Selecting the Proper Oil Pump

Pumps, Oil Transfer and Centrifuge Feeding

There are several types of pumps such as centrifugal, gear, vane and diaphragm. Some pumps are well suited for use with oil and others may or may not be. The type and viscosity of the oil also determines which pumps are viable.  Thin oils may be moved faster and thick oils require high torque. Pumps are selected depending upon the application such as oil collection, transfer, blending or centrifuge feed.  Generally, centrifugal pumps are not suited to oil transfer. Centrifugal pumps are high volume-low viscosity pumps that require water thin liquids. Oils are too thick and burn up the motors on centrifugal pumps in a few minutes.

Oil Collection: Because waste oil may have a variety of contaminants such as water, dirt, fish parts and leaves among other things, the best collection method is a vacuum tank. The next best option is a gear pump. Gear pumps are relatively inexpensive, compact and powerful. They transfer oil quickly and reliably. However water is often found at the bottom of waste oil tanks and this is both bad for a gear pump and bad for the oil. When collecting oil with a gear pump, do not pump from the bottom of the waste oil tank, but come up a few inches to minimize water collection.

All but the largest diaphragm pumps are too slow for oil collection. Large diaphragm pumps are both expensive and … large, making them a poor choice for oil collection.

Transfer: Gear pumps are king of oil transfer. They are inexpensive, fast and reliable making them the best choice for quick oil transfer.

Gear Pump Selection: Oil viscosity and transfer rate dictate they size and speed of the gear pump. High speed pumps require thin oils. Low speed-high torque pumps transfer thicker heavier oils. Colder temperatures cause oil to thicken and motor oil is generally regarded as thick especially at 50°F and below. High speed pumps run at 3600 rpm and low speed pumps run at 1800 rpm.

Blending: Gear pumps are good and blending and this is an advantage if you are mixing a batch of oil. Their superior blending ability also creates oil-water emulsions if water and oil are sucked up during oil collection.

Centrifuge Feeding: The best pump for centrifuge feeding is a small pneumatic diaphragm pump. They require minimal air input and the output of these pumps is easily adjusted by varying the air pressure. The output may be shut off with no damage to the pump and it does not require a bypass valve. The diaphragm pump is gentle with the oil and does not “blend” the contaminants into the oil. Nitrile or neoprene diaphragms are used for mineral oils. Viton diaphragms are used for vegetable oils and biodiesel.

Gear pumps are a very poor choice for centrifuge feeding.  Only the very smallest capacity gear pumps match the centrifuge flow. Gear pumps can not be turned down without a bypass valve or variable frequency drive. Electric motors heat up when run much below their rated frequency and gear pumps superior blending ability thoroughly mixes contaminants into the oil making cleaning more difficult.