Model PRD & PRD- RD
TB-224
P/N 090375A0224 REV. M
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EWC Controls Inc. 385 Highway 33 Englishtown, NJ 07726 800-446-3110 FAX 732-446-5362 E-Mail- info@ewccontrols.com
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Barometric By-Pass Damper
GENERAL DESCRIPTION
Note: This drawing of the Bypass damper, Hand Damper, Static Pressure control and Related duct work is intended to serve only as a guide.
Your actual duct work layout and components may differ. Use the graphic as a guide when planning or designing a Zone system regardless of
the Equipment type, Duct layout and Airflow configuration.
Supply Air
to
Zone Dampers
Pitot Tube
Ultra-Zone
™
PS4
Static Pressure Control
EBD
Motor Actuated or Barometric
PRD or PRD - RD
ByPass Damper
3/8” O.D.
Reference Tubing
Ultra-Zone
™
Ultra-Zone
™
HVAC
UNIT
Return Air
from
All Zones
Ultra-Zone
™
Zone Control
Panel
24vac Power
Control Wiring
Supply
Air
Sensor
(required)
RD-HD
SID-HD
ND-HD
Hand
Damper
Return
Air
Sensor
(optional)
M
P
Ultra-Zone
™
6ft. if possible
6ft. if possible
-
The model PRD & PRD-RD pressure regulating dampers are a single blade rectangular or round barometric damper
assemblies with a counter balanced weighted arm. The barometric by-pass damper is an economical way to manage
airflow when zone dampers close. Damper adjustment is achieved by off-setting the hex shaped arm, securing
weight #1 towards the bottom of that arm and moving the extra weight(s) (optional) up or down the arm, until the
correct bypass flow is achieved. See Page 2 for details. For field versatility, the hex shaped arm can be inserted into
either side of the damper. Additional weights can be added if necessary.
The barometric by-pass damper is installed in the duct-work to regulate excess air pressure and volume. The damper
can be mounted to relieve pressure by returning the air back to the return air duct or by dumping it into a non-critical
conditioned area.
A restricting hand damper can be installed downstream of the by-pass damper, which allows the
installer to set sufficient differential pressure across the bypass duct, controlling how fast the by-pass air mixes with
return air. See Application Note 090376A0169D.
The PRD & PRD-RD are effective By-Pass solutions for any Constant Speed or Variable Speed Zoned HVAC system
up to 4 ton capacity.
MODEL #
SIZE
BYPASS Cfm*
560 Cfm
700 Cfm
825 Cfm
900 Cfm
1125 Cfm
1375 Cfm
12" x 8"
12" x 10"
12" x 12"
20" x 8"
20" x 10"
20" x 12"
PRD 12 x 8
PRD 12 x 10
PRD 12 x 12
PRD 20 x 8
PRD 20 x 10
PRD 20 x 12
# WEIGHTS
2
2
2
2
2
2
* CFM @ 900Fpm
(.15”wc friction loss)
BYPASS Cfm*
850 Cfm
1100 Cfm
1300 Cfm
1300 Cfm
1750 Cfm
2000 Cfm
* CFM @ 1400Fpm
(.3”wc friction loss)
MODEL #
BYPASS Cfm*
320 Cfm
500 Cfm
720 Cfm
950 Cfm
1250 Cfm
8"
10"
12"
14”
16"
PRD-RD 8
PRD-RD 10
PRD-RD 12
PRD-RD 14
PRD-RD 16
# WEIGHTS
1
1
1
2
2
BYPASS Cfm*
500 Cfm
750 Cfm
1100 Cfm
1400 Cfm
1900 Cfm
Use the Cfm tables provided below to size your by-pass damper using the guideline provided on the next page. Use
the 1400Fpm column to achieve smaller bypass runs at higher velocities. Use the 900Fpm column if you have the
space to accommodate a large bypass run at a nominal velocity.
SIZE
* CFM @ 1400Fpm
(.3”wc friction loss)
* CFM @ 900Fpm
(.15”wc friction loss)
