CAB Maintenance Tips

Combustion System Maintenance for CAB Brazing Furnace Systems

Cross-connected air/gas regulator system
The cross connected regulator system is the most common system for keeping air and gas in the proper ratio at all firing rates.  The regulator is the heart of the system.  An air impulse line carries air pressure to the upstream side of the regulator diaphragm and gas pressure to the downstream side.  If the two pressures are not equal, the diaphragm will move to open or close the regulator and bring them into balance. 

To check the ratio regulator, hook a manometer to the air line and the downstream gas line. If the pressures are equal, the manometer will read zero. As the air pressure changes and the control valve moves, the gas pressure will lag behind the air pressure by about one half inch W.C.   Violent swings of an inch or two or erratic movements indicate regulator problems or a plugged impulse line.

Dirt and trash in the piping
Dirt and trash in the piping is a common problem in combustion systems. Air going into the blower must be clean.  A drop in air pressure will indicate a plugged intake screen or combustion air filter and will decrease furnace performance.

Pilots are particularly sensitive to dirt due to the small passages involved.  In some cases, it may be necessary to install a pilot line air filter or a solenoid valve in the pilot line to shut off the flow of air through the line when the pilots are off to help slow the accumulation of dirt.

It is important to assure the gas supply is clean.  A "Y" type strainer may be installed in your gas supply line to assure the lines remain clean.

Blower Pulsation
Blower pulsation at low fire can wreak havoc on pilot flames.  The pulsation causes a change in the air fuel ratio that can quench the pilot.  Pulsation can be minimized  by venting the blower at low fire or by installing a pressure regulator in the pilot air line.

Deterioration of components
After a period of service, combustion problems may occur due to deterioration of burner castings, burner tiles, or burner flame shielding tubes. The only way to detect this type of deterioration is to carefully inspect the components on a periodic basis.  

Reprinted from Heat Treating Furnace Seminar presentation on maintenance and installation, edited for cab brazing by Chuck Field, Project Engineer.  

The latest design, materials and equipment specifications should be obtained from the company before any reliance is placed on the enclosed since changes may occur due to product improvement.