Limits & Interlocks

Question 1

What type of controller is used for a hot water boiler?

Answer 1

Temperature control - operator aquatstat

Question 2

What is limit control actuated by? (3)

Answer 2

1. Temperature
2. Pressure
3. Liquid level

Question 3

How are safety limits typically wired in an electrical circuit?

Answer 3

In series

Question 4

What type of control switch is the best example of a running interlock?

Answer 4

combustion air switch

Question 5

Describe what a recycling interlock is?

Answer 5

When broken, the cycle resets and allows the flame safeguard control to recycle once conditions return to normal

Question 6

Describe what a running interlock is?

Answer 6

Can be opened at the beginning of start up cycle but must be
closed prior to the pre-purge cycle, and remain closed throughout the burner’s ignition and
run cycle.

Question 7

Describe what a non-recycling interlock is?

Answer 7

An Interlock which, when broken during the burner’s running cycle, does not reset and allow
the flame safeguard control to recycle once conditions return to normal

Question 8

Describe what a pre-ignition interlock is.

Answer 8

An Interlock that must be made prior to the burner’s ignition cycle, and once the burner is
successfully started the interlocks can be opened/bypassed

Question 9

A flue gas spill switch does not require manual reset. True or False?

Answer 9

False

Question 10

What is the purpose of the end switch in a flue vent damper?

Answer 10

Proves the damper is open and allows normal start-up of the burner

Question 11

What is the purpose of an appliance draft inducer air proving switch?

Answer 11

Proves the fan is running and allows normal start-up of the burner

Question 12

Where is a low gas pressure switch located on a fuel train?

Answer 12

Upstream of the two safety shutoff valves

Question 13

______ controls can be either high or low limit type and are normally set beyond the normal operating range of the heating unit or appliance

Answer 13

Limit

Question 14

Limits are normally wired in series. True or False?

Answer 14

True

Question 15

Insure a safe burner start up and run
sequence by interlocking the various
burner equipment functions with the
_______ __________ control system

Answer 15

flame safeguard

Question 16

________ provide additional
safety and reliability to the operating of the heating unit

Answer 16

interlocks

Question 17

A burner motor with an air switch is an example of an _______ in series with the flame safeguard control system

Answer 17

interlock

Question 18

what is a pressuretrol?

Answer 18

Steam pressure switch that cuts out burner once satisfied - operates on a pressure differential

Question 19

Flow switches can be of the water or air type. True or False?

Answer 19

True

Question 20

_______ flow witches are generally a
proving switch proving that the pump is
operating.

Answer 20

water

Question 21

If the pump is running it will push water past the flow switch, moving the _______ and completing the circuit in the housing. Electricity is then sent to the _______ and the burner can now fire

Answer 21

paddle, burner

Question 22

High limit aquastat senses water
temperature and opens contacts if
temperature reaches _____f

Answer 22

200f

Question 23

High limit on a furnace senses air
temperature and opens contacts if air temperature reaches _____f

Answer 23

200f

Question 24

Aquastat is a normally ______ switch

Answer 24

closed

Question 25

Aquastat remains closed until water reaches a temperature around _____f

Answer 25

180f

Question 26

Once the water cools a number of
degrees (usually ___) the aqua stat contacts close the burner fires up again.

Answer 26

20

Question 27

Name the two types of aquastats

Answer 27

1. direct-mounted aqaustat with horizontal probe
2. remote bulb aquastat

Question 28

Where are spill switches located?

Answer 28

Entrance to the draft hood

Question 29

What is the purpose of a spill switch?

Answer 29

To detect flue gases that may spill from the draft vent or hood

Question 30

Most flue gas spill switches must be
reset manually although some are
automatic reset. True or False

Answer 30

True

Question 31

End switches are ______ switches. Proves that another piece of equipment has done its job.

Answer 31

proving

Question 32

Name two examples where you may find an end switch?

Answer 32

Zone valve on a boiler

Vent damper on a furnace

Both instances won’t allow the boiler/furnace to operate

Question 33

Gas pressure controls should be set at __% above the highest measured pressure under flow

Answer 33

25%

Question 34

B149.3 says to not more than 125% of the normal operating pressure at the maximum firing rate (This doesn’t work when the control is installed before the ______ rate valve

Answer 34

firing

Question 35

Gas pressure switches can be used for? (3) and are usually _______ reset

Answer 35

Gas
Air
Propane

manual reset

Question 36

Gas pressure switches can also be used for proving __________ air and are automatic reset

Answer 36

combustion

Question 37

_________ are conditions that need
to be satisfied before you start the
appliance.

Answer 37

Permissives

Question 38

Example of permissives are (4)

Answer 38

1. Thermostats
2. Aquastats
3. DDC contacts
4. timer

Question 39

Permissive switches are wired in ______ and will open the entire circuit if one condition is not met

Answer 39

series

Question 40

An interlock can be a permissive
but a permissive cannot be an
interlock. True or False?

Answer 40

True

Question 41

Difference between a permissive and interlock?

Answer 41

Permissive need to be met before a machine starts and interlocks activate during a process that has already started

Question 42

A pump that is shut down due to a low level of liquid is a __________

Answer 42

interlock

Question 43

Low suction pressure that does not allow a compressor to start is an example of a __________

Answer 43

permissive