heat, noise, radiation, possible
explosive situation, corrosion,
space that is available, vibration,
seismic loading
; Orientation of the valve and actuator (horizontal or vertical)
; Speed of the operation—whether
it’s fast, slow or undefined
; Access for repair
; Cost of failure
; Process control requirements—
whether it’s on-off or modulating
(throttling/proportional control)
; Duty cycles
; Number of operations that occur—
both daily and as a total
; Required failure mode
; Position and performance of the
source and what diagnostics and
feedback is available
; Whether manual override is
required
; Whether emergency shutdown may
be needed
; The weight and center of gravity of
the actuator
; Mounting interface compatibility
Electric actuators (Figure 5) generally
provide the ability to stop at any point in
the travel. They also produce full-rated
output throughout travel. If electric is
used, you will need to match the required
electrical power (voltage, frequency and
available amperage) to what is available.
Temperature and surroundings will also
play a role. If an area is hot or wet, you
must assure the windings and housings
are appropriate. If fire is a possibility,
consider protective coatings/covers. For
corrosive atmospheres, assess the merit
of special paint coatings.
Typically, but not always, you will find
electric actuators:
; Offer constant output force torque
values
; Are typically constructed of aluminum, iron, ductile iron and/or
steel
; Are more limited regarding higher
temperatures
