Greases and lubricating oils for pneumatic cylinders

Pneumatic cylinders are the most common actuators in compressed air systems. They are the primary means of pushing slides, lifting weights, clamping workpieces, powering equipment, removing workpieces and actuating levers.

The performance and service life of a pneumatic cylinder are conditioned by the integrity of the gaskets separating the pressure chambers. Their integrity is ensured by proper lubrication and assembly during fitting.
They are distinguished by:

Static gaskets – Concern sealing between elements of a cylinder between which there is no relative motion, such as between the barrel and cylinder heads. Static seals are effected by placing a deformable elastic element between the two pieces, mostly a toroidal seal of an O-ring variety.
Dynamic sealing rings – Intervene when a process involving the movement of organs is taking place. Typical dynamic seals are found on the pistons and cylinder rods. The gasket operation is based on the fact that the seal is forced against the surface on which the sealing takes place so that there is interference.

The sealing ring or gasket makes the most important contribution to the life and durability of the pneumatic cylinder, where the role of the lubricating grease can be decisive. What are the benefits of proper lubrication?

Reducing the coefficient of friction between the gasket and cylinder liner
Limiting lip seal wear
Resisting the leaching action of moisture in the circuit
Contributing to the maintenance of the gasket
Preventing the lubricant from changing the mechanical properties of the seal (swelling and streaking)
Reducing the demand for "air" and thus energy to move the cylinder

The lubrication of gaskets introduces an important yet often overlooked component concerning the potential chemical attack and consequent change in the structural properties of the compound, which can be translated into changes in size, hardness and sealing power.

The variety of design solutions for pneumatic cylinders is very broad, with there being guided, rodless, double-acting or single-acting and magnetically-driven compact cylinders. The design requirements, and thus also the choice of lubricant grease, take into consideration:

Length of the implementation strokes
Construction materials of the static and dynamic gaskets
Operating conditions (work load, actuation speed and operating temperature range)
Potential contact with process fluids (oxygen or media of an acidic, basic or organic nature)
Certifications for accidental contact with food

Equally important are any limitations in the use of lubricating solutions dictated by the application context of the cylinder, such as:

The presence of an oxygen-saturated atmosphere in the operating area of the cylinder
Use of the cylinder in equipment for applying coatings or paints

One of the most insidious threats in the operating environment of a pneumatic cylinder, typical of rubber-metal sliding friction, is the jerking motion. Commonly referred to as stick-slip, this manifests through an irregular cylinder stroke pattern, especially when changing direction – an undesirable phenomenon and the cause of intermittent operation, frequently caused by inadequate lubrication.