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Water-lubricated oil-free compressors – advantages over dry-running oil-free compressors

In many sectors, including chemicals, pharmaceuticals, food processing and electronics, compressed air must be completely clean and free of contaminants. Oil-free compressors are therefore essential where oil contamination must be eliminated.

Published 26/08/2024

Water-lubricated oil-free compressors – advantages over dry-running oil-free compressors – PEMA photo

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There are several types of oil-free compressors. Dry-running compressors use two rotating screw or tooth elements. Water-lubricated compressors use water for sealing and cooling. Scroll compressors provide quiet, efficient operation at lower capacities. Turbo compressors suit large air volumes. Each technology has specific advantages for different industrial applications.

This article focuses on the advantages of water-lubricated oil-free compressors compared with dry-running oil-free compressors.

High efficiency and low specific energy consumption

Efficiency is a key factor when choosing a compressor. Water-injected compressors offer several important advantages over dry-running oil-free designs:

Lower operating temperature:

Water-injected compressors typically operate at around 60 °C, while dry-running oil-free compressors reach 200–300 °C, often causing premature wear or failure of sensitive components. Lower temperatures also improve isothermal efficiency, reducing energy consumption and increasing compression efficiency. Discharge air temperatures are lower too; dry-running technologies have discharge temperatures of 180–280 °C.

Lower speeds and less noise:

Water-injected compressors typically run at around 3,000 rpm, compared with 10,000–20,000 rpm for dry-running technologies. Lower speeds mean less noise and vibration, improving the workplace and reducing wear.

Direct drive and minimal mechanical losses:

Water-injected compressors use direct motor drive, eliminating the gearbox and timing gears typical of dry-running designs. This minimises mechanical losses and increases overall efficiency.

Eliminating internal leakage:

Water injection seals the element during compression, improving overall efficiency by eliminating leakage that causes energy losses.

High reliability, long service life, low servicing costs and environmentally responsible operation.

Reliability and low maintenance costs are key investment factors. Water-injected compressors have several design advantages that support long life and low servicing costs:

Simpler design

Water-injected compressors are simpler than dry-running oil-free designs. Fewer complex parts mean a lower risk of failure and easier maintenance.

Fewer bearings and only one rotor:

Fewer bearings, usually SiC, and a single rotor reduce maintenance frequency and increase reliability.

Direct drive without a gearbox:

Without a gearbox, there is no oil in the system to change or maintain, further reducing costs and simplifying operation.

Lower speeds and temperatures:

Lower operating and discharge temperatures and lower speeds improve efficiency, extend compressor life and reduce servicing costs.

Completely OIL-FREE:

Dry-running oil-free compressors contain oil in the gearbox. Water-lubricated compressors contain no oil anywhere, reducing the risk of environmental oil leaks and minimising disposal costs for oil filters and other oily waste.

Specific requirements of water-lubricated compressors

Despite their many benefits, water-lubricated compressors require osmosis-treated water to top up the internal circulation system. Some factories already have suitable water treatment equipment; otherwise, it is installed in the compressor station. This is not complex in terms of investment or operation, but must be included in the design.

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