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Frequently Asked Questions
How should torque be chosen?
Against the damper as it will be in twenty years.
Bearings stiffen and seals harden with age.
Dust accumulates in the linkage.
An actuator sized to a new damper eventually stalls.
Allow margin above the published requirement.
It costs very little at purchase.
What does a stalled actuator look like?
Nothing, which is the problem.
The damper stops short of commanded position.
The box delivers the wrong flow.
No alarm is generated by default.
Only comparing command against measured airflow reveals it.
Configure that comparison where possible.
Does the control signal type matter?
It must match the controller.
Analogue modulating, floating and bus types all exist.
Mixing conventions across an estate is a trap.
Stores end up holding three incompatible types.
Record which floor uses which.
Standardise where a refurbishment allows.
Why is fail position a design decision?
Because both failure modes have consequences.
Failing closed starves the zone of ventilation.
Failing open can overcool and unbalance the system.
Staying put defines nothing at all.
Spring return gives a known state and costs more.
Decide it deliberately, per zone type.
What limits actuator life?
Cycles, and the load it works against.
VAV dampers modulate constantly.
A stiff damper accelerates wear considerably.
Servicing the damper extends the actuator.
Manufacturers publish a cycle rating.
Compare it against expected modulation.
How is it mounted?
Directly on the damper shaft, usually.
Shaft size and length must match.
Anti-rotation bracket prevents the body turning.
A missing bracket destroys the mounting eventually.
Check shaft dimensions before ordering.
Adaptors exist and add backlash.
What access does replacement need?
A panel beneath the box.
Actuators sit above ceilings with other services.
Without a panel, replacement means building access first.
That converts an hour into a day.
Panels are omitted more often than not.
Record box locations at handover.