Air Over Oil
The free air we breathe (questionable quality that it is these days) is often sucked into the intake port of an air compressor as well.
The air compressor then scrunches (technical term alert!) free air into an attached air tank in such volume that the air pressure inside the air tank has no choice but to increase.
When the air pressure inside the tank reaches industrial compressed air levels; somewhere between 100 PSI - 150 PSI depending on the system, the compressor will stop compressing free air.
In using the stored energy in compressed air, we often then bleed that compressed air into air lines, through compressed air valves, and ultimately into an air cylinder to do work.
An air actuator converts the energy into some sort of linear or rotary movement.
Very Fast Movement!
Air moves from high pressure to low pressure incredibly quickly. It's been suggested that air flowing from your compressor tank will be moving at or near the speed of sound.That speed-of-air movement translates into very high speed operation of your air actuators. The piston inside the air cylinder barrel reacts almost instantly to the inrush of compressed air, and since the cylinder rod is attached to the piston, it reacts immediately too. And, so does the tooling on the end of the piston rod.
Sometimes A Problem
Where the tooling is designed to impart blunt force, a pierce or cut type of tooling for example, then high speed impact on the work piece is desired.That is not always the case.
Many applications for actuators require slowing the piston rod and tooling considerably so as not to damage sensitive tooling or the surface of the work piece.
Slowing and controlling the speed of the piston rod and tooling of an air cylinder is normally accomplished by using flow controls.
Smooth Movement
Changing conditions in your cylinder load (friction or sideloading for example), advancing seal wear inside the cylinder, pulsation from the compressor or other variations in the supply air pressure, and other factors will contribute to varying cylinder rod speed and smoothness.It is the variability of compressed air (that air can be compressed at all, and the energy stored in tanks) that prevents an air cylinder from operating with consistent speed and smoothness.
As an air cylinder piston moves, each time something inhibits the piston, rod or tooling travel - even by a little bit - there will be a momentary hesitation in that travel as the air pressure inside the cylinder fights to overcome that inhibition. Cylinder rod speed and rod-travel timing will, as a result, change continuously, and what's worse, inconsistently.
The use of pneumatic flow controls will do much to reduce the impact of the speed and stroke time variations in the travel of your cylinder rod. Due to the nature of compressed air, flow controls alone cannot ensure that your cylinder stroke and timing will be consistent all the time, particularly at slower rod-travel speeds.
Smooth Cylinder Actuation
If you need consistent and smooth operation of a linear actuator, then you have a number of alternatives.Move from using compressed air entirely and obtain an electric linear actuator. This option cost ramifications.
Or, consider an all-hydraulic system. With oil being used as the driving mechanism for a cylinder, you can impart consistent and smooth movement to the hydraulic cylinder rod movement. This solution, too, has cost issues; the need to acquire a hydraulic power pack, among other accessories being part of those considerations.
A Hybrid Solution
This brings us to an excellent solution for imparting consistent, smooth operation to the cylinder stroke; a hybrid solution... and air over oil system.Here are details of an air over oil system.
