Excerpt: Determining which actuator fits the application best is a consideration of budgetary requirements and fitting the right type of actuator to the use case.
Determining which actuator fits the application best is a consideration of budgetary requirements and fitting the right type of actuator to the use case. Applications considerations for each type are further explored below:
Manual Actuators Determining
Manual actuators must be a traveling nut, self-locking type, and be designed to hold valves in any position (between fully open and fully closed) without creeping/fluttering. They are usually equipped with mechanical stop-limiting devices to prevent travel of the disc in open/closed positions. Valves close with a (clockwise) (counter-clockwise) rotation. Designed to produce the specified torque with a maximum pull of 80 lb. on the handwheel/ chain wheel. Actuator components withstand input force of 610 Nm. at extreme actuator position without damage.
Manual Geared Actuators
Gear actuators limit pull force to 80 lbf (360 N). Maximum lever length or handwheel diameter is further limited by industry specifications. There are a variety of gear actuators with different functions. Utilizing the following steps can determine the ideal gear type for the project:
- Know the valve type that is operated
- Evaluate environment effects on the gearbox
- Consider the frequency of automation
Electric actuators must be sized to guarantee valve closure at the specified pressure and temperature. They are capable of operating temperatures ranging from -22°F to 158°F. The motor requires low inertia, high torque design, and class F insulation. Recommended torque setting of 40-100% rated torque. Torque output ranges from 10 Nm to 2260 Nm. Electric motor voltages typically range from 12 to 24 volts for DC and 24, 120, and 220 volts for AC. These types of actuators typically pair with a high-end valve such as a butterfly valve or Orbit valve.
Pneumatic actuators primarily utilize painted aluminum alloy for end caps and a stainless steel drive shaft. Temperature ranges from -4°F to 176°F with dry air as media. Supply air pressure ranges from 40-120 psi (spring return) and 20-120 psi (double acting). Torque output varies per model, from 400 Nm. – 6700 Nm. Service life provides up to 1 million cycles.
Hydraulic actuators are designed to carry linear movements for forces from 10-250 kN. Supplied with multi-grade oil as standard. Allows operation at temperatures of – 13 °C to 50 °C. Push or pull force must be lower than 980 N in any case. Acceptable leakage within min=0.05 Litres/min and max=2 Litres/min. Must be able to tolerate the pressure of 4270 psi for 15 minutes (minimum) with no leakage.
A solenoid actuator typically has one of the following power requirements: 120 VAC, 240 VAC, 24 VAC, 12 VDC. Supply pressure varies from 20-120 psi and operates in temperatures between -40 to 140°F. Standard features include manual override and mechanical spring safety position.
Spring actuators have a standard working temperature of -22°F to 212°F and are sized for 80 psi minimum for pistons and 35 psi for control valves. The body is primarily aluminum and could be hard anodized and epoxy coated. Due to its role in preventing power failure, specifications of this vary for each actuator type.
Repair and Maintenance Considerations Determining
Valve issues can affect the functionality of the actuator and aggravate underlying problems. Typical valve issues that cause actuator problems are listed below:
- Worn out the valve stem
- Seized up packing
- An obstruction
- Too much torque
Before attempting to fix an actuator, it is crucial to check the valve for any issues. To do so, put the unit into manual override and try to operate the valve manually (for electric). If the valve remains stagnant it is a valve issue, but if it operates in manual mode the actuator requires repair.
An actuator has four major components that can break down: the center column drive, connection to the valve, the contactor, and the motor.
Center Column Drive
The center column drive is responsible for closing and opening the valve. Rare occurrences can cause this drive to break. Generally, it is not the main cause of actuator issues. Replacement of center column drive requires removal of the actuator from service before repair.
Connection to the Valve
The drive nut serves as the main connection to the valve and is common to fail. A broken actuator drive nut will be unable to move the valve stem properly. This is viewable by removing the center column cover and looking down the center to the valve stem.
COURTESY C3CONTROLS Determining
The motor contactor is an electric actuator internal electrical part that controls the open/close motion of the valve when given an input signal. Failure of the contactor prevents actuators from operating. Fuses around the contactor should be checked prior to a full inspection.
In electric actuators, the motor provides torque to open and close the valve or other piece of equipment. If the motor fails, no movement will occur. In this case, the duty cycle and insulation class must be validated as sufficient for the application.
Regular maintenance can increase reliability, lower maintenance costs, reduce the chance of potential major shutdowns, and prevent operability loss. The following maintenance procedures are suggested:
- Check and replenish oil level
- Conduct inspection of all external surfaces
- Check mounting bolts, nuts, washers, and screws for damage/tightness
- Confirm correct hand wheel operability
- Signs of deterioration
- Check connections for tightness
- Inspect the motor for ingress of moisture
- Inspect motor peckerhead to ensure snug connections
- Replace ‘O’ ring seal
- Replace all cover screws and apply grease to prevent corrosion
- Validate local and remote operation