EWC Controls PRD Technical Bulletin

GENERAL DESCRIPTION

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.
Return Air
from
All Zones
Ultra-Zone
™
RD-HD
SID-HD
ND-HD
Hand
Damper
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.
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.
MODEL # # WEIGHTS
SIZE
PRD 12 x 8
12" x 8"
PRD 12 x 10
12" x 10"
PRD 12 x 12
12" x 12"
PRD 20 x 8 20" x 8"
PRD 20 x 10 20" x 10"
PRD 20 x 12 20" x 12"
TB-224
EWC Controls Inc. 385 Highway 33 Englishtown, NJ 07726 800-446-3110 FAX 732-446-5362
P/N 090375A0224 REV. M
6ft. if possible
Return
Air
Sensor
(optional)
Ultra-Zone™
Zone Control
BYPASS Cfm*
BYPASS Cfm*
560 Cfm 850 Cfm
2
2 700 Cfm
1100 Cfm
2 825 Cfm
1300 Cfm
2 900 Cfm
1300 Cfm
1125 Cfm
2 1750 Cfm
1375 Cfm
2000 Cfm
2
* CFM @ 900Fpm
* CFM @ 1400Fpm
(.15"wc friction loss)
(.3"wc friction loss)
©
Copyright 2006-2008 EWC Controls All Rights Reserved
Barometric By-Pass Damper
Leave this bulletin on the job site for future reference!
6ft. if possible
HVAC
UNIT
Supply
Air
Sensor
(required)
Panel 24vac Power
Control Wiring
MODEL #
SIZE
PRD-RD 8 8"
PRD-RD 10
10"
PRD-RD 12 12"
14"
PRD-RD 14
PRD-RD 16 16"
Model PRD & PRD- RD
Zone Dampers
Ultra-Zone
Pitot Tube
M P
Reference Tubing
Ultra-Zone™
Static Pressure Control
Ultra-Zone ™
EBD
Motor Actuated or Barometric
PRD or PRD - RD
ByPass Damper
# WEIGHTS
BYPASS Cfm*
320 Cfm
1
500 Cfm
1
1
720 Cfm
2 950 Cfm
1250 Cfm
2
* CFM @ 900Fpm
(.15"wc friction loss)
E-Mail- info@ewccontrols.com
Supply Air
to
™
3/8" O.D.
PS4
-
BYPASS Cfm*
500 Cfm
750 Cfm
1100 Cfm
1400 Cfm
1900 Cfm
* CFM @ 1400Fpm
(.3"wc friction loss)
1