The centrifugal pump is the most common type of pump used for many industrial and commercial fluid transfer applications. There are many different types of centrifugal pumps including circulator, single- and multi-stage end-suction, single- and multi-stage split-case, and vertical in-line pumps.
Two of the most common are end-suction pumps and split-case pumps.
Let’s look at the differences between the two and some of the benefits of each type of pump.
How Centrifugal Pumps Work
Centrifugal pumps work by forcing fluid through one or more rotating impellers. As the fluid moves through the impellers, centrifugal forces increase the velocity and pressure of the fluid.
The fluid meets the impeller at its eye or at the rotating axis. The rotation of the impeller accelerates the fluid, which then flows outward into the pump casing. From the casing, the fluid is then discharged at a controlled pressure.
There are two basic types of centrifugal pump casings: volute and diffuser. Volute casings have an offset impeller, which creates a curved funnel with the area increasing towards the pump outlet or discharge. This helps to increase the fluid pressure towards the outlet.
Diffuser casings have a series of stationary vanes surrounding the rotating impeller. The pressure is increased as the fluid is passed through these vanes. Diffuser casings may not be the best choice for applications involving entrained solids or high viscosity fluids, as the diffuser vanes can add unnecessary constrictions to the flow.
End-suction pumps are designed so that the incoming water enters the pump horizontally through the end. The water then changes direction and is discharged vertically, perpendicular to the line of suction.
End-suction pumps usually feature a volute casing and only one impeller. They are single-suction and can either be close-coupled or flexible-coupled. In a close-coupled pump, the impeller is directly mounted to the motor shaft. A flexible-coupled pump has the impeller and the motor shaft separated by a flexible coupling.
Close-coupled pumps don’t require alignment as the impeller is fixed to the motor shaft. Flexible-coupled pumps, on the other hand, can become misaligned during maintenance and this can create problems for the pumping system.
End-suction pumps are normally driven by an alternating current electric motor, though there are direct current motor driven ones available, as well as pumps driven by air motors, hydraulic motors, steam turbines, and diesel and petrol engines.
End-suction pumps tend to have a lower capacity range than a split-case pump and are generally not recommended for large fluid flow applications.
Split Case Pump
Split-case pumps are flexible-coupled pumps. The assembly, including the motor and pump, is rigidly mounted to a common base-plate. Pump suction and discharge are arranged in the horizontal direction and are perpendicular to the shaft.
Split-case pumps can be either single-suction or double-suction. In a single-suction pump, the water enters the impeller from only one side. For double-suction, the fluid enters the impeller from both sides. Double-suction designs reduce the risk of hydraulic imbalance, which makes double-suction split-case pumps generally preferable to single-suction.
Split-case pumps can also have multiple impellers for multi-stage operation, increasing the available head within a single pump.
These pumps are used mostly in fire protection systems and the HVAC industry for large capacity systems.
Benefits of End-Suction Pumps
End-suction pumps generally have a more compact design than split-case pumps. This makes them good options when space is at a premium and you need a pump with the small footprint.
Because of their simplicity of design, end-suction pumps also tend to have a lower up-front cost than other comparable pumps.
Benefits of Split Case Pumps
While split-case pumps generally have a higher initial cost than end-suction pumps, they require less maintenance and can be expected to have a longer operating life. That means that while it may cost more up front, the savings you can expect from the lower maintenance requirements and reduced downtime will help you recoup that up-front cost.
Split-case pumps are also easier to maintain as the top half of the casing can be removed, exposing the internal components (like bearings, shaft, impellers) without disturbing the suction or discharge piping or moving the motor.
These pumps also tend to be more durable as the pump casing is often heavier and designed to handle higher working pressures, vibrations and thrust forces.