What is a Quarter Turn Electric Actuated Valve?
Electric actuated valve is a kind of rotary (quarter turn) valve (such as Butterfly, Ball valve) actuators used to control Quarter (0-9°) turn valves. These actuators convert electrical energy into a kind of rotary motion. The movement of quarter-turn motors is limited between 0-90°. The torque created by the electric motor is transmitted to the output shaft by a drive gears. Electric actuators can be controlled by AC (alternating current) or DC (Direct current). Gears, shafts, limit switches, motor and other components are gathered in a compact body. Connection parts and norms containing ISO5211 connection standards are applied in electrically actuated valves.
Quarter Turn Electric Actuated Valve – Torque
Electric actuated valves require a 90 degree turn for opening and closing. The torque value produced by the motor is transmitted to the valve connected to the output shaft in Nm. An actuator torque is dependent on engine power and gear design. In order for the actuator to open and close the valve, the torque value it has must be 30% higher than the valve torque. Valve Breakaway is specified as the required torque for a valve as it is the highest Torque required to rotate the valve.
Click to view 4-20mA Proportional Electric Actuated Valve
Breakaway Torque
When a valve is in the open or closed position, the torque value required to separate from these points is called the disconnection torque. In other words, it is the torque value required for a valve to start moving from the stopping point. In general, the release torque for ball valves is 30% higher than the operating torque. Since the motion starts from a stationary point, the fluid may create a misalignment on the sphere, and the sphere may create friction on the seat surface. Therefore, the settling torque is higher than the operating torque.
Electric Actuator Response Time
Response time is defined as the time a valve needs to fully open or close after command. The speed of a motor is directly proportional to the power of the motor and the gear design. With an actuator motor capacity and higher gear ratios, more torque can be produced while a lower response time can be achieved.
Control Types of Electric Actuator
In electric actuators, the control signals are collected in 3 main groups as two step (ON-OFF), 3 Point Floating control (3-point control) and Proportional (modulating) control. In recent years, some communication protocols have started to be used with technological developments. Standard supply voltages of these motors are 24 VAC, 24 VDC and 220 VAC, 380 VAC.
Installation of Electric Actuators
Quarter-turn actuators feature a square flange connection so that it can be attached to the valve.
These connections are designed in accordance with the ISO 5211 norm. There are different types of flanges in the ISO 5211 standard that vary in maximum flange torque, size and number of screws, bolts or studs.
Features of Quarter Turn Pneumatic Actuators
Position Indicator
The position indicator shows the open and closed position of the actuator at a given position. There are also electrical systems that can send position information in the form of dry contact, as limit switches or as 4-20 mA as aolog. Position indicators have 2 different modes of operation. One of them is mechanical switches, the other is Proximity (non-contact). Mechanical switches are activated by a camshaft. Proximity switches are activated by sensors that detect valve position.
Manual (Hand) Control
The hand control is a safety feature built into actuators. The hand control allows us to intervene in the valve in case of a power cut (error) or an emergency.
Working Cycle
The Duty Cycle determines the operating time of an actuator between cycles. Opening and then closing the valve is called a cycle. The operating cycle is expressed as a percentage and is considered a ratio of on and off time.
Safety Position (Fail – Safe)
It is a safety element applied in case of power failure or failure in the valves. Depending on the characteristics of the process, it is ensured that the valve remains open or closed according to the system safety in automatic valves. These safety positions, spring mechanism or energy storage systems, which can be batteries, capacitors, enable the valve to be brought to the desired safety position after power cut. An example of this application is that the steam valve is closed to prevent overheating, while the cooling water valve remains open to prevent overheating.
ELECTRICAL CONNECTION
Two Point (ON-OFF) DC Connection
The + or – of the DC voltage is the common terminal, and depending on the common terminal, the other terminal is directed to the other two terminals via its contacts via a digital control device and opening and closing is provided. The actuator consumes power only when energized.
Two or Three Point Floating Control DC Electrical Connection
Two Point ON-OFF AC Connection
IP PROTECTION CLASS
IP Protection class indicates the degree of protection of the electric actuator against water, dust and environmental effects. The standard protection degree of electric actuators in ball valves is IP54. Some manufacturers can provide IP65.
ATEX
Atex directives specify the operating conditions of actuators in explosive atmospheres. It is defined as an explosion-proof actuator.
LVD Low voltage Directive 2014/35/EU
Indicates that electric actuators are protected against low voltage.
ELECTROMAGNETIC COMPATIBILITY (EMC) 2014/30/EU
It shows that the actuator does not create an electromagnetic field and is not affected by the electromagnetic field.
WHAT IS ELECTRIC ACTUATOR VALVE MATERIAL?
The bodies of electric actuators are generally produced from plastic derivatives or aluminum alloys. Different materials can also be used according to the characteristics of the application.
Selection Criteria of Electric Actuators
- Torque Value
- Motor Power
- Connection Types
- IP Protection degree
- Temperature
- Atex
- Safety Position
- Process application type
- Working Cycle