Month: April 2017

How do You Compare Centrifuges, by RPM or RCF?


Although a centrifuge is not particularly difficult to build, a good centrifuge requires good engineering. There are several centrifuge manufacturers out there offering their products by RPM and a few manufacturers specifying G force. So what really matters and how do you compare centrifuges?

What is RPM?  Revolutions Per Minute

What is RCF? RCF Relative Centrifugal Force or G force. How many times the force of gravity.

Since a centrifuge is a “high gravity” settling machine, knowing the G force is important.

G force is the actual power of the centrifuge, similar to horsepower of a motor.

US Filtermaxx 10,000 G Force Centrifuge

You specify a motor by horsepower not RPM, for example, “My Dodge Charger has a 372 horse power motor,” not “My Dodge Charger has a 4500 RPM motor.”

RPM has little to do with actual power output in an engine or a centrifuge.  The COX gas engine in my model airplane ran at 17,000 RPM and produced .08 horsepower.

A stationary Diesel operates between 60 and 200 RPM and may produce over 100,000 horsepower.

Similarly, actual centrifuge power is not rated by RPM, but by G force.  For example, 1200 Gs is 1200 times the force of gravity.   3000 G is 3000 times the force of gravity. Now you have a way to compare the power of a centrifuge.

If a manufacturer doesn’t quote the G force, then they either don’t want you to know what it is, or they don’t know how to calculate it. Either way, you have no idea what you are buying if you don’t know the G force of the centrifuge. A properly engineered centrifuge starts with specifying the required G fouuuuurce, and then the machine is designed to meet the stresses produced at that G force. Building a centrifuge with no idea of the stresses produced when running at speed is like designing brakes on a car with no idea of the force required to stop.

Summarily, one should be skeptical of manufacturers offering centrifuges without specifying their G force.  How much engineering could be involved in a piece of machinery where the maker only knows how fast it goes?  Look under the hood. You wouldn’t buy a Corvette with a 4 cylinder engine. When shopping for a centrifuge, ask for the G force so that you can properly compare units.

cylinder centrifuge
USFiltermaxx 17,000 G Force Tubular Centrifuge





One Pass #Oil Cleaning and the Automatic #Centrifuge Controller

Our tests show that #wastemotoroil (WMO), typically contains between 3 to 5 percent solids. When cleaning #WMO, the solid particulates become concentrated next to the bowl wall and clean oil floats to the center of the bowl, spilling over the top edge and going out of the centrifuge through the clean oil output port.  As the solid particles move to the bowl wall, some of the solid matter sticks to the sides of the bowl;Solid Particulates in Used Motor oil. however, much of it is concentrated as a slurry of solid particulates in oil. If you feed the WMO, or oil, slow enough for long enough time so that all the particulates move to the wall, you could remove all the particulates as solid matter stuck to the sides of the bowl. However, such a slow feed rate and the amount of time spent scraping solid matter from the centrifuge bowl are too impractical and labor intensive for actual production.  Much of the solid matter can be removed before the bowl fills up. Draining the slurry from the centrifuge before the bowl fills up allows a higher feed rate without sludge spilling over into the cleaned oil. This greatly extends the run time between bowl cleanings and also reduces or eliminates the sludge that spills into the cleaned oil.

The amount of WMO sludge concentrated in the centrifuge bowl depends upon:

1. The #Gforce, with higher G force having a higher rate of concentration

2. The feed rate, which must be low enough for the centrifuge to do its job and settle the sludge to the outer wall (again, higher G force = faster and higher concentration of #sludge).

At some point, the bowl will fill with sludge and spill over into the cleaned oil. At this point, the centrifuge is removing very little if any #contaminants as they spill over into the cleaned oil as fast as they are removed. Two remedies for this situation are:

1. Slow the feed rate so low that all the particulates move to the outer wall and only cleaned oil is discharged, but we have already seen that this is impractical.

2. Stop the centrifuge and drain the sludge before it spills over, contaminating the cleaned oil.

The size of the bowl dictates the volume of oil processed between draining.

How often should the centrifuge be stopped and the bowl drained? An approximate starting point is determined by the bowl size. The #USFiltermaxx #WMO centrifuge has about 165 cubic inches sludge capacity.

5% =.05

3%= .03

1 gallon = 231 cubic inches

165 cubic inches / .05 = 3300 cubic inches of oil

3300 cubic inches / 231 in3/gal = 14.3 gallons

165 cubic inches / .03 = 5500 cubic inches

5500 cubic inches / 231 in3/gal = 24 gallons

So the optimal range of oil fed to the US Filtermaxx centrifuge between bowl draining is between 14 and 24 gallons. Running any centrifuge longer at the bowl capacity is like trying to put 10 gallons of sludge in a 5 gallon bucket.

Run time between draining will vary by G force, #viscosity of the oil and percent #contamination, however; volume between draining will remain about the same.

The volume between draining for other sized bowls is calculated in a similar manner.

A centrifuge bowl capacity of 1 pint = 28.875 cubic inches

28.875 / .05 = 577 cubic inches

577cubic inches / 231in3/gal = 2.5 gallons

For a bowl capacity of 1 quart = 5 gallons

Nobody wants to sit around and wait to drain their centrifuge bowl, so here at USFiltermaxx, we design a variety of programmable automatic centrifuge controllers to remove the burden of manually draining the sludge from the centrifuge, allowing #automatic one pass cleaning.


US Filtermaxx Dual Centrifuge Controller

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