Sp970 Operation - Honeywell Pneumatic Controls Engineering Manual

Switches

SP970 Operation

SP970 Typical Piping
BRANCH
2
M
1
EXH 4
SP970A
A. MANUAL POSITION APPLICATION
Operation
SP970A Three Port Switches
PRESSURE REGULATOR OPERATION
Main line air flows through the restriction into the branchline
chamber and out the nozzle. Branchline pressure increases
until it is strong enough to compress the spring and lift the
diaphragm off the nozzle. Air flow out the nozzle is controlled by
the balance between the branchline pressure and spring force.
See Typical Piping Diagram A Above.
MINIMUM POSITION OPERATION
See Typical Piping Diagram B above. An external signal is
connected to Port 4 (Exhaust Port). When the external signal is
greater than the spring load, the nozzle opens and branchline
pressure is the same as the external signal. When the external
signal is less than the spring load, branchline pressure is
controlled as described above. See Operation Diagram below.
SP970A operation
SP970
2
BRANCH
4
PILOT
MAIN
70 customer.honeywell.com
BRANCH
DAMPER
ACTUATOR
M
1 2
CONTROLLER
B. MINIMUM POSITION APPLICATION WITH
CONTROLLER INPUT
SP970A
2
BRANCH
4
1
PILOT
MAIN
DAMPER
ACTUATOR
2
M
1
4
SP970A
SP970C Four Port Switches
These minimum position devices have a separate dead-ended
chamber connected to Port 3 to receive an external signal.
When the external signal is less than the spring load, the signal
has no effect and functions similar to the SP970A as a pressure
regulator. When the external signal is greater than the spring
load, the spring load is isolated and the device duplicates the
input signal. See Operation Diagram below.
Piping Diagram C above shows a typical four-port SP970C
application. The minimum-position switch keeps the pneumatic
actuator at a minimum position until the thermostat pressure is
greater than the minimum position valves. The thermostat then
controls the actuator.
SP970C Operation
PILOT
CHAMBER
3
PILOT
BRANCH
2
A. BUILDING TO MINIMUM SETTING
1
C4298A
3
PILOT
BRANCH
2
B. BALANCED AT MINIMUM SETTING
70-6925
DAMPER
ACTUATOR
BRANCH
2
M
1
4 3
EXH
INSERTION
SP970C
THERMOSTAT
M
C. MINIMUM POSITION APPLICATION WITH
BLEED TYPE THERMOSTAT INPUT (LP916)
SP970C
DISC
3
PILOT
BRANCH
2
4 1
VENT MAIN
C. PILOT BUILDING BRANCH ABOVE
MINIMUM SETTING
SP970C
3
PILOT
BRANCH
2
4
1
VENT MAIN
D. BALANCED AGAINST PILOT
C4471A
SP970C
4 1
VENT MAIN
SP970C
4 1
VENT MAIN
C4300A