How a Flame Safeguard Works

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How a Flame Safeguard Works

A flame safeguard system is crucial to the operation of any modern boiler. Once you understand how they work, it’s easy to see how important they are to safety and efficiency. In fact, a flame safeguard is an active part of a boiler’s operation from startup to shutdown, starting with the moment there is demand on the boiler.

Start Off Sequences

When a burner is started up, a sequence of events has to happen in the correct order to make sure the burner starts properly, and stays lit. The flame safeguard makes sure everything goes smoothly. The flame safeguard’s main functions are to monitor the presence of flame in the burner, and to ensure that everything proceeds according to plan for light-off. This includes commanding damper motors to important positions at critical phases in the sequence. 

Damper Control

It’s crucial to ensure that the combustion chamber is fully purged prior to light-off, so the damper is generally driven to the open position. Prior to light-off, the damper is opened fully to ensure 4-5 full air exchanges. The damper is then driven closed to improve light-off reliability. Once the burner is lit, the flame-safeguard allows a firing rate control to regulate the damper and corresponding fuel according to system demand.

On shutdown, whether it’s a planned shutdown, flame interruption, or another circumstance, when the flame is no longer detected, the flame safeguard will initiate the burner’s “post-purge”. This allows the continued flow of fresh air into the combustion chamber to clear away unused fuel or combustion byproducts and send them out the stack.

How It Works

The flame safeguard doesn’t actually power the modulating motor. Instead, the flame safeguard closes contact sets that feed from and to the mod motor to direct it to the purge, light-off, and modulation modes. For flexibility, the “dry” contacts can control a variety of devices from a simple mod motor to inputs on a more complex PLC system. During testing and maintenance, these wires can be jumpered at the sub-base to verify either the mod motor operation or inputs on more complex systems.

If you need help with a flame safeguard system, or with any part of your boiler, if you need service or maintenance, or if you’re looking for a new boiler system, the experts at WARE are standing by to help. Please contact us at your convenience.

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