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Hydraulic Systems - What You Need to Know About Actuators ben lee

When it comes to actuators, there are a few differences that you should know about if you’re in the engineering field. If you haven’t had a whole lot of experience, then here’s the lowdown.

Every mechanical movement system has a linear actuator in operation. It operates in a straight line but might be in the form of components, an assembly or a finished product. Used to perform the job of converting energy into movement or a force, an actuator might be powered by electricity, pressurised air or fluid.

Here’s what you need to know about the most common linear actuators, and what their pros and cons are.

How Actuators Work

Pneumatic line actuators. Consisting of a hollow cylinder with a piston inside, either a manual pump or an external compressor will move the piston. As pressure builds, a linear force is developed and the cylinder moves along the axis of the piston. It will then return to its original position using either fluid from the other side of it, or by a spring-back force.

Pneumatic actuators are really quite simple. They have bore sizes between ½ and 8 inches with a maximum pressure rating of 150 psi. So between 30 to 7,500lbs of force can be delivered. Steel versions can deliver forces between 50 to around 38,500 lb.

Because they don’t have any motors, and therefore produce no magnetic interference, they are often used in situations with extreme temperatures. You’ll find that they are very cost effective in addition to being lightweight and not needing of much when it comes to maintenance. Their components are durable as they aren’t under a lot of strain.

When it comes to disadvantages, they can suffer from pressure losses and therefore can be less efficient. Lower pressures equal slower speeds and lower forces. In addition, pressure must be made even if nothing is moving, so it’s necessary to continually run a compressor for them. For them to work most efficiently, they need to be sized for the job at hand and that makes them inflexible when it comes to other applications.

Hydraulic linear actuators. Working in a similar way to pneumatic actuators, this type of actuator is moved by incompressible liquid from a pump.

Being able to produce forces that are up to 25 times that of the pneumatic cylinder, they are considered to be rugged and well suited to high-force applications. The hydraulic actuator is able to hold force and torque without needing extra fluid or pressure sent through from the pump. Fluid is incompressible. This also makes it possible for hydraulic actuators to have both their motors and their pumps situated a distance away without suffering from loss of power.

The downside of the hydraulic actuator is that they can leak fluid and this can lead to them being inefficient. These leaks of hydraulic fluid can potentially damage components such as motors, fluid reservoir, heat exchanger etc…

Electric linear actuator. Powered by a torque converted from electrical energy connected to by a lead screw. As the screw rotates, either a ball or threaded lead nut will be driven along matching threads.

With the best precision control possible, the electrical actuator operates in a smooth and quiet fashion. They can also be reprogrammed and networked in a considerably short period of time. Without any fluid leaks, they are also less of an environmental hazard.

On the negative, each electrical actuator costs far more than that of either a pneumatic or a hydraulic actuator of similar power. They are also not suited to all areas either such as hazardous or flammable areas. There is also a danger that they can overheat due to having a continuously running motor.

Whichever motor is used is going to be reflected in terms of how much thrust, force and speed limits are required. If any of these need to be changed, then it will be necessary to acquire another motor.

As you can see for yourself, actuators come in 3 flavours, and it will depend upon your individual circumstances with regards to which one will give you what you need with the least disadvantages. 

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