Boiler Controls Flashcards
What is the float operated low water fuel cut off ?
-Uses the principle of buoyancy
-Used on low pressure, cast iron heating boilers
-connects to electrical switch to solenoid
-when the boiler level drops below the minimum safe level, the float drops and opens the electrical switch contact point. This interrupts the solenoid fuel valve and closes it, stopping the supply of fuel
What is a pump controlled/ low water fuel cut-off ?
-This is used to start a feedwater pump or to open a feedwater solenoid valve to supply more water.
What are some possible causes for low water level ?
- Leak in piping or boiler caused by breakage or corrosion
- Excessive blow off
- Relief valve discharge caused by overfiring on hot water boilers, even though the automatic fill valve is operational
- boiler feed pump failure
What are the 4 distinct methods of burner operation controls ?
- On- off control
-Burner fires at constant rate that is sufficient to maintain boiler pressure or temperature at full load - High-Low control
-2 firing rates are available. Rate used depends on boiler load. More efficient than On- off controls. Less of a pressure fluctuation - Modulating controls
-The firing rate is continuously adjusted to match a varying boiler load. Operation is the most efficient - High Limit controls (high steam pressure or temperature fuel cut-off)
-this control is used to shut down the fuel supply in an event of to high steam pressure or water temperature. Helps prevent possible explosion
What is a flame scanner ?
A device used to observe a flame in a boiler. If the flame is not detected the scanner will send a signal to close the fuel supply valve.
What is a thermocouple ?
a device used for flame failure detection. Senses the heat of the flame
What is the maximum allowable water temperature in a hot water boiler ?
120 C Or 248 F
What is the maximum time allowed for a gas valve to close following a flame failure on a gas burner with an electronic flame scanner ?
4 seconds
The time taken for the automatic pilot valve to close in the event of a loss of flame detection is about __________?
10 seconds
What is the name given to the component that coordinates and sequences the boiler operation?
Programing controller
What device is used to determine if the fan motor is working?
Airflow switch
Which of the following would not cause the main burner to stay on during low-fire operation mode?
a) Inoperative damper motor
b) Damper positioning switch is in the wrong position
c) The boiler pressure is below the high-low fire control setting
d) A defective high-low modulating control
c) The boiler pressure is below the high-low fire control setting
What is the duty of the hot water heating automatic fill valve ?
To maintain system pressure, regardless of level
Two conditions that may occur during warm-up of a cold boiler are smoking and ________?
Flue gas condensation
-Slight smoking
-furnace temps is not high enough yet to vaporize the incoming fuel oil immediately and completely
-Gas condensation
- caused by the water vapor in the flue gases that strikes the cold heating surfaces of the boiler and cools down below the condensation point
what are some examples of boiler items that should be tested monthly ?
- Operate the safety relief valves manually
- Test the flame detection devices
- Test the low-water fuel cut-off, if piping arrangements permit this without draining a large amount of water from the boiler
- Check the operation of the operating controls
Why must a hot water boiler be equipped with water supply and returns valves ?
So the boiler can be drained without draining the entire system
