Form Follows Function: An Introduction to Pump Configurations and Uses
A glance at a pump manufacturer’s catalog or at the American Petroleum Institute’s standard API-610, reveals that hydraulic pumps come in a wide variety of shapes and sizes. In this article, we will describe some of the more common pump configurations and explain how these particular layouts are designed to meet different operational requirements.
Water Transport Workhorses
Water transport duties in municipal or industrial water supply systems typically require the pumping of very large volumes of water on a more-or-less continuous basis. Large water transport pumps can be large consumers of electric power, so high efficiency is important for controlling operating costs. Reliability is also critical since dependable water supply is usually of extreme importance.
KSB’s RDLO and Omega pumps are ideally suited for water transport duties. These pumps, which are available with capacities up to 10,000 m3/h and heads as high as 240 m, feature a single-stage split volute casing design with a centrally mounted impeller supported by bearings on both ends of the drive shaft. This configuration is referred to in the API-610 standard as a BB1 type pump.
There are a number of features that make this type of pump good candidates for water transport applications:
- They can deliver high efficiency over the design operating range. Impellers are optimized for the smooth and efficient hydraulic performance and can be trimmed to fine-tune flow rates to match application requirements. The split casing design means that the inner surface of the casing is fully accessible so that the manufacturer can ensure that the surface finish is very smooth, again for optimal hydraulic performance.
- The impeller is double-sided, with vanes on both sides of its centre line. The casing is similarly symmetrical, with intake flows entering from two sides. This symmetrical layout means that there are no net axial forces on the drive shaft and no need for thrust bearings or pressure balancing disks.
- While the drive shaft is supported by bearings at both ends, only one end exits the casing, so that only one end requires seals. These seals are readily accessible for service, which contributes to lower maintenance costs.
Wastewater treatment adds another set of requirements for pumps. Because wastewater will often contain a variety of suspended solids, including abrasive grit and blockage-creating fibrous materials, special features are often called for. In particular, pumps used in wastewater systems should be easy to disassemble in the field to clear blockages and to replace worn parts.
Submersible pumps, such as the KSB’s Amarex family are often used in wastewater or stormwater management facilities. They consist of a pump that is close-coupled to a motor that is enclosed in a water-proof housing. They are typically installed near the bottom of a well or tank where they draw water directly into their intake. When in position, their output nozzle feeds directly into a pipe that carries the water to the next stage of the facility. If a blockage occurs or maintenance is required, the pump-motor assembly can be hoisted to the surface for clearing or servicing. Submersible pumps are available in a wide range of sizes, with flow rates that range from a few litres per minute to over 10,000 cubic metres per hour. Characteristics of a good submersible pump include:
- A simple, rugged design with long-lasting bearings and seals
- The availability of several types of impellers that can effectively handle different types of material or gas in the water stream
- Effective sealing around the motor, especially in areas like the cable entry, where leaks can damage the motor
Dry Well Pumps: KSB’s Sewatec and KWP pumps are specifically designed for use in wastewater treatment facilities. In dry well installations, the pump and motor are mounted in the open air, with water entering and exiting through pipes. These models feature dependable, long-lasting seals and bearings. Both are available with a selection of special anti-clogging impeller designs. Sewatec and KWP pumps, which are API type OH2 pumps, feature a rear pull-out design that makes it possible to remove the impeller, drive shaft, seals and bearings for service without having to remove the volute casing from its mounts or pipe connections.
High Pressure Specialists
Large high-pressure pumps are used in applications such as power plant boiler feedwater supply or reverse-osmosis desalination systems. Smaller systems, including industrial pressure washers, firefighting equipment and snow-making equipment also need high pressure pumps. The best way to achieve high output pressures is to use multi-stage pumps.
KSB’s radially-split multi-stage pumps ae very well suited to high-pressure applications. Examples include the HGM and Multitec families of pumps. For this type of pump (also known as ring-section or API BB4 pumps) the casings and impellers that make up the stages are “stacked” along the length of the shaft. This is a highly effective design since the size and number of stages can easily be chosen to closely match each application’s requirements. Each component is highly accessible prior to assembly so that dimensional tolerances surface finishes can be closely controlled during manufacture. The result is durable, reliable and highly efficient units.
Low-Head Water Movers
Some water transport applications such as irrigation systems, flood control and intake systems for cooling water require large volumes of water at relatively low heads (5 – 20 metres). Vertical turbine pumps are sometimes used in these situations. While less energy efficient than most volute casing centrifugal pumps, vertical turbine pumps can be straightforward to locate in structures since they are typically located in a vertical tube, with their intake immersed in the reservoir from which they are intended to draw water.
KSB supplies two main varieties of vertical turbine pumps. The Amacan series (pictured here) features a submersible motor that is closely coupled to the impeller. These models are designed to be installed at the bottom of a cylindrical well or chamber. Water is drawn from a reservoir beneath the well, travels upward around the motor and is discharged at the top of the well. The submersible design means that the entire pump unit can be lifted out of the well for clearing or maintenance.
The other type of vertical turbine pump supplied by KSB is the vertical casing design. Here, the impeller is located at the bottom of the pump and is connected to the motor by a long driveshaft. Water is drawn in at the bottom of the casing and discharged though a nozzle near the top. The motor is mounted on a platform at the very top of the structure, where is remains dry and accessible. These pumps are generally large and the casing – a steel tube – is often installed permanently in the facility’s structure.
Inline pumps, such as KSB’s Movitec series, are designed to be conveniently installed in a piping system. They are used to provide pressure boost for a wide range of applications, including pressure washing systems, cooling water supply, firefighting and sprinkler systems, HVAC, building services and many others.
Movitec pumps have a modular design that makes them straightforward to maintain, since seals and bearings can be replaced quickly. They are available in sizes up to 90 mm (pipe diameters) and ca deliver flow rates of up to 113 m3/h.