IMO 11/19
12
IMO-553 EN
6.
Declutchable Manual Override (DO)
The DO_ is a declutchable manual override quarter turn
gearbox for single/double acting pneumatic actuators. To
prevent damage, it must be ensured that the actuator is not
operating, or able to operate, the gearbox when switching
from auto to manual or when operating the gearbox in
manual mode. NOTE: The following instructions reference
a fail closed (clockwise to close) installation, but a fail open
installation is also possible.
6.1
Installation
1. It is recommended to mount the handwheel on the
input shaft prior to assembling the gearbox to the valve.
2. Verify that the flanges on the gearbox and valve align.
Also verify that the valve stem and the bore of the
gearbox driveshaft match.
3. Make sure the valve is in the fully closed position.
4. Make sure that the gearbox is in the fully closed position
(as standard from the factory). This is achieved by
turning the handwheel clockwise.
5. Screw the stud bolts into the bottom flange of the gearbox
prior to mounting the gearbox on top of the valve.
NOTE: use of a gasket/sealant on the flanges between
the valve/ gearbox and between the gearbox/actuator is
recommended.
6. Mount the gearbox perpendicular to the valve and
secure the fasteners.
7. Follow the “Stop screw adjustment” procedure.
8. Position the driveshaft on top of the gearbox
9. Mount the actuator on top of the gearbox.
6.2
Stop screw adjustment
1. Remove air from the actuator and ensure the valve/
actuator/gear are in the fully closed position.
2. Put the gearbox in manual-mode by turning the handle
counter clockwise as shown in Figure 23 below. First
pull the knob (1) then turn the selector (2) and then
release the knob (3) and make sure it is engaged.
3. Turn the handwheel clockwise to put the gearbox/
valve in the fully closed position. When the fully closed
position cannot be achieved, loosen the stop screw-
close on the gearbox (Figure 23) and check the travel
stop adjustment of the actuator. Once fully open is
achieved, hand tighten the stop screw and secure with
the lock nut.
4. Turn the handwheel counter clockwise to put the
gearbox/valve in the fully opened position. When the
fully open position cannot be achieved, loosen the stop
screw-open on the gearbox (Figure 23) and check the
travel stop adjustment of the actuator. Once fully open
is achieved, hand tighten the stop screw and secure
with the lock nut.
5. Pull the knob outwards (3) then turn the selector (2)
toward auto until the knob falls back into its locked
position. The gearbox is now ready for operation.
6.3
Operation
1. The gearbox is delivered in automatic mode where the
valve is operated by the actuator.
2. To operate the valve with the handwheel, the gearbox
must be put into manual mode. Refer to Figure 23:
a. Vent the supply air from the actuator. Depending on
the instrumentation configuration there are multiple
ways to achieve this, 2 examples:
i. Adjust the supply regulator to zero
ii. Use the solenoid manual operator to exhaust the
air from the spring side of a single acting actuator.
i.e. ASCO 8551 solenoids with ‘MO’/’MS’, rotate the
manual operator screw from ‘0’ to ‘1’.
b. Pull the knob outwards (3) and hold the knob in this
position.
c. Turn the handle counter clockwise (2) toward “AUTO”
and release the knob. Continue turning the handle
until the knob falls back into locking position (1).
i. NOTE: When the handle cannot be fully turned
±90°, turn the handwheel slightly. Continue turning
the handle until full engagement is achieved (knob
returns to start position).
d. The gearbox is ready for manual operation.
e. Turn the handwheel clockwise to close the valve or
counter-clockwise to open the valve. The number of
turns needed to move from totally open to totally
closed is at least 8 turns and varies by model.
3. Declutch the gearbox to return to automatic mode:
a. Pull the knob outwards (3) and hold the knob in this
position.
Figure 23
