Gravity Feed Centrifuge Systems

Although there are many centrifuge feed systems, some situations require the simplest feeding system, which is gravity feed. The advantage of the gravity system is that there are no moving parts or pumps. Disadvantages of the gravity system include lower output from variation in flow, variation in cleaning from the changing flow rate and the large height required for consistent flow rate.

Flow rate is affected by height of the feed tank. Oil pressure is about .38 psi for each foot of height. The pressure at the bottom of a full 55 gallon drum is about 1.08 psi. The last 10 gallons in the tank will exert a pressure of about .18 psi. At the 10 gallon mark, flow rate will be about 1/6 of the flow rate when the drum was full.

Turning the tank horizontally improves the situation and lifting a horizontal tank several feet would reduce the variation in feed pressure. A horizontal drum raised 5 feet would see a 26% variation in flow rate and at 8 feet high would see an 18% variation in flow, which is acceptable for general oil cleaning.

Input Pipe Diameter for Gravity Feed Systems

Liquids flowing through a pipe experience frictional losses along the walls of the pipe. Oil flowing through a pipe has a nearly stagnant layer at the internal surface of the pipe that extends inward into the pipe. The thickness of the stagnant layer depends upon the viscosity of the oil. A small diameter pipe may have virtually no effective internal diameter if the oil is thick. Therefore, a large diameter input feed hose is essential for gravity feed systems. A one inch internal diameter hose would not be too large for a gravity feed system, 5/8 inch minimum internal hose diameter may be used with fluid oil and short runs. 3/4 inch ID hose fits over 1/2 inch NPT pipe fittings on the centrifuge heater kit. Thinning the oil by heating will improve the flow properties of the oil, provided the oil does not significantly cool in the hose between the tank and centrifuge.