Reverse Action; Tp971B And Tp9610B; Tp971C; Tp971A And Tp9610A - Honeywell TP970 Series Manual

THROTTLING RANGE
ADJUSTMENT
BIMETAL
FLAPPER
NOZZLE
NOZZLE
CHAMBER
RESTRICTOR
MAIN LINE
Fig. 11. Operating Sections of TP970A, C and TP9600A
(Direct Acting).

Reverse Action

Refer to Figure 11. On a temperature rise, the flapper is
forced away from the nozzle by the action of the bimetal. The
force of the bimetal acting on the flapper is balanced by the
feedback force of the pilot pressure in the nozzle chamber
acting in an opposing direction. This action varies the
flapper-nozzle gap, which in turn causes a decreased
pressure in the pilot line. The change in pilot pressure is
routed to the flow amplifier that converts the low capacity
pilot pressure signal to a high capacity branchline flow at the
same pressure.
For a more detailed discussion, refer to the Valve Unit
Operation section.
TP971A-C AND TP9610A, B HIGH-
CAPACITY, DUAL-TEMPERATURE
THERMOSTATS
The TP971A, B, C and TP9610A, B Thermostats feature day
and night sensing elements with individual setpoint
adjustments for day/night control of heating and air
conditioning systems. The Thermostat cover is removable for
adjusting the nighttime setpoint. All TP971 and TP9610
Thermostats have a manual override lever (DAY/AUTO)
which allows the occupant to change the Thermostat
operation from night cycle to day cycle. The Thermostat can
be made tamper proof by cutting off the manual override
lever with a side cutter. The complete manual override lever
assembly can be removed and replaced if desired (see
TP970 and TP9600 Series Pneumatic Thermostats Service
Data 75-7134).
SETPOINT KNOB
CALIBRATION
SCREW
SETPOINT
CAM
PILOT LINE
FLOW
AMPLIFIER
VALVE
UNIT
BRANCH LINE
C6056-1
TP790 AND TP9600 SERIES PNEUMATIC THERMOSTATS

TP971A and TP9610A

On the TP971A and TP9610A direct-acting Thermostats (Fig.
12), the daytime bimetal controls the system when the main
air pressure is 13 psi (90 kPa). The nighttime element
controls the system when the main air pressure reaches 18
psi (124 kPa). Models are available with switchover
pressures of 16 to 21 psi (110 to 145 kPa) and 20 to 25 psi
(138 to 172 kPa).
NIGHT BIMETAL
NIGHT THROTTLING
RANGE ADJUSTMENT
DAY THROTTLING
RANGE ADJUSTMENT
THROTTLING RANGE
BIMETAL
ADJUSTMENT
FLAPPER
DAY/NIGHT
LOGIC CIRCUIT
Fig. 12. TP971 and TP9610 Day/Night Thermostat.

TP971B and TP9610B

The TP971B and TP9610B are the same as the TP971A and
TP9610A except that they are reverse acting.

TP971C

The TP971C is a direct-acting, three-pipe Thermostat. The
third pipe, a secondary branch line, is a switched line
providing pilot control of auxiliary equipment. Switchover
pressure is 13 psi (90 kPa) for daytime operation and 18 psi
(124 kPa) for nighttime operation. The TP971C is typically
used in conjunction with unit ventilator systems requiring
Day/Night/Warm-up cycles.
The secondary branch line is used with a pneumatic/electric
(P/E) switch to start and stop the supply fan on the night
cycle. The secondary branch line has full main air pressure
on the night cycle and daytime main air pressure on the day
cycle.
7
NIGHT SETPOINT
NIGHT SETPOINT
INDICATOR
KNOB
DAY BIMETAL DAY
SETPOINT KNOB
BRANCH LINE
PRESSURE GAGE PORT
NOZZLE
CALIBRATION
ADJUSTMENT
NIGHT
SETPOINT CAM
DAY
SETPOINT
KNOB
VALVE UNIT
AIR CONNECTION
FILTER AND
C6057
RESTRICTOR
77-9382—1