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and
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Engineering
Guide
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Reference
70-6925 61
RP973 Pneumatic Averaging Relay
A three-port relay used in HVAC systems averages the signals
from two thermostats to control a single device such as a heating
coil valve for a multizone unit. The pneumatic averaging relay
provides an output pressure equal to the average of two input
pressures. Replacement devices are available for Johnson,
Powers, Robertshaw, Barber-Colman, and older Honeywell
devices.
• In-line, wall or panel mounted.
• Sharp-barb air connections.
• Molded plastic construction.
RP973A Typical Piping Typical Averaging Application
Type: Pneumatic Three-Port Averaging Relay
Dimensions, Approximate: 1 1/2 in. high x 7/8 in. wide x 15/16 in.
deep (38 mm high x 22 mm wide x 24 mm deep)
Airflow Usage: 0.007 scfm (3.303 mL/s) maximum
Air Connections: Barb fittings 5/32 in. (4 mm) O.D. plastic tubing
Capacity: 0.039 scfm at 1 psi differential (18 mL/s at 5 kPa differential)
Operation: Output pressure equals average of two input pressures
Mounting: Wall or In-line or panel
Operating Humidity Range (% RH): 5 to 95% RH
Temperature Range: 32 F to 125 F (0 C to 52 C)
Maximum Safe Operating Pressure: 30 psi (205 kPa)
Output Operating Pressure: 3 to 15 psi (21 to 103 kPa)
M
.007 IN.
RESTRICTOR
.005 IN.
BLEED-TYPE
THERMOSTAT
EXH
5
5
2
2
3
3
INPUT 1
INPUT 2
RP973A
RP470B LOCKOUT
RELAY PIPED AS
A REPEATER
TO CONTROLLER
RP470B RELAY ALLOWS THE USE OF AN AVERAGING
RELAY ON SMALL-NOZZEL BLEED DEVICES.
1
1
C4475
.007 IN.
RESTRICTOR
M
2
35
TO
CONTROLLER INPUT
RP973A
LP914
SENSOR 1
LP914
SENSOR 2
INPUT 1 + INPUT 2
2
OUTPUT =
C4476
1
1
RESTRICTOR
Product Number Operation
Input Operating Pressure Output Operating Pressure
Description(psi) (kPa) (psi) (kPa)
RP973A1005 Output pressure equals
average of two input
pressures
3 to 15 psi 21 to 103 kPa 3 to 15 psi 21 to 103 kPa Output is the average of the two inputs.
Pneumatic Three-Port Averaging Relay.
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