Chapter 87

Question 0

A boiler control manual - automatic transfer or selector station:
A) can be used to manually override automatic control loops
B) can be changed from manual to automatic without balancing
C) is located upstream of the controller in a control loop
D) output is directed to the primary element of a loop
E) must be operated in manual mode for only short periods

Answer 0

A) can be used to manually override automatic control loops

Question 1

Low water fuel cutoff must shut the fuel off before the water level drops to:
A) the lowest possible water level
B) the fire line
C) the lowest visible water level in the gauge glass
D) 25 mm above the bottom of the gauge glass
E) the lowest heating surface

Answer 1

C) the lowest visible water level in the gauge glass

Question 2

Modulating combustion control will:
A) change air and fuel flow proportionally to steam pressure change
B) always be at set point when demand is at 50%
C) alter only the air flow if a transfer station is in manual
D) respond to changes in atmospheric pressure
E) always be a cascading control system

Answer 2

A) change air and fuel flow proportionally to steam pressure change

Question 3

Modulating combustion control on a heating boiler is accomplished by changing the amount of _____ and ____ to the burner.

Answer 3

Fuel, air

Question 4

State the purpose of the low water cutoff device.

Answer 4

The LWCO shuts the fuel off to the boiler if the water level in the boiler falls below the lowest safe water level

Question 5

According to the ASME code, explain the requirements for high pressure limit switches.

Answer 5

The code states that all automatically fired steam boilers must have a high limit pressure activated switch that shuts off the fuel to the burner when the steam pressure exceeds normal operating pressure.

Question 6

Describe modulating combustion control as it applies to a steam boiler.

Answer 6

Modulating control occurs when the burner remains lit at all times but the flame size is increased and reduced by controlling fuel and air flow to the burner according to steam pressure. As the steam pressure drops, the fuel flow and air are increased, and vice versa.