Figure 1-20. - Airflow diagram.

(3) which, if it sights no flame, reacts to cause a switching action that results in shutting down the burner.

FLAME FAILURE AND OPERATIONAL CONTROLS

Frequently on fully automatic boilers, you will find an electronic type of device provided for the control of flame failure. The device provides automatic start and operation of the main burner equipment. Some controls are designed to close all fuel valves, shut down the burner equipment within 4 seconds after a flame failure. and actuate an alarm. Some controls also create a safety shutdown within 4 seconds after de-energization of ignition equipment when the main burner flame is not properly established or fails during the normal starting sequence. These controls must create a safety shutdown when the pilot flame is not established and confirmed within 7 seconds after lighting. A safety shutdown requires manual reset before operation can be resumed and prevents recycling of the burner equipment.

Q16. What is the process of maintaining a difference of pressure between two points in a system called?

Q17. The flow of the air-fuel mixture supplied to the furnace is regulated by steam demand. What is this process called?

Q18. The rate at which combustion air is delivered to the blower can be changed by throttling what device?

Q19. Once a safety shutdown of a boiler has occurred, what action must be taken before operations can resume?

INSTRUMENTS AND METERS

Learning Objective: Identify the instruments and meters used on boilers and describe the function of each.

A pressure gauge is essential for safe operation of a boiler plant. However, the use of additional instruments.