Oil Water Separator

Oil and water separators are unusual on most vehicles. Diesel engines often have a water separator on the fuel line, but any water separator for oil on either gasoline or diesel engines will be something that's added after market.

Some heavy-duty engines and applications have a need for this and shops will install them.

The most common use for an oil/water separator will be in air tools in the shop or to separate petroleum residues from wash water in parts and vehicle washers.

There are three major types of oil-water separators on the market.

Centrifugal Separators

For air tool and similar high pressure applications, the centrifugal separator is the most common (pictured). These are simple filters that plug into the air line and use the fast movement of the air to create turbulence that causes the air to "spin" through the filter, pushing the heavier oils along the edges of the filter housing to be collected in a chamber. The air continues through to power the tools.

These filters increase the longevity of most air tools. Some tools require them in order to maintain their precision operation.

Float Tank Separators

These are simple tanks into which contaminated water is pumped. The water will come in at a mid point in the tank and fill it. The oils will naturally rise to the top of the tank, where they'll "float off" into another chamber for this purpose. The sediments and heavier oils bound to them will sink to the bottom where they can be collected later while the clean water will flow through a pipe out of the chamber.

These are used in low-pressure applications where time and space are not a consideration. Many vehicle wash bays, simple parts washers, and the like will use this type of separation to remove petroleum from gray water.

Micro Filter Separators

These are filters made of fiber, paper, or other materials that filter down to the micron or sub-micron level. They physically remove the oil by forcing water through the filters and capturing the oil molecules as they pass through.

Since petroleum products are generally of larger molecules than water (with the exception of petroleum gasses), they can be trapped in this way. These are common in vehicle applications where oil-water separation is needed.