/air blowing on burner
- excessive draft around burner
- cracked heat exchanger
22
Q
What are the causes for main burner flame to be too large?
A
- too much gas
- burners are overfired
- defective regulator
- burner orifice too large
23
Q
What are the causes for flashback?
A
- not enough gas pressure
- too much primary air
- burners underfired
- one orifice too large or too small
- gas valve leaking
24
Q
What are the causes for a noisy flame?
A
- too high velocity
- too much primary air
- pilot overfired
- burr in orifice
25
What would be considered a normal burn? ""hint: inches/second)
when gas/Air mixture speed is at 26"/second
26
What is considered a lift off burn? **hint: inches/second
when gas/air mixture speed is at 36"/second
27
What is considered a flashback burn? **hint:inches/second
when gas/air mixture is at 24"/second
28
What are pilot and pilot burners used for?
to effectively ignite main burners on appliances
29
What are the four main categories of pilot burners?
- continuous
- expanding
- intermittent
- interrupted
30
What is a continuous pilot burners?
standing pilot, 24hrs a day
31
What is an expanding pilot burners?
hybrid of a standing pilot, pilot gas supply is increased to effectively light the main burner
32
What is an intermittent pilot burners?
only ignited when there is a call for heat. remains on during the call for heat
33
What is an interrupted pilot burners?
only ignited when the is a call for heat. extinguished once main burners is lit
34
What is direct ignition?
ignites by direct spark or hot surface ignition
35
What are the three main types of pilot burners
- aerated
- post aerated
- non aerated
36
What is the main objective when igniting the main burners?
- achieve the bluest flame possible and avoid soot/carbon residue
37
What is an aerated pilot
- AKA Bunsen or linting pilot
- primary opening is susceptible to blockage by lint or dust
38
What are non aerated pilots?
- AKA non primary or non linting pilots (used on gas dryers)
- slight yellow flame as there is no primary flame
39
What are post-aerated pilots
- AKA incinerating or target pilots
- commonly used in residential and light commercial
- similar to aerated pilots; has primary air openings which burns off lint or dust in the air
40
What is a safe hookup (proved pilot)
- AKA non 100% shut off
- automotive safety control is limited to the main burner
- on pilot outage, the main burners gas is shut off by the safety control but pilot gas is not
41
What is a 100% safe hook up (pilot proved)
- most appliances are of this type
- the automatic safety control shuts off the gas supply to both the main burners and the pilot in case of pilot outage or safety control failure
42
What is the Seebeck effect?
when two different metals joined at both ends and heated at one ends creates a small amount of DC current flow
- measured in Millivolts DC
43
What are thermopiles?
- AKA powerpiles
- several thermocouples linked in series
- replaces the same millivolt output that was removed
- 325 to 750mv DC
44
What is the power unit?
energized by the thermocouple or thermopile and holds open the safety gas valve or safety switch closed
- always replace with same millivoltage output
45
When installing a pilot
it should not be mounted too high above or too low beneath the burner....just right
46
How to ensure most amount of voltage is produced by the thermocouple?
ensure there is a difference between the hot and cold junctions
- heat the top 3/8" to 1/2" tip
47
What to avoid when installing the thermocouple?
BENDING!! avoid bends closer than 1" and never closer than 1/2"
48
When testing thermocouples, what rating should you get for an open and closed circuit?
open circuit: 17 - 32mv DC
closed circuit: 8 to 17mv DC
49
When testing thermocouples, what ratings should you get for drop out range and turn down test?
Drop out range: 0.75 - 6mv DC
Turn down test: 2mv DC
50
What is the typical thermocouple testing?
- between 25-30mv DC
51
What are the 3 types of orifices
- fixed orifice/plug orifices
- adjustable orifice
- cap/universal orifices
52
What is the most common type of orifices?
- fixed/plug orifice
53
What is an adjustable orifice?
- used one older gas ranges, some industrial burners
54
What are cap/universal orifices?
- also used on fuel appliances that need to be site adjusted to burn propane or natural gas
55
What does an orifice do?
- controls the volume of gas delivered to the burners
56
How are orifices sized?
- DMS (Drill manufacturers Standard)
- the larger the DMS number, the smaller the orifice size
57
What can cause problems with orifices?
- correctly installed orifices present no problem
- problems occur when changing fuels (natural gas to propane) or altitude (sea level to 4500')
58
What MUST be considered when drill orifices?
- always drill 2 sizes smaller than desired; adjust with a reamer
59
What must be determined when sizing and orifice and calculating input rates?
BTUH rate must be determined first
60
What is orifice interpolation?
finding the BTU value between two given pressures on the chart
61
Why altitude adjustments are needed when sizing an orifice?
- altitude affects combustion due to air pressure
- air is thinner at higher altitudes therefore gas volume must be reduced
- appliances are required to have altitude ratings marked on the rating plate
62
What is considered sea level and high altitude elevations?
sea level = 0' to 2000' elevation
high altitude = 2000 to 4500' elevation
63
When installing appliances at high altitude, what must be done? At above 4500'
at high altitude, derated by 10%
above 4500', derated by additional 4% per 1000' elevation rise
64
What is the purpose of a regulator?
reduce and maintain a set pressure while compensating for demand changes
65
How does a regulator work?
it uses a fixed orifice opening for the restricting element, a diaphragm for the measuring element and a spring for the loading element
66
What are restricting elements in a regulator?
- orifices and the valve plug
- the restriction limits the amount of maximum flow capacity through the regulator
- the office is fixed while the valve plug moves
67
What is the measuring element in a regulator?
- the diaphragm
- made of neoprene
- attached to the valve stem and measures outlet (downstream) pressure
68
What is the loading element in a regulator?
- the spring/weight
- by increasing or decreasing the spring tension acting on the diaphragm, you can raise or lower the outlet pressure
- dial in (clockwise) to increase
69
What is a regulator vent?
- (spring/weight)
- atmospheric pressure must be allowed to and from the spring housing
- terminate outdoors (unless limiting)
70
What are internal relief devices in a regulator?
- over pressure devices to relieve excess gas pressure
- if outlet pressure rises too high, excess pressure is vented to outdoors
71
What are leak limiting controls on a regulator?
- ball check leak limiting devices
- restrict max amount of gas vented (2.5cuft/hr for natural gas)
- if diaphragm ruptures ball check closes
72
What is a low pressure trip in a regulator?
- a low pressure trip activates if outlet pressure becomes too low
- reset by pulling plunger underneath dust cap
73
What are some causes for a low pressure trip on a regulator? (3)
- low inlet pressure,
- rupture in outlet piping, - improper operation of gas equipement
74
What are the different types of regulators?
- service regulators
- system regulators
- appliance regulator
- servo regulators
75
What is a service regulator
- service to a building (only utility company can work on)
76
What is a system regulators?
- used to decrease building pressure before going to appliances
77
What is an appliance regulator?
- found in appliances
78
What is a servo regulator?
- combination gas valve
79
How many regulators is used on a propane system?
2 regulators or a dual stage regulator to achieve manageable pressures
(1 high pressure regulator at the tank = 5 to 10 psi and 1 low pressure regulator outside the home = 11 to 14 inches w.c)
80
What is the code for venting a regulator?
- low pressure trip or relief valves must not be isolated or bypassed, no plugs of caps on the vent terminal
- vent termination must be at least 3' from a dryer vent
Period 2 - SAIT
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