Air Over Oil

Air over oil compressed air systems were developed to, unlike cylinders driven solely by compressed air, generate smooth, hesitation free and consistent movement of your air cylinder rods or carriages.

In using the stored energy in compressed air, we plumb that compressed air into air lines, through compressed air valves, and ultimately into an air cylinder or air actuator to do the work we want.

An air actuator converts the energy in the compressed air into linear or rotary movement.

Very Fast Movement!

Air moves from high pressure to low pressure incredibly quickly. I've heard that air flowing from your compressor tank down the air line 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, then so does the tooling on the end of the piston rod.

Speed Is Sometimes A Problem

Where the tooling is designed to impart blunt force, a piercing or cutting 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 can be accomplished by using flow controls.

Smooth Movement Is Not Always Possible

Changing conditions in your cylinder load (friction or sideloading for example), perhaps advancing seal wear inside the cylinder, periodic 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 using only a flow control.

As an air cylinder piston moves, each time anything 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 is worse, inconsistently.

The use of pneumatic flow controls can do much to reduce the 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, stroke after stroke, particularly at slower rod-travel speeds. If you need to have exact rod travel speed, and throught that, exact and repetitive tooling speed, just flow controls cannot do that.

Air Over Oil Equals 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 has cost ramifications as well as requiring operators to have a whole new set of skills.

An all-hydraulic system with hydraulic oil being used as the driving mechanism for a cylinder, 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... an air over oil system.

Here are details of an air over oil system and what such a system can do for you.