An Overview of Valve Actuators – Pneumatic, Hydraulic and Electric

Actuators are devices that perform a simple mechanical task – they open and close valves. While the simplest and the least expensive way to operate valves is manually, it is not always ideal. Harsh and toxic operating environments are perfect examples of situations where automatic actuators are required. Automatic actuators also become necessary when a large number of valves have to be operated and/or when the operation requires changing valves very quickly.

There are three main types of automatic actuators – electric actuators, pneumatic actuators, and hydraulic actuators. While all three perform the same function, each type is suitable for specific applications. Here are a few ways in which they differ from each other.

Pneumatic Actuators: This mechanism uses air pressure to operate valves. The energy of compressed air is used to push a piston or a diaphragm, which in turn acts on a valve.

Advantages:

• They are simple to operate and maintain.
• They are cost effective based on the scale of operation.
• They are safe to use in a wide range of operating conditions.

Disadvantages:

• The gas/air used to operate the pistons is lost every time a valve is opened or closed.
• Even a slight drop in pressure can render the actuator inoperable.
• For this reason, every pneumatic actuator has to be sized for a specific valve operation.
• The gas chamber has to be located close to the actuator to generate the required pressure.
• Cost of compressed gas is an additional expense.
• They can only be used on linear and quarter-turn valves.
• They are not as precise as electric actuators.

Hydraulic Actuators: These work by replacing the compressed air with fluid pressure (pressure exerted by a fluid that cannot be compressed).

Advantages:

• Hydraulic actuators are significantly more powerful than pneumatic actuators (capable of exerting 1000s of psi of pressure).
• The fluid reservoir can be placed further away from the actuator without any significant loss of pressure.

Disadvantages:

• Fluid leakage is a concern. It can result in loss of pressure and make maintenance difficult.
• Leakages can become an environmental or safety hazard. Hydraulic fluids are not safe to use in certain operating conditions.
• Their complex construction makes them expensive and difficult to maintain.
• They can only be used on linear and quarter-turn valves.
• They are not as precise as electric actuators.

Electric Actuators: These actuators use electric motors to open or close valves. The torque generated by the motor is used to turn the valve mechanism.

Advantages:

• When you need a high degree of control while closing or opening valves, electric actuators are ideal since they can be operated with precision.
• The movement of the screw can be preset and the valve closing and opening action can be repeated quickly.
• Leakage of fluid or gas and the associated toxic hazards are not a concern.

Disadvantages

• They need electricity to run. You can replace this with battery power where needed.
• They cannot be used in certain environments due to the risk of fire.

For more information on valve actuators and other industrial equipment to suit your needs, call our toll-free number 1-800-367-4180.