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6
Furnace
Plenum
Connecting
Duct
Counter-
weighted Arm
Cold Air
Return
Air pressure
bypass damper
closed; all zones
open and/or
not operating
Partially open; one
or more zones closed;
fan operating
Open position;
most zones closed;
fan operating
133-0010
ZONE-AIR
BYPASS DAMPER
INSTALLATION INSTRUCTIONS
DESCRIPTION
This bypass damper was designed for use with zoned
warm air heating and air conditioning systems. It is
installed in a connecting duct between the furnace ple-
num or the supply duct and the cold air return duct.
Its purpose is to control and compensate for excess
volume and velocity of the air due to the closing of the
dampers leading to some of the zones.
The bypass damper, operating by means of air pressure,
permits any excess volume of air to pass directly to the
cold air return, avoiding an increased air velocity through
the remaining open ducts which would result in discomfort
to the occupants of that zone.
INSTALLATION
All parts needed for the bypass damper are provided
except the damper vane. The vane should be cut from a
piece of sheet metal to the proper size to fit the duct.
The bypass duct should be properly sized. It should be
designed to handle at least the same amount of air as the
supply duct, less that required by the smallest zone.
The damper located in the bypass duct has a counter-
weighted arm. It operates through the pressure of the air
as opposed to the torque of the weighted arm. Adjust the
counterweight so that with all zones calling for heat, the
fan in operation, and all ducts open, the bypass damper
is in the closed position.
If several zones are not calling for heat, the bypass
damper should be partially open; if only one zone is calling
for heat, the bypass damper should be open.
See the layout for zoned warm air system on page 2 for
additional information.
NOTE