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Plumbing Level 3 > F3: Switches and Relays > Flashcards

F3: Switches and Relays Flashcards

1
Q

What is the heart of operational systems?

A

Switches and relays

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2
Q

What is a switch?

A

a device that makes or breaks (aka closes or opens) a path in an electrical circuit to allow loads.

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3
Q

What is an example of a manual switch?

A

a light switch for a room

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4
Q

What happens when a switch is manually moved (aka thrown)?

A

The pole (moving part) changes

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5
Q

How are switches referred?

A

by the number of poles / throws they have

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6
Q

What is this?

A

Single pole, single throw switch

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7
Q

What is this?

A

Single pole, double throw switch

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8
Q

What is this?

A

Double pole, single throw switch

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9
Q

What is this?

A

Double pole, double throw switch

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10
Q

What is this?

A

7 pole (rotary) switch

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11
Q

What is a momentary switch?

A

a switch that must be pushed or tuned / held in order for the contacts inside to close.

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12
Q

Are momentary switches spring loaded?

A

Yes, snap open when released.

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13
Q

What type of switch is used to sense, measure / react to conditions (temp, pressure, flow, liquid level / position)

A

Automatic switches

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14
Q

How are automatic switches classified?

A

1) what they measure
2)condition that causes them to react

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15
Q

What type of switch is a thermostat?

A

open or rise automatic switch

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16
Q

What would a cooling thermostat be classified as?

A

a close on rise switch

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17
Q

How does a close on rise switch work?

A

as the temp rises - thermal element expands / closes its contacts to bring on the cooling system

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18
Q

What is an aquastat?

A

a switch that does for water what thermostat does for air

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19
Q

What is a thermowell?

A

It is a well that is inserted into an opening in the piping system

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20
Q

What does differential mean for switches?

A

They have variance between their open and closed positions

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21
Q

What is the fixed differential of an Aquastat?

A

15F (8.33C)

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22
Q

What is the differential pre-set of a pressure switch?

A

20 psi

23
Q

A flow switch is what type?

A

a single pole, double throw switch

24
Q

How does a flow switch operate?

A

When there is flow the paddle moves = causes pole to be pushed from one throw and pulled to another throw

25
Q

Where is a pressure switch used?

A

on mid and high efficiency gas equipment

26
Q

How does a pressure switch operate?

A

contacts close when the correct pressure is sensed.

27
Q

When replacing a pressure switch, you should use one that has the same what?

A

pressure setting

28
Q

What are float switches used for?

A

To monitor the level of liquids in a vessel

29
Q

A float switch will open or close to control what?

A

a pump supplying water to a cooling tower sump, or to shut off the burner in a steam of hot water boiler whose water level has dropped to an unacceptable point.

30
Q

What is another name for a float switch?

A

Low water cutoff

31
Q

What is this?

A

Float switch

32
Q

Where are End switches used?

A

used if the position of a piece of mechanical equipment has to be proven before the next step in a sequence of operation can take place.

33
Q

What prevents Dead - heading?

A

A zone valve that has to be proven to be open before the pump tried to move water through it

34
Q

What does a 4 wire zone valve have?

A

end switch wired across 2 of the wires which typically have red insulation

35
Q

What else is an End switch used for?

A

operations of the dampers on the inlet to a direct-fired makeup unit (DFMA)

36
Q

A dimmer switch functions as an?

A

On / off switch w/ the addition of a variable resistor built into it

37
Q

Where should a switch be located?

A

ALWAYS be located in the “hot” leg of the circuit
positioned between the source (power supply) / the load (device that turns electrical energy into work)

38
Q

What do the volts and amps have to be?

A

at least as high as those it will be exposed to

39
Q

What does a relay do?

A

allows low volts to operate high voltage equipment equipment w/o the two touching each other

40
Q

What are the 2 varieties of relays?

A

1) electromagnetic relays (EMRs)
2) solid - state relays (SSRs)

41
Q

What is the job of the 2 kinds of relays?

A

use a circuit w/ low power to operate equipment that uses a higher voltage power source.

42
Q

What is the SSR about?

A

silent in operation
has no moving parts
Wear and tear isn’t an issue

43
Q

What is EMR about?

A

has a moving armature / moving contacts
Can not be used in a volatile environment

44
Q

What is a downside of a SSR

A

limited to operating one circuit only

45
Q

Can EMRs operate multiple sets of contacts?

A

Yes

46
Q

Where are SSRs found?

A

on furnaces / boiler modules, solid state fuse / relay panels in vehicles.

47
Q

Most relays that are used in hydronic systems will be of what type?

A

EMR

48
Q

Most relays that are used in hydronic systems are of what type?

A

EMR

49
Q

What do relays consist of?

A

a Coil = temporary electromagnet
A single or multiple sets of spring loaded electrical contacts

50
Q

When a relay coil is energized and de-energized what can be heard?

A

an audible click

51
Q

What voltage values are relays capable of?

A

600V

52
Q

In a nutshell, how does a relay work?

A

It’s a magnetic switch = uses electromagnetism as the force that operates the switching mechanism

53
Q

What does SSR stand for?

A

Solid state relays

54
Q

What does EMR stand for?

A

Electromagnetic relays

Plumbing Level 3 (26 decks)

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