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Revision Notes > Module 11 Gas Safety Devices and Controls > Flashcards

Module 11 Gas Safety Devices and Controls Flashcards

1
Q

Which module covers gas safety devices and controls?

A

11

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2
Q

Gas Safety Devices and Controls fall all fit into the following objectives

  1. Safety
  2. Comfort
  3. Economy

Name three safety features

A
  1. Appliance ignition
  2. Flame failure safeguard
  3. Protect from excessive pressure and/or over heating
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3
Q

Gas Safety Devices and Controls fall all fit into the following objectives

  1. Safety
  2. Comfort
  3. Economy

Name one economy feature

A

Max heat input to prevent bad combustion or overheating

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4
Q

What is the correct term for a Flame Failure Device (FFD)?

A

Flame Supervision Device (FSD)

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5
Q

Which one is not a thermal FSD?

a. Bi-metal strip
b. Liquid Expansion
c. Flame rectification
d. Thermo-electric

A

c Flame rectification

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6
Q

Bi-metallic strip – explain how works?

A

Two metals with dissimilar expansion rates bonded together.
When heated different rates cause it to bend.
This bend opens / closes the valve

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7
Q

If a bi-metallic strip fails what is the risk?

A

Valve does not shut – known as a fail to danger

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8
Q

Liquid expansion devices – commonly found in modern …

A

Cookers and water heaters

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9
Q

When an oven is turned on the pilot light of bypass flame heats the liquid expansion valve and what happens?

A

Liquid vaporizes, expands lots down the capillary tube, bellows on expands, valve opens on main gas = full flame

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10
Q

If a liquid expansion valve fails is it:

a. Fail safe
b. Fail to danger

A

a. Fail safe

Vale shuts

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11
Q

What controls the temperature of an oven?

b. Liquid expansion valve
c. Thermostat

A

c. Thermostat

LEV confirms the presence of the flame. It is either on or off!

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12
Q

How do you test a Liquid Expansion Valve is working

A
  1. Turn oven to max – bypass flame, ~30 seconds later full flame
  2. When oven at correct temp. flame drops to low
  3. Turn off oven, wait 30 seconds, relight.
  4. Flame on low – passed
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13
Q

Often a thermocouple energizes an ….
which holds open a valve and lets the gas flow

A

Electro-magnetic unit

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14
Q

What metals are typically used in thermocouples?

A

Chrome-nickel alloy and copper

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15
Q

When a thermocouple is heated an electromagnetic force (EMF) is produced which energises the magnet. What voltage do these two metals produce?

A

15 to 30mV

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16
Q

As a guide how long should it take for a thermocouple to become energized?

A

~45 seconds

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17
Q

How do you test that a thermocouple is working?

A

1) Running at op temp
2) Turn of gas either by service valve or ECV
3) Start stop watch – listen for valve to close
4) Tightness / let by test either at pressure test point on appliance or the meter

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18
Q

FSD – maximum time allowed for a DFE to shut down:

a. 60 seconds
b. 90 seconds
c. 120 seconds
d. 180 seconds

A

c) 120 seconds

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19
Q

FSD – maximum time for non DFE fires to shut down:

a. 60 seconds
b. 90 seconds
c. 120 seconds
d) 180 seconds

A

d) 180 seconds

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20
Q

FSD – maximum time for circulators, cooker, hotplates and grills, refrigerators and storage water heaters below 8kW:

a. 60 seconds
b. 90 seconds
c. 120 seconds
d. 180 seconds

A

b. 90 seconds

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21
Q

FSD for all other appliances:

a. 60 seconds
b. 90 seconds
c. 120 seconds
d. 180 seconds

A

a. 60 seconds

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22
Q

What type of FSD is shown in the picture

A

Flame rectification

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23
Q

Does flame recitation

a) fail safe
b) Fail to danger

A

a) fail safe

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24
Q

Carbon (soot) is a great conductor. If there is a build up between the electrode and the burner will a flame rectification unit:

a) fail to danger
b) Fail to safe

A

a) fail to safe

Why?

