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8 SETTING OF TORQUE LIMIT SWITCHES
Actuators are set and tested in accordance with the torque stated on
purchase orders.
If no torque is specified, the actuator is supplied with torque springs
set to the nominal torque (refer to our Technical Handbooks).
SQX and STX6 models
IMPORTANT: the torque limit switch design of SQX/STX6 actuators
gives a short duration contact only (signal has to be memorised).
If this torque setting must be readjusted, please consult us.
STX models (except STX6)
Remark: The STX torque limiter provides a maintained contact
If the torque limiter is activated during an operation, check:
- that the valve stem is clean and well lubricated
- that the valve stem does not jam in the nut
- that the valve stuffing box is not too tight
If the torque limiter setting has to be modified, consult the valve
manufacturer before proceeding as follows:
- open the limit switches compartment (cover with mechanical position
indicator)
- the torque limiter shall be released prior to proceed to any adjustment
- according to the valve travel direction, determine which adjustment screw to use
- Turn the setting screw to set the new torque limit value reported on the A to G graduated
scale. The A corresponds to the nominal torque of the actuator (100%). Depending on the nomi-
nal torque and the reference, the percentage of torque per gradution (A to G) will be diffrent.
Please refer to the table at the end of the document.
9 MECHANICAL POSITION INDICATOR
The indicator disc is driven by the camblock system.
Turn electrically the valve to the completely closed position and rotate the
disc until the symbol and the arrow are lined up.
Turn electrically the valve to the completely open position to check that
the symbol and arrow are lined up. Adjust if required.
10 POSITION FEEDBACK POTENTIOMETER (OPTION)
The potentiometer used for actuator signal feedback is driven by the travel
cam block system. Unless special configuration, the potentiometer has a total resistance of 1000
Ohms 1W. Its operating range depends on the valve travel (typically 730
to 1000 Ohms).
The potentiometer has no mechanical stop and has a non-resistive area
(dead zone) at both the beginning and end of track.
0% position corresponds to a closed valve. 100% to an open valve.
Setting of potentiometer zero is achieved thanks to the «0% postion»
screw.
Drive the actuator to the closed position.
Resistance value is measured between terminals 16 and 17.
Hold the pinion located just under the plate with the «0% position»
