Dampers, Louvers, & Diverters

This is a basic device found on most heaters and furnaces. The stack damper is necessary to adjust the draft in a natural draft furnace. Even if the designer could calculate accurately enough to exactly predict the draft in the furnace, he would still over design the stack to take care of future modifications. This damper is normally not of a tight seal type, in fact it generally is manufactured with two or three inches of clearance around the perimeter. This damper would not normally be used to control combustion air, but rather to assure that too much draft is not available in the furnace. Too much draft would result in air leakages into the furnace which would result in reduced efficiency. Manual operation is normally used, but actuators can be used for automated operations.

Butterfly dampers are single blade, low leakage or minimum leakage dampers utilizing a round, square or rectangular blade. Butterfly dampers are well suited for on/off service or flow control balancing. Electric, pneumatic, hydraulic and manual gear actuators with pneumatic or electrical positioners can be used.

The parallel design is used primarily for isolation. The use of blade edge and jamb seals achieves minimal leakage past the closed damper. These dampers are used mostly in air preheat and heat recovery systems. They would be used where a tight shut off is required, such as isolating one unit from another in a multiple unit system. Electric, pneumatic, hydraulic and manual gear actuators with pneumatic or electrical positioners can be used.

The opposed design exhibits the best flow control characteristics with moderate leakage past the closed damper. This type damper would be necessary if the accuracy of the flow amount is required or if the flow pattern must be maintained, such as when entering a burner zone. Electric, pneumatic, hydraulic and manual gear actuators with pneumatic or electrical positioners can be used.

The double louver design utilizes two banks of blades. Zero flue gas leakage is achieved by pressuring the area between two closed banks of blades with seal air. The parallel/opposed configuration provides zero leakage yet retains good flow control characteristics. These dampers can be found in applications where fast bypass capability is required during an upset condition. Double louvers can also be found where overhead space is not available to install a slide gate damper.

Slide gate isolation dampers are available in low leakage and zero leakage designs utilizing either machine screws or chain drives. Slide gate dampers can be furnished with electrical actuators, air actuators or hydraulic actuators.

Flow diverter dampers are utilized on many process and heat recovery systems to direct the flow in one or two directions. In a heat recovery system, the diverter damper would normally direct the gas to a waste heat recovery system or in a bypass mode through a silencer and stack. The diverter damper can also be furnished with a single end pivoted blade to direct the gas flow into one of the two outlets. The metallurgy of the damper is based on the design temperature and pressure of the system.