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Furnace Commisioning > Standard Furnace Components > Flashcards

Standard Furnace Components Flashcards

1
Q

Max temp of a furnace by code

A

250f°

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2
Q

Components of a low efficient furnace

A

Heat exchangers
Gas valve
Draft hood
Burners
Hi-limit
Combination fan limit control
Pilot assembly
Transformer
Thermostat
Flame rollout switch
Draft spill switch
Motor
Manifold orifices
Capacitors

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3
Q

What is the fan on temp range
What is the fan off temp range
What is differential temp

A

120f°(49c°)-140f°(60C°)
90f°(32C°)-100f°(38C°)
Min 35f° (19c°)

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4
Q

How many millvolts are used in a thermocouple

A

20-30milvolts

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5
Q

What changes the rotation of a belt motor

A

Reverse the wires under the cover plate

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6
Q

Type of capacitors
What do they do

A

Run capacitor
Start capacitor
Hold electricity and starts the furnace process

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7
Q

Furance sequence of operation

A
  1. T-stat calls for heat (R and W closes)
  2. gas valve opens/energized
  3. Pilot light ignites burners
  4. Fan control turns on
  5. Blower motor energized
  6. T stat satisfied
  7. R and w opens
  8. Gas valve de energized
  9. Burners extinguish
  10. fan-off temp reached
  11. Blower motor de energized
  12. Stand by
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8
Q

Manifold pressure

A

3.5” W.C.

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9
Q

Configurations of furnaces

A

Up flow, down flow, horizontal, all positions

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10
Q

What switch measures temp once heat exchanger is warmed up

A

Fan switch or fan control

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11
Q

When T-stat is satisfied, what happens

A

Turns off electrical circuit to gas valve
“De-energized”

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12
Q

Furance operation process is called what?

A

Heating cycle

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13
Q

Controls used to operate furance are called. What are they

A

Operating controls
Thermostat, fan control,transformer,gas valve, and motor

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14
Q

Controls to make sure the operation is safe are called?
What are they?

A

Safety controls
Limit switches and thermocouple/ therompile

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15
Q

What is a standing pilot
Variations of pilot

A

Is a small flame that burns 24/7 located near main burner
Aerated, post-aerated (most common), and non aerated

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16
Q

If the pilot is out of alignment, what can happen
What is it called

A

Gas flows to burner to long and accumulates. When it does ignite causes small explosion.
Delayed ignition

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17
Q

What is a thermocoupler

A

Thermal electric device made of two dissimilar metals (iron and constantan) produces a small voltage 20 to 30 millvolts AC

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18
Q

How much should the flame encompass the tip of a thermocouple.

A

⅜” to ½”

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19
Q

What is a thermopile, also known as

A

Thermocouples wired in a series
Power piles and pilot generators

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20
Q

how does a power unit work

A

If the power unit isn’t getting power from the thermocouple/pile, the electromagnet in it will close the plunger, preventing gas flow.

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21
Q

What is the setting on the heat anticipator attached too

A

Amp draw of low voltage circuit (current draw of control unit to which the Thermostat is installed)

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22
Q

What class equipment is a transformer

A

Type 2

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23
Q

What do transformers operate by

A

Magnetic induction

24
Q

If the secondary has less windings then the primary it will have more or less voltage? What is this Transformer called

A

Less voltage, a step down Transformer

25
Q

2 types of blower motors

A

Belt drive, direct drive

26
Q

What do Draft diverters or draft hoods do

A

Provide a pressure balanced flue. Breaks the stack action while at the same time prevents down drafts.

27
Q

Furnace Rating plates will have what information

A

Orifices sizes, information on approval agency,altitude rating (listed as sea level) input and out rating of appliance and fuel type

28
Q

3 bimetal temperature sensing devices

A

Strip, spiral and disc

29
Q

Main purpose of a limit switch

A

To shut down the gas supply, should the furnace get too hot

30
Q

List the different furnace configurations

A

Upflow,downflow, horizontal, and all position

31
Q

Why is a Tstat better for controlling the furnace than a light switch

A

They can monitor the temperature and respond by turning off or on equipment.

32
Q

Once there is a call for heat in a furnace, what happens

A

Complete an electrical circuit that energizes the gas valve allowing gas to flow.

33
Q

A combination gas valve consists of?

A

Regulator
Manual ON/OFF/pilot valve
Control circuit connections
Pilot gas adjustment
Thermocouple connection
Power unit

34
Q

What is CW and CCW stands for what in regards to belt driven motors?

A

Clockwise and counterclockwise

35
Q

Regardless of hp rating, all belt drive motors rotate at what?

A

1725 rpm

36
Q

While most belt driven motors are single speed(1725rpm), there are two speed motors. What rpm is the low speed

A

1140rpm

37
Q

Different between belt and direct motors

A

Direct drive doesn’t have a belt it is mounted directly to the fan unit

38
Q

Direct drive motors have up to how many speeds

A

5

39
Q

What are most motors in furances called

A

Squirrel cage induction motors gets name from fan wheel

40
Q

Fans used in furnaces are ____ type fans with____curving blades

A

Centrifugal, forward

41
Q

If the fan wheel is installed backwards what can happen

A

Furnace may overheat and be shut off by limit switch

42
Q

Shaft size of a belt driven fan

A

¾”

43
Q

What happens when adjusting the pulley of a belt drive fan

A

If the pulley is adjusted in, the diameter becomes larger, and fan speed increases.
If the pulley is let out, the diameter will be smaller, resulting in decreased air

44
Q

Direct drive fan shift size

A

½”

45
Q

What do heat exchangers do

A

Transfer heat from burners to the air stream.

46
Q

Heat exchangers can be what 3 styles

A

Clam style, barrel style, or tubural

47
Q

What happens if down draft enter venting system?

A

Could interfere with the burners or extinguish pilot light

48
Q

What is the venturi effect

A

the reduction in fluid pressure that results when a moving fluid speeds up as it flows through a constricted section (or choke) of a pipe

49
Q

What happens when manifold pressure is increased or reduced

A

If increased will cause more air to enter burner resulting in flames lifting off burner
If reduced, then air gas mixture is reduced, and flashback will occur

50
Q

The venturi tube is also called? What does it do

A

The mixing tube
Mixes the gas and air for the burner through high speed low pressure

51
Q

Inside the heat exchanger, heat from burners transfer through what process?

A

The heat from burners transfers through convection and radiation up the metal surface of the

52
Q

What is the job of a burner

A

Transforming a combustible fuel into heat

53
Q

Two types of burners

A

Upshot and In-shot

54
Q

Can you just resize the orifice size? What about converting to a different gas

A

Under no circumstances should you. If furance is to be converted from one gas to another, you can install a factory conversion kit only.

55
Q

Purpose of the flame rollout switch

A

The flame rollout switch is a safety feature that shuts off the gas supply to the burner if the flame blows out.

56
Q

What common voltage, used in furnaces, is found on the secondary side of a transformer?

A

24V

Furnace Commisioning (6 decks)

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