The Diesecraft Centrifuge is a brand name for a pressure driven centrifuge. There are other brands available. A centrifuge will remove particulates that regular filters miss. It also does a good job of removing free. The evidence is in that it also removes some dissolved water. One of the biggest advantages is cost. If you are good at scrounging up used equipment, it can cost you as little as $200 to setup. If you buy everything new, it can cost you as much as $1000.
Centrifuging can reduce the volume of oil you have on your property, by reducing settling time. For example if you cut your settling time from two weeks without a centrifuge to one week with a centrifuge, then you cut the volume of oil being settled in half. The main reason for reducing the volume of oil on hand is safety. Vegetable oil is a fuel and has a high energy content and is a fire accelerant, meaning it will cause fires to rapidly spread.
A centrifuge works by increasing gravity by as much as 2000 times, speeding settling from months to minutes. A pressure driven centrifuge like the Dieselcraft uses oil being ejected through nozzles acting like a rocket to spin the bowl. Dirty oil is introduced into the rotor housing where the particles and free water are forced to quickly settle in the rotor housing. The clean oil ends up falling out the bottom of the centrifuge base.
A centrifuge of any style can remove free water and some emulsified water, like the emulsified water that has been absorbed by food particles suspended in the oil. In addition as they remove the free and emulsified water, they also remove water soluble acids and other water soluble nasties. Another advantage of the pressure driven centrifuge is that can remove some of the dissolved water as well. When it sprays out of the nozzle, it acts like a flash evaporator removing some of the dissolved water. The lower your humidity, the more water it will remove. It seems to speed up the water removal if the oil is heated to about 160°F. Although, according to Sunwizard, who introduced the pressure driven centrifuge to the SVO world, heating is optional.
Heating, when used is accomplished in two ways, an inline heater or a flexible silicone drum heater. Inline heaters are made by screwing a water heater element into a pipe tee. It is usually placed between the pump and the centrifuge. If the oil stops flowing, the element can overheat. Some have addressed this by adding a snap disc or water heater thermostat to prevent overheating. You do not want your oil to go much above 160°F or it can polymerize and gunk up everything. Inline heaters can be done on the cheap, but they also require some mechanical skills to put together without leaks. Silicone drum heaters are stupidly simple to install, but they are expensive and since they are heating all the oil at once, they can take a long time to heat up.
To make it all work, you need a pump capable of supplying enough volume and flow to meet the needs of the centrifuge. Each centrifuge is different, but the DieselCraft OC20 needs a pump that can produce 1 gallon per minute at 100 psi. There are a few pumps that can meet these requirements. The two types of pumps that are commonly used are gear pumps and power steering pumps.
Power steering pumps are vane type pumps with a pulley and mounting brackets on them already. Just hook up an electric motor to power it and there you go.
Gear pumps, like the Teal grease pump, are great for the task. There are even some gear pumps designed to be mounted on TEFC motors using carbonator style motor mounts like the one in this picture.
Both gear pumps and vane pumps need a pressure relief valve to protect the plumbing from destructive high pressures that can happen in the event of a clog blocking the flow. There are gear pumps with internal pressure relief valves which can simplify the plumbing some. Pumps with internal pressure relief valves should be avoided because when they are used to regulate the pressure, they tend to get hot enough to polymerize the oil and cause the pressure relief mechanism to fail. Overheating is not a problem with external pressure relief valves.
Gear pumps are less tolerant of trash than vane pumps and you need a pickup strainer rated for 80 mesh or finer. While they are not required for the vane pumps, it is still a good idea to use a pickup strainer to keep the stuff that can clog the centrifuge out of the piping.
Paul used a washing machine motor to drive his teal pump. He is using an external pressure relief valve with the overflow going back to the input line on the pump. He is dumping into a sock filter as an experiment to see what the sock filter can catch that the centrifuge misses. He has installed a water heater element in the piping between the pump and the centrifuge and is using a water heater thermostat to control the temperature.
After six years, Paul still thinks this system is fantastic. He has found that if he mist washes his oil and let it settle for a week before centrifuging, he can get three to four drums done before having to clean the gunk out of the centrifuge. A gasket blew out of the teal pump so he switched to a power steering pump from a '86-'90 Honda Acura Legend shown on the left. Unlike most power steering pumps, this one is a gear pump. He had to remove the pressure spring from the centrifuge after it got gunked up enough to reduce the flow of oil to a trickle. He also quit using the sock filter after finding out it added nothing to the setup. He did add a final filter, a 2um Caterpillar Filter 1R-0749 (same as Fleetguard FF5319) as a little extra insurance. He says he can get about 1000 gallons through the final filter before it starts plugging.
Below is a video Paul shot of his DieselCraft centrifuge.
Here is my Dieselcraft OC50 centrifuge setup. It does not use heat. It has a carbonator mounted gear pump and motor with built in pressure relief valve. I made the base out of 2x12 pine so that I could roll the drum under the centrifuge. Not shown is the suction line screen mounted on the inside of the drum. I've added a camlock fitting between the pump and the drum so I can separate them. The neat feature is the drain extension. It channels the flow into a single stream to reduce splashing. The picture of the rotor cleaning is for oil heavy with fats and hydrogenated oils. The only change I would make to what's shown is to replace the braided hose between the pump and the centrifuge with a hydraulic line which would hold up better long term to the 90 psi needed to run the centrifuge.
Click on the pictures to enlarge.
How Gear Pumps Work
Spinner II®Trial Results Summary
Spinner II®Trial Full Report
The Frybrid Still - Near the bottom Frybrid explains how to install a centrifuge on the Frybrid Still
Pressure Relief Valve - from Graingers
Sunwizard's website - His Dieselcraft setup
Options for Removing Water in Oil - Machinery Lubrication Magazine