Static Pressure Controlled Bypass (MODULATING)
Air Probe (Pitot Tube)
DO NOT allow
supply air
pressure to blow
directly into the
pitot tube
PITOT
TUBE
To test if bypass is sized and
configured properly, make a call ONLY
from the smallest zone for cooling with
the fan at the HIGHEST speed and the
BYPASS Damper should fully or almost
fully open within 1 to 2 minutes
Just as soon as the motor starts to
run open, turn the knob back
clockwise just enough that the
damper motor stays closed.
(ECOJAY damper RED light will be
solid)
ecojay
P
O
P
C
C
O
M
ecojay
P
O
P
C
C
O
M
4
AIRFLOW
Locate the air probe (pitot
tube) at least
2 FEET
downstream from the air
source, preferably as close
to the center of the
airstream as possible
2 -2.5
10"
3 -3.5
12"
4 -4.5
14"
5
14 -16"
Unit Size
Round Damper
(Tons)
Size (Inches)**
BYPASS DAMPER “RULE OF THUMB”
Below chart assumes 400 CFM per Ton
**USE next size UP round bypass damper for any
system with a single zone less than 200 CFM.
BYPASS DAMPER (Pressure Relief)
A bypass system
consists of a short duct connecting the supply plenum to the return
air plenum.
A “bypass” damper is installed in this duct that opens
/
closes automatically to maintain constant pressure inside the duct
when zones open and close. When the correct size bypass damper
is installed and adjusted correctly, it will be fully CLOSED when all
zones are calling (no air bypassing) and will OPEN proportionately
as more zone dampers close.
BYPASS DAMPER SIZING:
Select a round damper size with a Max CFM greater than the CFM-
Needed to bypass. Use the formula below to calculate CFM needed
to bypass and the ROUND DAMPER CFM CHART to check Max CFM.
T
YPICALLY
400
CFM
PER
TON
U
SE
“N
ORMAL
CFM”
FROM
THE
CFM CHART
(P
AGE
: 8)
U
SE
A
BYPASS
D
AMPER
THAT
HAS
LARGER
“M
AX
CFM”
800 = 2
1200 = 3
1600 = 4
2000 = 5
Bypass SIZE
E
QUIPMENT
A
IRFLOW
C
APACITY
IN
CFM (
HIGH
SPEED
)
CFM
OF
S
MALLEST
ZONE
CFM-N
EEDED
TO
BYPASS
EXAMPLE: 4-T
ON
EQUIPMENT
WITH
10"
SMALLEST
ZONE
:
1600 CFM
(
EQUIPMENT
)
–
400 CFM
(
SMALLEST
ZONE
–
N
ORMAL
CFM
ON
P
AGE
: 8)
= 1200 CFM N
EEDED
SO,
FROM
THE
R
OUND
D
AMPER
MAX CFM
ON
P
AGE
: 8,
A
14"
ROUND
DAMPER
SHOULD
BE
USED
FOR
BYASS.
Initial Weight-Arm Positions
depend on
AIRFLOW
and
ORIENTATION
of the bypass damper. Below are the four (4)
initial weight arm positions. Select AIRFLOW & ORIENTATION for specific application.
NOTE: Extra weight may be required for
upflow applications. (Order ABDW)
Up-Flow
4
o’clock Position
Left to Right
4
o’clock Position
Right to Left
8
o’clock Position
Down-Flow
4
o’clock Position
11