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Actuators

Valve Actuators Pneumatic Electric Hydraulic

A wide range of subsea mechanical gears and hydraulic actuators (linear and quarter turn) tailored to meet Customer requirements with the highest level of performance and reliability.
Valve actuator is a mechanical component \ device used to operate the valve using power source. It can be Manual, Electric, Pneumatic, or Hydraulic. There are two main types of actuators Rotary and Linear.
Rotary Valve Actuators: It produces the rotational motion needed to operate rotary valves such as ball, plug, and butterfly valves.
Linear Valve Actuators: It produces linear motion to operate such type of valves: globe, gate, and pinch valve.

Manual Actuators

• Basic Lever Actuator: The most common manual operator on smaller quarter-turn valves
• Hand Wheels: used for larger valves that require high torque to operate often incorporate geared hand wheels, (have a large hand wheel with a gearbox that further increases the mechanical advantage). These wheels will require multiple revolutions to turn the valve only 90 degrees.
• Manual Valves with Limit Switches: Many times, manual valves perform a function that does not require automated actuation, but the system still needs to know what position they are in.

Limit Switches: (position indicators) switches are used to communicate the valve’s current position to the control system. It can either be a mechanical device or a proximity switch, referred to as a “prox switch, can send a confirmation signal to a PLC (Programmable Logic Controller) or a DCS (Distributed Control System) to let the computers know if the valve is open or closed.

Pneumatic VS Hydraulic VS Electric Actuators

Pneumatic Actuators: utilize compressed air to generate the operating energy. These actuators are quick to respond, but are not ideal for environments under high pressures, as gas is compressible.
Hydraulic Actuators: operate similarly to pneumatic actuators, but an in-compressible liquid (Hydraulic Fluid) from a pump rather than pressurized air moves the cylinder.
Electric Actuator: converts electrical energy into torque using electrical motor.

 

Pneumatic Actuators pros and cons

Pros of Pneumatic Actuators:
Benefits of pneumatic actuators come from their simplicity, they generate accurate linear motion, its applications involve areas of extreme temperatures (-40°F to 250°F).
1. In terms of safety and inspection, cause of using air, pneumatic actuators avoid using hazardous materials
2. From explosion protection point of view and machine safety requirements because they create no magnetic interference due to their lack of motors.
Cons of Pneumatic Actuators:
1. Pressure losses and air’s compressibility make pneumatic less efficient than other linear motion methods.
2. Compressor limitations mean that operations at lower pressures will have lower forces and slower speeds and compressor must run continually operating pressure even if nothing is moving.
3. It must be sized for a specific job what means they cannot be used for other applications.

 

Hydraulic Actuators pros and cons

Pros of Hydraulic Actuators:
1. They are suitable for high pressure applications where they can produce forces 25 times greater than pneumatic cylinders of equal size. They also operate in pressures of up to 4,000 psi.
2. Hydraulic actuator can hold force and torque constant without the pump supplying more fluid or pressure due to the incompressibility of fluids
3. They can have their pumps and motors located a considerable distance away with minimal loss of power.
Cons of Hydraulic Actuators:
1. Leak of fluid, loss of fluid leads to less efficiency, leads to cleanliness problems and potential damage to surrounding components and areas.
2. Hydraulic actuators require many companion parts, including a fluid reservoir, motors, pumps, release valves, and heat exchangers, along with noise reduction equipment.

Electric Actuators pros and cons

Pros of Electrical Actuators:
1. Electrical actuators offer the highest accurate control positioning an example of the range of accuracy is (+/0.000315 in)
2. Electric actuators can be networked and reprogrammed quickly. They offer immediate feedback for diagnostics and maintenance.
3. They provide complete control of motion profiles and can include encoders to control velocity, position, torque, and applied force.
4. Environmental hazards are eliminated because there are no fluids leaks.
Cons of Electrical Actuators:
1. Electrical actuators are not suited for all environments, unlike pneumatic actuators, which are safe in hazardous and flammable areas.
2. The chosen motor just suits actuator’s force, thrust, and speed limits to a fixed setting. If a different set of values for force, thrust, and speed are desired, the motor must be changed.

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