Allows AC to follow around the circuit. No DC = shuts down

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25
Q

Flame rectification is commonly found in:

a) o/f boilers and LFE fires
b) Gas wall heaters
c) Fanned flue appliances and pre-mix burners

A

c) Fanned flue appliances and pre-mix burners

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26
Q

Flame rectification circuits can be tested by

a) turning off the electrical supply to the appliance
b) Turning off the gas supply
c) Disconnecting the igniter

A

b) turning off the gas supply

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27
Q

In a flame rectification circuit what type of current is used?

a) AC
b) AC & DC

c) DC

A

b) AC & DC

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28
Q

Flame rectification, how does the AC get converted to DC?

a) a rectifier in the igniter
b) a rectifier post the burner
c) the gas

A

c) the gas

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29
Q

Which type of flame conducts electricity the best?

a) luminous
b) blue flame

A

b) blue flame

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30
Q

Which is the best conductor of electricity?

a) carbon
b) Copper
c) blue gas flame

A

b) copper

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31
Q

With part of a pre-aerated flame conducts electricity the best?

a) inner cone
b) outer cone
c) outer mantle

A

b) outer cone - the blue bit!

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32
Q

To optimise a flame rectification circuit the positive plate (the igniter) and the negative plate (the burner) must be

a) the same size
b) igniter x 4 > burner
c) burner x 4 > igniter
d) igniter x 10 > burner
e) burner x 10 > igniter

A

e) burner x 10 > igniter

By having one plate a lot larger than the other the current goes one way or is rectified!

Another explanation:

Normally an AC current is BIG one way and BIG the other. DC BIG one and SMALL the other. Smaller igniter, big burner, electrons don’t want to return, becomes DC

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33
Q

If a flame rectification circuit keeps locking out how could you test it?

A

Check amps, see attached

!! Figure 7, page 12!!

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34
Q

What is a VSD?

a) Visitation Sensing Device
b) Vittles Sensing Device
c) Voiding Sensing Device
d) Vitiation Sensing Device

A

d) Vitiation Sensing Device

35
Q

With a VSD the flame lifts off as

a) Carbon dioxide levels fall
b) Oxygen levels fall
c) Nitrogen levels fall

A

b) Oxygen levels fall

36
Q

VSD - explain what is happening in the pictures

A
37
Q

Alternative names for VSD are

a) atmosphere sensing device (ASD)
b) oxygen depletion sensor (OSD)
c) oxygas pilot (OP)
d) All of the above

A

d) All of the above

38
Q

If a VSD keeps ‘going out’ which are possible causes?

a) Damage
b) Incorrectly located
c) Lint in aeration port
d) Abnormal flue or vent conditions
e) All of the above

A

e) All of the above

39
Q

Faults on cooker burner controls are often due to what?

A

Drying out of the lubricant

40
Q

The correct lubricant for gas taps is:

a) Vaseline
b) Molybdenum disulphide grease
c) Silicone grease
d) Any of the above

A

b) Molybdenum disulphide grease

41
Q

Where do you commonly find a safety cut off valve?

A

1) Cooker lid
2) Oven door when there is a grill inside

42
Q

What is an SSOV?

A

Safety Shut Off Valve

43
Q

A primary thermostat is located in the appliance, where would a secondary thermostat be located?

A

Remotely, good example is a room thermostat.

44
Q

Primary and secondary thermostats can be subdivided into:

a) metallic and non-metallic
b) liquid and vapour
c) mechanical and electrical
d) All of the above

A

c) mechanical and electrical

45
Q

Name components on this mechanical oil filled thermostat

A
46
Q

Outline how you would test an oven thermostat

A

1) turn oven on to mid point (GM 5)
2) Has FSD energised and burner gone to main flame?
3) Wait ~15 mins for oven to warm up
4) Burner should reduce to low but not go out

47
Q

An electrical thermostat has

a) gas passing through the unit
b) No gas passing through the unit

A

b) No gas passing through the unit

48
Q

To control the gas flow an electrical thermostat uses:

a) bellows
b) diaphragm
c) solenoid

A

c) solenoid

49
Q

Solenoid valves open and close due to:

a) an electrical current
b) change in temperature
c) change in gas pressure

A

a) an electrical current

50
Q

When the current flows in the coil of a solenoid valve the armature is :

a) drawn into the tube, closing the value
b) pushed out of the tube, opening the valve
c) drawn into the tube, opening the valve

