-Dan Wallace, PE
1. Make sure tubing is pitched downward to avoid condensation in the impulse lines. Liquid in the impulse lines can cause incorrect draft measurements and have adverse effects on fired equipment operation.
2. If the draft pressure sensor is located below the sensing point, ensure there is an adequate drip leg to collect condensation.
3. The size and shape of the sensing line impacts the draft control response. One may need to adjust the filter parameter in the draft controller to get better draft readings.
4. Especially with low NOx burners, it often advantageous to place draft control in manual to ensure poor draft control (poor PID settings, installation, etc..) is not affecting combustion. Varying draft pressure upstream of the draft damper can cause large variations in FGR flow that can upset burner stability and performance.
5. It is advisable to use an opposed blade draft damper instead of a single blade damper in many applications.
6. Burners that use FGR often require a positive pressure upstream of the draft damper. However, there are older brick-set boilers that require a negative furnace pressure so be careful when selecting a draft pressure setting. Consult boiler and burner manuals for correct settings.
Dan Wallace, PE is the Vice President of Research and Development at Preferred Utilities Manufacturing Corporation in Danbury, CT, and has been with the company for over 10 years.