Fail-Safe Actuators - KMC Controls

September 6, 2013 – 11:09
DOOR LOCK ACTUATOR | AllElectronics

When Failure Is Not an Option: The Evolution of Fail-Safe Actuators Fail-safe actuators are those devices that return to a home position if the electrical power or pneumatic pressure supplied to the actuator is lost. Such actuators are often used on crucial damper and valve applications that require protection from excessive temperatures, such as preventing coils from freezing or rooms from overheating. They are required on most steam valve applications.

Back in the days when pneumatics ruled commercial HVAC controls, fail-safe protection was easy because pneumatic actuators are inherently fail-safe. Air pressure pushes on a diaphragm that compresses a spring and drives the actuator’s pushrod. When air pressure fails, the spring automatically returns the diaphragm and pushrod to the normal, home position.

When electric actuators began replacing pneumatics, however, they had no inherent fail-safe return. When power was lost, they were stuck in whatever position they happened to be in at the time. To remedy that, concepts from the old pneumatic spring technology were used to make spring-return fail-safe electric actuators. As an electric actuator drove a load, it also tensioned a spring. To maintain position, power had to be continuously supplied. When the electrical power failed, the spring would return the actuator to its home position. To make a fail-safe version of a particular standard electric actuator, however, the torque had to be essentially doubled to overcome the resistance of the spring in addition to the load.

Spring-return actuators have been around for a long time, and building specs sometimes still state that traditional spring-return actuators be used. But a newer, more convenient, more durable, more consistent, more energy efficient, and more economical solution for electric fail-safe is to use, instead of springs, capacitors that are continuously charged whenever power is applied. When electric power fails, the charge in the capacitor is used to drive the actuator back to its home position. KMC capacitor-driven actuators include the MEP-537x and MEP-7x5x models.


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Source: www.kmccontrols.com

KMC Controls Actuator, Tri-State, Failsafe, 320 Lbs
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  • Capacitor-Driven

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APEM Red Harsh Environment Push Button Switch
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TE Connectivity TE CONNECTIVITY / POTTER & BRUMFIELD - W92-X112-30 - CIRCUIT BREAKER, HYD-MAG, 2P, 277V, 30A
BISS (TE Connectivity)
  • Circuit Breakers 30A 2 POLE 2 TOGGLE
  • Hydraulic Magnetic Circuit Breakers
  • Current Rating:30A, Voltage Rating: 277VAC, Number of Poles: 2 Poles, Actuator Type: Toggle
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Electroswitch Inc. E4C0305N Switch, Rotary; 3 Poles; 2-5 Pos.; 1 Sec.; Ceramic Ins.; Non-Shorting; 11A; 28VDC; Solder
BISS (Electroswitch Inc.)
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