Exceeding Rated Duty Cycle (Burned-out Motor)
AC powered motors have “Duty Cycle” limitations. COVNA offers a standard duty cycle motor (25％) and an extended duty cycle motor (75％). The definition of duty cycle is the amount of time a motor can run relative to the amount of time it needs to be at rest.
Causes of excessive duty cycle:
1) Actuators on butterfly valves with no motor brakes. Solution: Install motor brake.
2) Standard duty motors in modulating applications. Solution: Use an extended duty motor.
3) Unstable control systems (constant modulation). Solution: Use DC motor (100%).
4) Multiple actuators wired in parallel. Solution: Use independent relays or Valvcon relay boards.
5) High temperature exposure. Solution: Shield actuator from heat.
Exceeding Rated Torque (Stripped motor gearbox)
The gear trains in COVNA actuators use rugged hardened steel spur gears. Under normal conditions, a gear failure is unlikely.
Causes of stripped gears in motor gearbox:
1) Manual override is not used correctly (“Push Down to Override”), thereby not declutching from the motor gearbox. Solution: Ensure proper usage
2) Over torque due to external influence or continuous stalling (gear fatigue). Verify actuator is sized correctly to the valve. Check Valve torque as it may have risen bevond published specifications and beyond actuator rating.
Incorrect wiring can simply cause an actuator not to run, or be as extensive as causing circuit board damage. Each actuator is supplied from the factory with an I.O.M. manual containing wiring information, as well as a built-in schematic on the “motherboard”. In adtion, miswiring can also be caused by working with the actuator’s internal connections (i.e. motor plugged into the board in the wrong spot, limit switches reversed, potentiometer plugged into wrong spot).
Out of Calibration / Out of “quadrant”
The manual override has the capability to put the actuator in any position relative to 360 degrees. If the actuator is turned such that it leaves the 90 degree quadrant it was set up for, it will lose it’s capabllity of positioning (many times the valve will not allow more than 90 degrees of travel). In addition, if the actuator is removed from the valve, and installed 90 degrees offset, this could cause “stalling” on butterfly valves or reverse logic on continuous rotation ball valves (what was open is now close and vice versa). COVNA actuators are marked on the output drive for position orientation. Position feedback potentiometer damage could occur outside the 90 degree quadrant.
Improper Environmental Protection (Moisture and Corrosion Damage)
There are three possible entries for moisture:
1) Override shaft – The override shaft incorporates an 0-ring seal.
2) Cover flange – All COVNA actuators are provides a gasket or an O ring and are NEMA4 rated.
3) Conduit entries – The conduit holes come factory plugged (plastic plug).
If the actuator is installed correctly (override shaft has O-ring, flange gasket/o-ring is in place, all cover bolts are tight, and conduit entries have been sealed), the actuator will be protected from splashing or hose directed water. For high humidity areas, we recommend installing the heater thermostat option (T).
Voltage Spikes (Burned-out Board, Burned-out Capacitor)
Voltage spikes caused by lightening or power surges can damage the electronic board circuitry. Install power conditioning and surge protection if required.
Old Age (Component Failure)
Components will fail due to old age and high use (over 100,000 cycles).
COVNA – Solve your technical questions with solid experience.
We are COVNA Automations, one of the top manufacturers of quarter turn actuators and automatic control valve products in Dongguan, China with 18 years experience. Our industrial experience will be useful in your business and projects.