Honeywell ml7420 User Manual

ML6420, ML7420 NON-SPRING RETURN ELECTRIC LINEAR VALVE ACTUATORS

63-2533—03

Auxiliary Potentiometers

The 43191679 Auxiliary Potentiometers can be used as

feedback potentiometers and to provide remote indication of

valve position. See the Installation Instructions packed with the

potentiometers.

Auxiliary Switches

The 43191680 Dual Auxiliary Switch can be used on both the

ML6420 and ML7420 Electric Linear Valve Actuators. Switching

points are adjustable over the full length of the actuator stroke;

for example, the switch can be used to switch pumps or to

provide remote indication of any stroke position. See the

Installation Instructions packed with the auxiliary switch.

CAUTION

Equipment Damage Hazard.

Improper voltage damages the auxiliary switch

beyond repair.

Use the 43191680 Dual Auxiliary Switch only with

24 Vac applications.

OPERATION

General

In the actuator, the drive of a synchronous motor is converted

into the linear motion of the actuator stem by using a spur gear

transmission. A button retainer clip connects the actuator stem

to the valve stem.

Manual Operation

The ML6420 and ML7420 are equipped with a manual

operator knob (see Fig. 14) to open or close the valve in the

event of power failure:

1. Turn off or disconnect the power supply before manually

operating the actuator.

2. Push down on the manual operator knob and turn the

knob:

a. Counterclockwise to drive the stem downward.

b. Clockwise to draw the stem upward.

IMPORTANT

Manual operation allows very high closing force that

can jam the actuator spindle, exceed the force switch

ratings, and stop the motor. After a manual valve

close-off operation, release the spindle one turn by

turning the manual operator knob. This will ensure

automatic disengagement of the manual operator

upon power resumption.

NOTE: If the manual operator knob is not pushed in while

turned, it will rotate only a short distance before

disengaging without power resumption.

Fig. 14. Manual operator knob.

ML7420

Signal Input (+)

The analog input signal (+) range is set at the factory to 0 to 10

Vdc. Changing the position of the W2 selector plug sets the

range to 2 through 10 Vdc. Selector plugs W1, W2, and W3 are

positioned on the back side of the printed circuit board. See

Fig. 12 for location of the selector plugs.

Signal Input Failure

Using the potentiometer, the actuator can be set to run to any

position in event of a signal failure (ML7420/25 only). ML6420

does not have any input signal failure jumpers or

potentiometers.

Output Signal Feedback (F)

An analog output signal (2 to 10 Vdc) that represents the actual

actuator stem position is available at terminal F. It can be used

for remote indication of the stem position. When the actuator

stem is fully downward, the output signal is 10 Vdc.

When the valve stem is up, the output signal is 0 or 2 Vdc. The

output of the signal does not change when the action of the

actuator is reversed using W3. See Direction of Action.

Actuator Override

To override the control signal (for freeze protection or similar

applications), connect the 24 Vac common (T2) to either

terminal O1 or O2. Connecting to terminal O1 fully extends the

actuator stem. Connecting to O2 fully retracts the actuator

stem.

The control signal (+) is ignored when the override signal is

applied to terminal O1 or O2. This override can be achieved

with a switch or a relay. See Fig. 15.

M6640