The Basics

There are almost as many different engine models on the market today as there are applications. In many of these applications, engines must function in environments, which can be hazardous to optimum operation.

Although dirt can enter an engine from different sources, the most common path of entry is through the air intake system. Research shows that airborne dirt particles ranging in size from 10 to 100 microns cause the most engine damage. One micron equal 0.000039ths of an inch. The most harmful particles in this range are the silicates. Silicates are a major component of sand. At normal engine operating temperatures, silicates (sand) in the cylinders will crystallize to a diamond-like hardness.

0.0001 microns Smog
0.001 microns Metallurgical dust and fumes
1.0 microns Clouds, Clay
10 microns Fog, silt, fly ash, fertilizer, insecticide dust, ground talc
100 microns Mist, fine sand, coal & cement dust, milled flour
1,000 microns Drizzle, coarse sand
10,000 microns Rain, gravel, beach sand

Studies show it only takes an average of eight (8) ounces of dirt to ruin an engine. Problems caused by even a small amount of dirt getting past the filtration systems include premature wear of bearings, rings, and cylinder surfaces. This results in excessive oil consumption when worn cylinder walls and rings allow lubricant into the combustion chamber.


A precleaner is a better, more effective way to extend air filter life. There are three types currently available. These are the collector (dust) bowl, aspirated, and atmosphere discharge types. All operate on the principle of centrifugal force. The method of dirt removal for each type of precleaner will be reviewed in detail as follows:


This precleaner is a clear plastic, collection bowl type; it is sometimes referred to as a dust bowl precleaner. Air is drawn up through the bottom, over angled vanes, causing the air to spin. The dirt follows the inner wall up and over the edge into the collection bowl while the clean air enters the intake pipe.

Problems can include:

  1. The need for frequent cleaning of the collection cup, especially when moisture turns the dirt into mud.
  2. The collection bowl becomes cracked, scratched, and cloudy over time, making visual inspection nearly impossible.
  3. The unit must only be mounted vertically.
  4. Some of the dirt from the collection cup can be drawn down into the filter element when the engine is throttled down or shut off.
  5. This precleaner is only efficient within a limited range of particle sizes.


The aspirated style precleaner consists of two major sections, the precleaner and venturi.

The precleaner section centrifugally separates contaminate which is directed to a low-pressure area. The venturi section located in or on the exhaust. This creates a vacuum to carry away contaminates which are then discharged into the atmosphere.

This is a fairly efficient type of precleaner when it is new, but in time some significant problems can be encountered, including:

  1. Moisture mixing with the dirt clogs the ports or vacuum tubing.
  2. Fresh air carried over into the exhaust stack via the vacuum tubing can cause re-ignition of unspent fuel, causing a rapid “burn out” situation in the muffler or exhaust stack.
  3. Restriction caused by the venturi can create backpressure resulting in an engine running hotter and less efficiently.


Incoming air is drawn in past louvered openings, which rotate the internal, free spinning impeller. The centrifugal force caused by the spinning impeller separates the dirt, dust, moisture, and other particulate from the air. The cleaned air then enters the intake stack while the dirt is expelled, through a louver, back into the atmosphere.

Problems can include:

  1. The need to vertically mount bottom discharge units to achieve efficient discharge of dirt and moisture.
  2. Cracking or shattering of plastic units or components.
  3. Rusting and corrosion of carbon steel constructed units.

Precleaners cannot completely eliminate air filters; they do however vastly extend filter life. Also precleaner use can help with lower fuel consumption, reduced maintenance and extended time between overhauls.



Why is CENTRI® the best?

The CENTRI® by DRM Diversafab Corp. is designed with the air-flow-through principle featuring:

  • Eight (8) different CENTRI® models to cover your clean air requirements from 50 to 1600 CFM
  • Heavy duty, non-rusting aluminum and stainless steel construction, yet lightweight, requiring no additional clamps or supports.
  • Self-cleaning, maintenance free design.
  • Curved and angled vanes to direct the air flow to maximize cleaning efficiency.
  • Stamped one-piece stainless steel impeller is precisely balanced, eliminating vibration, noise, and premature bearing failure.
  • Easy installation features allow for mounting the CENTRI® Precleaner in any position, including inverted.


For all engines, the C.F.M. can be determined by using the formula below:
(NOTE: C.I.D = Cubic Inch Displacement; R.P.M = Revolutions Per Minute; Vol. Eff = Volume Efficiency )



C.F.M. = C.I.D. x R.P.M. x Vol. Eff.
(divided by) 3456


Diesel Naturally Aspirated = .85
  Turbocharged = 1.60
  Turbocharged – Aftercooled = 1.85
Gasoline Up to 2500 RPM = .80
  2500 – 3000 RPM = .75
  3000 – 4000 RPM = .70


C.F.M. = C.I.D. x R.P.M. x Vol. Eff.
(divided by) 1728


Diesel Blower-Scavenged = 1.40
  Turbocharged = 1.90
  Turbocharged – Innercooled = 2.10
Gasoline Up to 2500 RPM = .85
  2500 – 3000 RPM = .80
  3000 to 4000 RPM = .75

To convert Metric Displacements to C.I.D. for use in the formulas, use the following conversion factors:

    • Displacement in Cubic Centimeters (cm3) x 0.06102 = C.I.D.


  • Displacement in Liters x 61.02 = C.I.D.

NOTE: Engines equipped with twin air intake pipes, divide the engine C.F.M. by two and apply the proper CENTRI® Precleaner to each of the pipes.



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