Operating Limits - Honeywell RP972A Notice D'installation

Operating Limits:

Temperature: 0 to 140°F (-18 to 60°C)
Relative Humidity: 5 to 95%
Action: Proportional (branchline pressure decreases
with increase of pilot signal at 1:1 ratio)
Settings:
A: Output = 13 psi (90 kPa) - Pilot
B: Output (Port 2) = 16 psi (110 kPa) - Pilot (Port 3).
Factory set.
C: Output = 18 psi (124 kPa) - Pilot
Air Handling Capacity (Feed and Bleed): 0.039 scfm
at ± 1.02 psi droop (18.3 ml/sec at 7 kPa droop). Con-
ditions: 18 psi (124 kPa) Main and 9 psi (62 kPa) Pilot
Air Consumption: 0.002 scfm (1.0 ml/sec) maximum
Construction: Neoprene diaphragm, valox valve seats,
steel spring, 100 mesh stainless steel, screen main and
branch ports
Operation
When the relay is balanced, the main valve port and
exhaust valve port are closed. At balance point, the
Output force equals the algebraic sum of the spring force
plus pilot pressure force. As pilot pressure increases, the
spring compresses and the valve's exhaust port opens.
The Output flows out of the exhaust valve until a new
balance point is found and the exhaust port closes. As
pilot pressure decreases, the spring extends the exhaust
tube until a new balance point is found and the main
valve port closes.
The indicator is set on Position B for reversing 3 to 13 psi
(21 to 90 kPa) signals. In the absence of a pilot pressure,
the spring pushes the exhaust tube against the
diaphragm and allows main air into the branch line. See
Fig. 5A.
When the branchline pressure equals 16 psi (110 kPa),
the pressure on the feedback diaphragm equals the
adjustment spring pressure and the exhaust tube drops,
closing off the feed to the branch chamber and Port 2.
The relay is now in a balanced condition. See Fig. 5B.
Any air entering the pilot chamber compresses the
spring, opening the exhaust chamber port and lowering
the branchline pressure accordingly. See Fig. 5C.
As pilot pressure decreases, the spring pushes the
exhaust tube up, allowing main air to enter the branch
line and raise the branchline pressure. When branchline
pressure equals the spring pressure minus the pilot
pressure, the exhaust tube retracts and the relay is
balanced with the new, higher branchline pressure.
RP972A PNEUMATIC REVERSING RELAY
1
DIAPHRAGM 1
MAIN
BRANCH
CHAMBER
3
PILOT
1
MAIN
3
PILOT
1
MAIN
3
PILOT
Fig. 5. RP972A operation.
Application
The RP972A is used to reverse a pneumatic signal in
direct proportion to the input. Fig. 6 shows how the
RP972A controls a chilled water (CW) valve. When the
temperature increases, the Direct Acting (D.A.)
thermostat outputs an increasing branch line. This closes
the Normally Open (N.O.) hot water (HW) valve and,
through the reversing action of the RP972A, opens the
N.O. CW valve.
DIRECT
ACTING
THERMOSTAT
M B
MAIN
M
Fig. 6. Use of RP972A to control a cold water valve.
3
RP972A
FEEDBACK
DIAPHRAGM
2
BRANCH
EXHAUST
4
PILOT
DIAPHRAGM
SPRING
A
RP972A
2
BRANCH
EXHAUST
4
B
RP972A
2
BRANCH
EXHAUST
4
C
C4296-1
N.O. VALVE
3-8 PSI
(21-55 kPa)
RP972A
N.O.
HOT WATER
4
1
2
3
N.O. VALVE
3-8 PSI
(21-55 kPa)
N.O.
CHILLED
WATER
95-7148EF
C8124