AirDog® Fuel Air Separations Systems for Class 8 trucks for specific engines are complete with mounting brackets, special fuel fittings and air/vapor return lines, when mounted in the location of the original primary fuel filter. Note: The mounting brackets included are for a flat surface, spacers or a flat bracket may need to be fabricated. 

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PureFlow® Technologies, Inc.

5508 Business 50 West

Jefferson City, MO 65109

Toll Free:1.877.GO DIESEL


Direct: 1.573.635.0555

Fax:     1.573.635.0778


Hours of Operation


8:00 AM-4:30 PM

Saturday & Sunday



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How Does Air Become Entrained In Diesel Fuel?


As in all liquids, air becomes entrained in diesel fuel from sloshing and agitation! Air can be on the surface of the fuel in the form of foam or it can be in the bulk fluid in the form of tiny bubbles. Entrained Air is an issue of an "in use" engine in operating equipment!


What is Pump Cavitation?


Pump cavitation, simply put, is the pump not having enough pressure flow, or "Net Positive Pressure Head" of fuel coming into the inlet to completely fill the vacuum chamber of the pump.


Diesel fuel, as is true with all petroleum base liquids, will give off vapor when subjected to a vacuum. The amount of vapor depends upon the level of vacuum and temperature.


How Does Fuel Filter "Restriction" Effect Cavitation?

In the diesel engine industry, "fuel filter restriction" is a term that refers to the vacuum level at the inlet to the transfer or lift pump. It is measured in inches of mercury (in hg).


As the filter plugs with use, it further restricts the flow and increases the vacuum level in the pump.


The amount of vapor produced depends upon the level of vacuum.


What Else Increases Cavitation and Vapor? 


As the fuel levels in the tank(s) goes down as the fuel is burned, the "Dry Suction Lift" increases. This reduces the flow, increasing the vacuum.  


Operating at higher altitudes, where atmospheric pressure is less, reduces the fuel flow and increases vacuum. For example, at Denver,  atmospheric pressure  is about 17% less than at sea level and at Eisenhower Tunnel, it is approximately 32% less. Having less pressure to drive the fuel from the tank to the transfer pump, reduces the flow and increases the vacuum levels.


Higher fuel temperatures cause more vapor to form than cooler fuel under the same vacuum!