Hydraulics vs. Pneumatics: Actuator Speed

In hydraulics, the speed of an actuator depends on the amount (volume) of flow from the pump. If the pump provides more flow, the actuator will move faster. In pneumatics, the speed of the actuator is not affected by the pump flow (in this case, the pump is the air compressor), because the air compressor's flow goes into a storage tank to be used as needed by the system. Instead, pneumatic actuator speed depends on the amount of pressure at the regulator that is in excess of what is needed to overcome the resistances.

We learned that the two resistances in pneumatics are loads at the actuator and air friction. Once these loads are overcome, any additional pressure will determine the speed of the actuators. Simply put, increase in pressure equals increased speeds. We can also do other things to increase actuator speeds, like decreasing the load or the air resistance.

The following formulas prove these facts.

Formula: Excess Pressure

Px = PR - PAF - PL

Where

PX = Excess Pressure

PR = Regulator Pressure

PAF = Total air Flow Resistance

PL = Total Load Resistance

If Your Actuator Speed Decreases...

In troubleshooting, if you notice that your actuator has slowed down, there are three things that may have happened:

1. Your load resistance has increased
2. Your flow resistance has increased
3. Or your Regulated pressure has decreased

Any one of these 3 possible problems will cause your actuator speed to decrease.

If it Increases...

And on the opposite side, if your load resistance or your flow resistance goes down and your regulated pressure stays the same, your actuator speed will increase.

There is a limit to how fast air will move. When air speed, at any point in the circuit, reaches the speed of sound, an increase in excess pressure will no longer effect actuator speed.

Unless specified otherwise, any and all work on this survey is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.