Book 1 Chapter 7: Low Water Fuel Cut-offs And Feedwater Controls

Question 1

The _______ operated low water fuel cut-off uses buoyancy to operate the switch.
A) float
B) electrode
C) bi-metal
D) thermal

Answer 1

A) float

Question 2

The type of low water fuel cut-off that uses the conductivity of the water to operate it is the __________ type.
A) float
B) thermal
C) three wire
D) electrode probe

Answer 2

D) electrode probe

Question 3

The main cause of heating boiler failure is overheating of the heating surfaces due to:
A) high water level
B) too high a steam pressure
C) low water level
D) operator error

Answer 3

C) low water level

Question 4

A low water fuel cut-off combination pump will _____ if the water level reaches a low level, but still above the lowest permissible level.
A) shut down the boiler
B) start the feewwater pump
C) close the fuel valve
D) open the safety valve

Answer 4

B) start the feedwater pump

Question 5

Low water levels can develop in hot water boilers due to human error.
A) true
B) false

Answer 5

A) true

Question 6

On a steam boiler, test the low water fuel cut-off while the boiler is operating by:
A) increasing the steam pressure
B) blowing down the boiler
C) opening the drain valve on the float chamber
D) doing a “pop” test

Answer 6

C) opening the drain valve on the float chamber

Question 7

A three wire (double pole) switch on a LWFCO will shut off the fuel and sound an alarm.
A) true
B) false

Answer 7

A) true

Question 8

At normal boiler steaming rates, a condensate receiver tank should have enough water supply to keep the boiler supplied for ________ minutes.
A) 30
B) 15
C) 45
D) 60

Answer 8

A) 30

Question 9

A leak in a condensate return pipe can cause:
A) Less fuel to be burned
B) A decrease in system water use
C) Less corrosion in the condensate system
D) A low boiler water condition
E) Less chemicals to be required

Answer 9

D) A low boiler water condition

Question 10

Equalizing lines on a condensate receiver float chamber:
A) Maintain make-up flow equal to condensate flow
B) Eliminate the need for a make-up level control valve
C) Keep receiver level equal to boiler level
D) Will dampen level fluctuations
E) Maintains equal flow of condensate to multiple boilers

Answer 10

D) Will dampen level fluctuations

Question 11

A hot water boiler low water fuel-cutoff:
A) Should be located on the expansion tank
B) Cannot be tested during routine boiler operation
C) Should be tested weekly during routine boiler operation
D) Cannot be tested
E) Must have a normally closed switch

Answer 11

B) Cannot be tested during routine boiler operation

Question 12

The low water fuel cut-off may be tested by:
A) Opening the gauge glass drain
B) Decreasing the firing rate
C) Adjusting the level controller to maximum
D) Closing the feedwater inlet valve and opening the blowdown valves
E) Opening the feedwater inlet valve closing the blowdown valves

Answer 12

D) Closing the feedwater inlet valve and opening the blown down valves

Question 13

Low hot water heating boiler water level can be caused by:
A) Feedwater flow exceeding steam flow
B) Excessive blowdown (blowoff)
C) Swell in the boiler
D) High boiler conductivity
E) Low phosphate leve

Answer 13

B) Excessive blowdown (blowoff)

Question 14

When a boiler equipped with a combination feedwater control and low water cutoff device shuts down due to a low water condition:
A) Level must be restored to above the cut-off line before the unit can be restarted
B) A manual reset switch on the boiler control panel must be used
C) A prepurge of the boiler before it is restarted will not be necessary
D) The feedwater flow to the condensate receiver tank will also stop
E) It can be restarted by simply resetting the low water fuel cut-off switch

Answer 14

A) Level must be restored to above the cut-off line before the unit can be restarted

Question 15

On LP steam heating boilers, the low water fuel cut-off should operate when:
A) There is excessive blowdown or leakage
B) The boiler water level drops below 25mm (1in) in the gauge glass
C) The float chamber drain is opened
D) The boiler feedwater flow is stopped during operation
E) All of the above

Answer 15

E) All of the above

Question 16

There are many different types of low water fuel cut-off devices used on boilers. The low water fuel cut-off will operate if the:
A) Float drops down in the float chamber
B) All of these answers
C) Mercury switch is tilted
D) Water uncovers both probes
E) Water level in the boiler is not adequate

Answer 16

B) All of these answers

Question 17

The low water fuel cut-off must;
A) Be repaired immediately on detection of failure
B) All of these answers
C) Not have isolation valves installed
D) Not be electronically disabled
E) Not be physically disabled

Answer 17

C) Not have isolation valves installed

Question 18

Relief valve discharge due to overfiring a hot water boiler can cause:
A) High level of solids in boiler water high level in the expansion tank
B) High level in the expansion tank
C) Low system water temperature
D) Low boiler water level
E) Backflow to city domestic water

