Building reliable high-pressure pumps
Basic hydraulic theory tells us that there are three factors that determine the total developed head of a centrifugal pump:
- Impeller diameter;
- Impeller rotation speed; and
- The number of impeller stages.
(Developed head also depends on the density of the pumped fluid, but since this is usually defined by the application, it isn’t really something that can be changed in order to meet a design target.)
Increasing the impeller diameter can increase the head developed by a pump, but it will also increase the overall size of the pump so that there are practical limits to this approach. Increasing rotational speed can also increase developed head, but here again, there are practical limits. Ultra-high-speed pumps can suffer from reliability and durability problems because of the extra strain the high rotational speed puts on bearings and seals.
Multi-stage pumps have emerged as the most practical solution for situations where high pressures are required. Of course adding more stages increases the mechanical complexity of these machines. However, this opens the door to a great deal of design flexibility. The number of stages can be chosen to match the developed head requirements, with more stages added to supply higher output heads (For ring-section pumps, including most of KSB’s high-pressure products, the number of stages built into a pump can be varied, depending on the required duty point of the machine.) For multi-stage pump designs it is also straightforward to tap into the pump at an intermediate stage in order to produce a partial flow of fluid at a pressure below the full output pressure at the final stage. Impellers at each stage can be individually optimized to deliver maximum efficiency. Multi-stage pumps can be designed to be very compact relative to their power ratings with short, stiff drive-shafts and generous bearings.
A gallery of high-pressure pumps
KSB’s HGC family is an excellent example of high-capacity, high-performance multi-stage pumps for boiler-feed duties in power stations and in other large-scale industrial applications.
These pumps are available with delivered heads as high as 4200 metres and capacities of up to 1,450 cubic metres per hour. They can handle fluid temperatures as high as 200°C. The design has been optimized to ensure long, trouble-free service life and simplified maintenance procedures.
HGC pumps have been used effectively in the Alberta oilsands to provide high-pressure water for the in-situ extraction of bitumen from underground deposits.
KSB’s HGM series pumps are smaller than the big HGC boiler feed pumps, with rated heads of up to 1,400 metres and capacities as high as 274 m3/hr.
The development team at KSB Pumps responsible for the HGM pump family looked at every stage of a boiler pump’s life cycle to minimize the cost of installing, operating and maintaining these machines. KSB’s engineers came up with an extremely compact design, which makes it simpler to lay out piping for efficient flows and easy access. Uniquely for pumps in this class the HGM’s bearings are lubricated directly by the water running through the pump. No supply lines, oil pumps or other equipment usually associated with lube oil systems are needed. This reduces both installation and maintenance costs – even to the extent of eliminating the cost of disposing waste oil! The combination of short shafts and closely spaced, medium-lubricated bearings results in very smooth-running, quiet pumps with long service intervals. HGM pumps also feature an axial intake layout and suction impeller, which combine to provide low NPSH (net positive suction head) levels.
HGM pumps are used to provide feedwater for power plants and industrial boilers. They have also been used in the Alberta oilsands to provide feedwater for the steam flood heaters used to generate high-pressure steam for bitumen extraction.
Based on a multistage centrifugal ring-section design, the Multitec family is available in six sizes, with discharge nozzle diameters from 32mm to 150mm. By varying impeller size and the number of stages, KSB engineers can deliver 15 different hydraulic configurations so that system designers can select a pump with the optimum rating for their application. (The smallest member of the family has a maximum capacity of 29 m3/hr, while the largest sets can deliver up to 850 m3/hr.) But, scalability isn’t the end of the versatility story. KSB Multitec pumps are available with casings and hydraulic elements made from a variety of materials, including cast iron, bronze, cast steel and high-strength, corrosion-resistant CrNiMo steel alloys. A number of seal configurations are available, with or without cooling, so that the pumps can be used for a wide range of liquids (water, salt water, solvents, lubricants and fuels) and at temperatures up to 200°C. Multitec pumps also offer the designer lots of flexibility when it comes to system layout: vertical or horizontal mounting options are available for most sizes of pumps, as are a variety of nozzle configurations.
Multitec pumps are used in applications areas as diverse as municipal water supply and wastewater treatment, industrial processes, boiler feed, irrigation, firefighting, reverse osmosis and beyond.
Geared to the general market, the Movitec vertical multi-stage pumps come equipped with 60 Hz high-efficiency motors. Available off-the-shelf, the Movitec series features optimized hydraulic systems, making them the most efficient high-pressure in-line pumps on the market. A range of material and seal options make these pumps highly versatile.
Applications range from fluid transfer to instant pressure boost. With seal available variants rated for temperatures from -30 °C to +140 °C, these standardized centrifugal pumps can handle a huge variety of media, ranging from water (including acidic and alkaline solutions), alcohol, and vegetable oils to petroleum products and condensates, liquid CO2 and LPG. A new addition to the product range is the tri-clamp coupling, the connection of choice for pharmaceutical and hygienic food and beverage applications. These pumps come in nine different sizes (up to 90 mm pipe diameter). Inlet and outlet nozzles are same size and arranged along a common axis to simplify the installation of these pumps piping systems. Movitec pumps are designed to be easy to service; when equipped with Easy Access or cartridge seals, seal replacement can be done without removing the motor.