
SMB/SB Installation and Maintenance Manual
140-11000 • July 2003
4-3
Flow Control Division
Limitorque Actuation Systems
4.4 Setting The Limit Switch
a
WARNING: Disconnect all incoming power before opening or replacing the limit switch compartment cover.
CAUTION: When wiring control circuits, distinguish between “normally open” and “normally closed” terminals on the geared
limit switch.
CAUTION: Do NOT attempt to repair the limit switch gear box. Replace entire limit switch gear box.
CAUTION: Do NOT use abrasive cloth to clean the silver contacts on the limit switch. Contacts should be burnished.
CAUTION: Before motor operation, reset the geared limit switch if the actuator has been dismantled or removed from the valve.
NOTE: Clean the limit switch cover thoroughly and apply a thin coat of grease on machined flange surfaces before mounting on an
explosionproof actuator.
4.4.1 Two-Train Geared Limit Switch
The rotor-type, two-train geared limit switch employs two rotary drum switches. Each rotary drum switch contains four contacts.
When the rotor is properly set to trip at the desired position, two of these contacts open electric circuits and two of the contacts close
electric circuits. One rotor is normally set to trip at the full open position of the valve, and the other rotor is normally set to trip at the
full close position of the valve.
Each drum switch may be adjusted independently of the other:
• First Drum Switch—one circuit is used to open the “open” holding coil circuit of the motor controller, one circuit is used to
control the “open” indicating light.
• Second Drum Switch—one circuit is used to open the “close” holding coil circuit of the motor controller, one circuit is used to
control the “closed” indicating light.
For the geared limit switches to trip at any desired position, follow the setting procedure below.
Piece numbers refer to Figure 4.1 and Table 4.3.
1. Verify all power is OFF.
2. Using the handwheel, manually open the valve to the full open position. See Section 5.2 Manual Operation. Note the direction of
rotation of the Intermittent Gear Shaft (piece #42), located over the Rotor (piece #49) to be set.
3. Using a screwdriver, turn the Set Rod (piece #48) clockwise until it reaches a stop position.
4. If
the
Rotor (piece #49) you are setting has not turned 90˚ to open the contacts that should trip open at this position, insert
screwdriver on the Intermittent Gear Shaft (piece #42). Turn in the direction noted in Step No. 4 until the Rotor (piece #49) turns
and opens the contacts to be set.
5. If
the
Rotor (piece #49) has turned so that the contacts are already open, turn the Intermittent Gear Shaft (piece #42) in the
opposite direction as previously noted in Step No. 4 until the contacts close. Turn the Intermittent Gear Shaft (piece #42) slightly
in the direction noted in Step No. 4 until the contacts open. The Rotor (piece #49) is set at the correct position for contact
opening.
6. Back off the Set Rod (piece #48) until it stops. Place the screwdriver on the Intermittent Gear Shaft (piece #42) to ensure that the
shaft is tight and will not rotate. Do not force.
7. Close the valve completely. Repeat Step No. 1 through 6 to set the tripping position for the other Rotor (piece #49).