The debate between hydraulics and pneumatics is one that has garnered a lot of attention over the years. The field of fluid power has advocates on both sides that swear that one technology is infinitely better than the other. Both use a very similar type of motion, and they use fluid to transmit mechanical energy. Additionally, the executions use the same basic terminology, symbols and components. As a result, there is a lot of confusion about each type of fluid power.
Consider that both hydraulic and pneumatic systems require the use of a pump. However, compressed air has to be stored in tanks before it is transmitted to the pump for use. Additionally, both systems use valves in order to manage the level of force and velocity of the actuators. Essentially, the only real difference between the two types of power is the medium that is used.
If you imagine an indestructible container existed in this world that was filled with a liquid and you began to compress the liquid using a high-powered plunger, the most likely scenario is that you simply couldn’t compress the water. The truth is that liquid is compressible to a small degree. In the case of hydraulic oil, you can compress 0.5 percent for every 1000 PSI that is asserted on the liquid. However, this is an impractical consideration for anything other than theory. The truth is that if you begin to press a large quantity of oil into a fixed volume container, the pressure will begin to increase. The inevitable result is that something will have to give.
When you use non-elastic oil to transmit mechanical energy, you’ll get a highly efficient method of transmission. In this scenario, there isn’t much energy that is lost in a scenario where fluid is compressed. You’ll be able to pull a lever, and the actuator will engage immediately without needing to worry about any changes in fluid compression. In fact, a column of oil in this scenario would move much like moving a piston in a car engine.
The drawback to non-elastic oil is that it is very difficult to transfer it through valves, plumbing and other components. The flow of liquid will naturally be restricted, and there will be more energy lost than in the case of pneumatics. This restriction can be overcome fairly easily, but it requires the use of properly sized components that are matched to handle the systems flow.
There is another advantage of using hydraulics in applications. The resistance of the oil to changes in volume increases its power density. When you run a hydraulic system up to 10,000 PSI, there is very little decrease in performance compared to a pneumatic system at even 300 PSI. An air compressor can only compress so much air, and even a multi-stage compression chamber can result in lost energy to heat.
The application that you’re going to use is an important consideration when deciding whether to use hydraulic or pneumatic systems. Compressed air has capabilities that oil simply can’t provide. The ability to compress air offers a distinct advantage since its release results in a large amount of power. There is a large volume of air that can be forced through pneumatic valves at lightning speeds, which results in increased velocity of pneumatic actuators.
Under the guidance of a properly trained technician, a pneumatically actuated machine can provide outstanding speed and a quick response. Light manufacturing jobs and assembly applications are generally the best application for pneumatic machines. However, the sheer power of a hydraulic machine can’t be ignored. A hydraulic machine is capable of blowing away a pneumatic machine as it can produce thousands of tons of force in contrast to the thousands of pounds offered by pneumatics.
When it comes down to it, the difference between pneumatics and hydraulics is really all about the medium that is used. The mathematics of applying these two fluid power devices involves slightly different calculations. For example, a hydraulic system is most concerned with the ratio of compression while pneumatic compression doesn’t matter. Ultimately, if you ask a hydraulic specialist about pnuematics and vice-versa, you’re likely to get several different answers.