Answer 18

D) Low boiler water level

Question 19

Feedwater pump failure:
A) Causes the level in the hotwell to drop
B) Increases the load on the deaerator
C) Causes a low water condition in the boiler
D) Causes the feedwater temperature to rise
E) Causes the feedwater supply pressure to increase

Answer 19

C) Causes a low water condition in the boiler

Question 20

The CSA code B51-09, Part 6.3.2.2 states that automatically fired hot water boilers not under continuous attendance by a certified operator must be equipped with a low water fuel cut-off switch which:
A) May be equipped with isolation valves to isolate it from service
B) Cannot be rendered inoperative or tampered with
C) Can also activate an alarm
D) Must be a normally open switch
E) Must be a manually reset device

Answer 20

B) Cannot be rendered inoperative or tampered with

Question 21

In nearly all LP steam heating systems the feedwater:
A) Is a high make-up percentage
B) Requires daily close scrutiny of chemical values
C) Is usually condensate
D) Requires preheating in an economizer
E) Must be deaerated

Answer 21

C) Is usually condensate

Question 22

Overheating of boiler heating surfaces due to low water:
A) Can be prevented with proper water treatment
B) Can be eliminated with a low water fuel cut-off
C) Is the main cause of boiler failure
D) Cannot occur if the boiler is a hot water unit
E) Will cause a furnace explosion

Answer 22

C) Is the main cause of boiler failure

Question 23

The low water fuel cut-off on steam boilers will operate if:
A) The low side connection valve is closed
B) The high side connection valve is closed
C) The feedwater regulator fails open
D) The drain valve is closed
E) The float chamber drain valve is opened

Answer 23

E) The float chamber drain valve is opened

Question 24

A mercury switch in a float operated Low water fuel cut-off consists of:
A) Diaphragm strainer and bellows assembly
B) A float and rod
C) Electrode and transformer
D) Motorized valve
E) Glass bulb, electrical contacts, small amount of mercury

Answer 24

E) Glass bulb, electrical contacts, small amount of mercury

Question 25

During monthly testing of Low Water Fuel Cut-off devices, the burner should shut down when the visible level in the gauge glass is approximately:
A) 75mm (3in)
B) 2 inches below the bottom of the gauge glass
C) Half way in the glass
D) 2.54cm (1in) above the bottom of the gauge glass
E) Any time the level is below normal

Answer 25

D) 2.54cm (1in) above the bottom of the gauge glass

Question 26

The low water fuel cut-off float is commonly used to operate both the Low water fuel cut-off switch and the:
A) Feedwater control switch
B) High steam pressure switch
C) Low feedwater temperature alarm
D) Low steam pressure alarm
E) Low fuel gas pressure switch

Answer 26

A). Feedwater control switch

Question 27

A second source of feedwater may be controlled by the:
A) Boiler operating control
B) Feedwater control switch
C) Boiler drum level control
D) Low water fuel cut-off device
E) Automatic blowdown device

Answer 27

D) Low water fuel cut-off device

Question 28

Possible causes of low water level include:
1. Leaks caused by breakage or corrosion
2. Excessive blowdown
3. Automatic feedwater valve passing
4. Boiler feed pump failure
5. Excessive make-up

A) 2,3,5
B) 1,2,4
C) 2,3,4
D) 1,2,3
E) 3,4,5

Answer 28

B) 1,2,4

Question 29

Make-up water for the heating system usually comes from the:
A) Deaerator
B) Returning condensate
C) City water supply
D) Boiler feedwater
E) Boiler feedwater pump

Answer 29

C) City water supply

Question 30

The float in the low water fuel cut-off will activate:
A) An electrical relay
B) An electrical switch
C) A gate valve
D) A solenoid valve
E) A globe valve

Answer 30

B) An electrical switch

Question 31

Low water fuel cut-off devices require regular attention, the following intervals are recommended:
1. Once per shift
2. Daily
3. Weekly
4. Monthly
5. No attention is required

A) 2,3,4
B) 3,4,5
C) 1,2,3
D) 2,3,5
E) 1,2,4

Answer 31

A) 2,3,4

Question 32

In a building heating system the condensate in the condensate receiver tank comes from the:
A) Make-up water supply
B) Boiler feedwater
C) Heating system
D) Economizer
E) Deaerator

Answer 32

C) Heating system

Question 33

The float operated low water fuel cut-off works on the principle of:
A) Differential pressure
B) Drum level variation
C) Temperature change
D) Buoyancy
E) Steam density

Answer 33

D) Buoyancy

Question 34

The main cause of heating boiler failure is overheating of the heating surfaces due to:
A) High firing rates
B) Low steam conditions
C) Scale build-up
D) High water conditions
E) Low water conditions

Answer 34

E) Low water conditions

Question 35

At normal boiler steaming rates, a condensate receiver tank should contain a sufficient volume of water equivalent to the water evaporated by the boiler for a maximum period of _____ minutes.
A) 45
B) 20
C) 60
D) 15
E) 30

Answer 35

E) 30