Centrifugal and volumetric pumps are powerful devices for handling fluids in complex industrial and urban systems. However, it is important to choose the right equipment for the needs of your facility. This section describes the differences between the two types of pumps, the fluids they can control, and the most common uses for each pump.
Fluid Transfer Mechanisms
Centrifugal and volumetric pumps transport water from inlet to outlet in a controlled manner in terms of strength and volume. However, the mechanisms used are different. Positive displacement pumps draw fluid into a cavity, or displace the fluid, and then force the fluid out of the cavity through suction. Centrifugal, or aerodynamic, pumps have a spinning impeller that draws the fluid into the pump and forces it out of the outlet point at an increased velocity.
Types of Fluid Transferred
positive displacement pumps can handle highly viscous fluids, and their flow rate can increase as the fluid gets thicker. Centrifugal pumps, on the other hand, can’t handle viscous fluids as well because of the frictional losses. Also, positive displacement pumps can handle shear-sensitive fluids—or fluids that change when force, stress, or pressure is applied—whereas centrifugal pumps cannot; the impellers present a risk to the fluid. Positive displacement pumps can also handle intermittently dry periods and can start without being primed by the liquid in the system. Centrifugal pumps need liquid in the unit to kick-start the pressurized control.
The Main Difference between these pumps is several different types of positive displacement and centrifugal pumps, each of which uses slightly different mechanisms and can handle different loads but which still uses the basic concepts of positive displacement and rotational force to cause movement. Facilities should first decide whether a positive displacement or centrifugal pump is the best choice based on pressure and flow rate demands, the type of fluid being moved, and the required suction lift before choosing a specific pump type and model.
Performance of the Pumps
One of the main performance differences between positive displacement and centrifugal pumps is the flow rate. A volumetric pump maintains a constant flow rate even when the pressure changes, whereas the fluid leaving a centrifugal pump changes the flow rate as a function of pressure.
Centrifugal pumps operate at low viscosity levels when pumping fluids. This includes water, oil, fuel, and chemicals. This is the most common type of pump used in high capacity applications requiring low pressure and high flow rates. Some popular applications include:
- Municipal water and water supply systems
- Air conditioners and water circulators
- Petrochemical and light fuel transfer stations
- Cooling towers
- Boiler feeds
With a vortex impeller, centrifugal pumps can even handle some fluids with solids. However, they work best when pumping consistent high-volume quantities of water.
Positive Displacement Pump
Volumetric pumps, on the other hand, are suitable for high pressure and low flow applications with viscous fluids. These pumps work well in the following applications:
- Municipal sewage systems
- Oil processing centers
- Manufacturing centers that produce or process thick pastes and other viscous materials
Complex systems such as food processors and other manufacturing plants benefit from combining the two types of pumps. For example, a food processor needs a centrifugal pump to add water in batches, but a volumetric pump to control the speed of a coarse mixture. Refineries may need positive displacement pumps to process crude oil, but centrifugal pumps can be used to process finer and lighter by-products.