A

c) drawn into the tube, opening the valve

51
Q

Solenoids using AC supplies are often noisy due to the reversal if the current causing the armature to vibrate against the pole. This can be solved by:

a) lowering the voltage
b) using a rectifier
c) turning off the supply

A

b) using a rectifier

52
Q

When testing a solenoid the electrical supply is isolated and you:

a) listen for the valve to close
b) do a tightness test
c) All of the above

A

c) All of the above

Listen and measure for pressure loss

53
Q

A medium and low pressure regulator is used when the supply pressure is:

a) between 75 mbar and 2 bar
b) 21 mbar
c) >2 bar

A

a) between 75 mbar and 2 bar

54
Q

What does UPSO mean?

A

Under pressures shut off

55
Q

The picture below is a thermoelectric FSD. Name the two key things that identify it

A
  1. Push button
  2. Termocouple
56
Q

Thermoelectric FSD – outline test method

A
  1. Light pilot and establish

  1. Turn gas off, time until lcoks out
57
Q

What type of device is shown in the picture?

A

Bi-metallic strip FSD

58
Q

How do you test a bi-metallic strip?

A
  1. Light pilot and establish
  2. Turn pilot off, time until burner turns off
59
Q

What device is shown in the picture

A

Vapour pressure FSD

60
Q

How do you test a Vapour pressure FSD?

A
  1. Light burner (should light on low flame) after approx. 30sec rising to high flame.
  2. Turn gas tap off, wait for 90 sec and re-light (should light on low flame)
61
Q

Where do you find vapour pressure FSDs?

A

Ovens

62
Q

How do you test flame rectification devices?

A

Turn appliance on, make sure flame lights and establishes
Keep the demand on the appliance and turn the gas off. The appliance should go into lockout or keep sparking

63
Q

What device is shown in the picture and key thing that identifies it:

A

Mechanical thermostat (vapour expansion)

Dial with numbers indicated

64
Q

Where are mechanical thermostats (vapour expansion) commonly found?

A

Ovens

65
Q

How do you test a mechanical thermostat (vapour expansion?)

A
  1. Turn oven on and heat up for 15 min.
  2. Turn control to lowest setting flame should drop to by-pass rate
66
Q

What device is shown in the picture and key thing that identifies it:

A 
Mechanical thermostat (rod type)
 Dial with numbers indicated
67
Q

Name two places where you would find a mechanical thermostat (rod type)?

A
  1. Old cookers
  2. Old water heaters
68
Q

What device is shown in the picture and key thing that identifies it:

A

Electrical Thermostat

69
Q

How do you test an electrical thermostat?

A

Heat up appliance, thermostat should turn the solenoid off or modulate the burner pressure down

70
Q

What is the purpose of a solenoid?

A

An electrically operated gas valve

71
Q

How to you test a solenoid

A
  1. Turn electricity on valve opens
  2. Turn electricity off valve closes
72
Q

What device is shown in the picture?

A

Multi-function control valve

73
Q

How do you test a multi function control?

A

If the FSD, Regulator and solenoid work then the multi-function control is working.

74
Q

What device is shown in the picture?

A

Gas tap

75
Q

How do you test a gas tap?

A
  1. Tap locks in the off position
  2. Tap functions correctly
76
Q

What device is shown in the picture?

A

Atmospheric Sensing Device (ASD or VSD)

77
Q

What is the purpose of an ASD?

A

To close down the open flued appliance automatically, if the appliance and flue operate incorrectly

78
Q

What device is shown in the picture?

A

Atmospheric Sensing Device / over heat thermocouple interrupter

79
Q

What is the purpose of an Atmospheric Sensing Device / over heat thermocouple interrupter?

A

To close down the open flued appliance automatically, if the appliance and flue operate incorrectly

80
Q

What device is shown in the picture?

A

Zero governor

81
Q

What is does a zero governor do?

A

To compensate for the negative pressure caused by the fan, on the gas valve (this could pull more gas into the burner than intended)

82
Q

How do you test a zero governor?

A

Attach manometer to burner pressure test point Turn appliance on when the fan comes on the manometer reads negative pressure, quickly going to positive pressure when the burner comes on.

83
Q

What device is shown in the picture?

A

Modulating multifunctional control valve

Revision Notes (26 decks)

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