Selection of Shaft Seals for Oil-Free Compressors

Regarding the selection of shaft seals for oil-free compressors, based on relevant technical data and the characteristics of oil-free compressors, 

Twin-Screw Air Compressor Network provides a detailed introduction covering an overview of oil-free compressors and key points for shaft seal selection.

Overview of Oil-Free Compressors
Air compressors can be classified into oil-injected screw type, sliding vane type, centrifugal type and piston type. The definition of oil-lubricated and oil-free compressors depends on the oil content in compressed air after compression.

Some production processes demand extremely low impurity content in compressed air. Oil-free screw air compressors are widely adopted screw units, 

and they are also referred to as low-oil screw compressors. Large enterprises generally select two types of units:

Centrifugal compressors
Oil-free screw compressors (also categorized as low-oil screw compressors)
Centrifugal compressors adopt two-stage filtration. The final filtration accuracy reaches above 2 μm, and the filtration efficiency for particles above 0.4 μm is up to 90%.
Oil-free screw compressors deliver a final filtration accuracy of 10 μm. Additional after-filters shall be installed for systems requiring ultra-clean compressed air.

Select the appropriate compressor model according to the production process requirements of the industry. Practical application experience shows that the operating cost of oil-free screw compressors is slightly lower than that of centrifugal compressors. 

For industries with stringent requirements such as textile and pharmaceutical sectors, centrifugal compressors have to be prioritized for certain processes.

For your reference, the differences between oil-free screw compressors and oil-injected screw compressors are limited; the distinction is mainly reflected in professional naming standards. Fundamentally, 

almost all air compressors rely on lubricating oil for operation. Without lubricating oil, normal operation cannot be realized. Therefore, trace amounts of oil will inevitably exist in compressed air.

How to Select Shaft Seals for Oil-Free Compressors
In oil-free screw compressors, gas compression takes place in an entirely oil-free environment. Hence, reliable shaft seals must be installed between the lubrication zone and gas zone of the compressor.
The shaft seal shall not only operate efficiently under high peripheral speed, but also possess sufficient elasticity to accommodate potential axial movement of the rotor when sliding thrust bearings are adopted.