Differences Between Rotary & Centrifugal Pumps

• The key difference between rotary and centrifugal pumps is the kind of energy they use. Rotary pumps use mechanical energy to pump liquid; centrifugal pumps use kinetic energy, which is the energy that comes from movement. This means that each type of pump has different strengths and weaknesses, depending on the amount and type of liquid in question.

Efficiency

• Rotary pumps are generally considered more efficient than centrifugal pumps. Pump efficiency depends on the proportion of liquid that passes through the pump -- the less water to backwash in the pump, the less efficient the pump, and vice versa. Rotary pumps use mechanical energy; they function by increasing then decreasing the liquid's volume, thus encouraging it to move into the lower-pressure area as the volume decreases. To visualize this, think of a plastic bag with a hole in it -- if you squeeze the bag, you are reducing the water's volume and increasing the level at which the water goes out of the hole. When you stop squeezing, the water just slows down -- it doesn't go backwards.

Volume

• Centrifugal pumps, on the other hand, are better for high-volume pumping where efficiency is not as high of a priority. This is because they function on kinetic (movement) energy rather than mechanical energy. A centrifugal pump operates with an impeller. The impeller spins, which makes liquid spin around it. The effect is that the liquid on the outside edge of the circle gains more energy than the liquid on the inside edge, as it is moving faster. This makes the centrifugal pump ideal for moving large amounts of easy-to-move liquid, such as water.

Viscosity and Pressure

• Viscosity and pressure are closely related -- a more viscous liquid, such as oil or melted cheese, is more pressurized than a less-viscous liquid like water. Rotary pumps are ideal for high viscosity liquids because they can increase pressure more effectively than centrifugal pumps. Since centrifugal pumps rely on the liquid's ability to energize itself, they are less than ideal than rotary pumps for more viscous liquids, which use their own energy to move.