Consider a hydraulic system.
A hydraulic cylinder uses oil which is theoretically incompressible. With hydraulic flow controls lowering the cylinder speed and time-of-stroke below the available hydraulic force from the power-pack, you can be virtually certain of consistent stroking every time.
There are many circumstances, not the least of which is cost, that make an all-hydraulic system unacceptable. If that is the case, then the next option to deliver stroke-to-stroke consistent speed and timing is to use an air over oil system.
This system will use air pressure to drive oil into a cylinder and, since oil is not compressible, flow controls controlling the oil exiting the cylinder will ensure a smooth, consistent stroke every cycle.
European Type Brass Push-in Fitting
Brass pneumatic connector
Brass pneumatic coupler
An air Coil system will consist of:
-an air - hydraulic cylinder of choice
-two air - oil tanks
-two hydraulic flow controls
-a two position four or five ported air valve or two 2 positions 3-way valves
-necessary lines and fittings to connect the oil tanks to cylinder and valve to the oil tanks
-hydraulic oil
Check with the air cylinder vendor to ensure that their cylinder can be used in an air-oil application. Most can. The pressures generated are usually well within the safety factor for pneumatic cylinders which are much less costly than hydraulic cylinders.
Each of the oil tanks must contain enough oil to fill the cylinder during a complete stroke (an extension or retraction) without completely emptying the tank.
Each of the cylinder ports is connected to a fitting at the bottom of it's own oil tank.
The air valve is connected to the air/oil tanks, one working port to each tank. The lines are connected to the fitting on the top of the air C oil tank.
The oil tanks must be installed higher than the cylinder they are supplying. | 
