Teikoku USA Inc. offers a variety of solutions for pumping low flow rates of liquids at relatively high discharge pressures. Before making a recommendation, company Application Engineers will look carefully at these factors: NPSHA criteria, efficiency, horsepower, delivery, and price.
The following hydraulic end designs are recommended for low-flow, high- head applications:
Single and two stage regenerative turbine pumps are offered for flows from 0.5 to 25 GPM and TDH up to 800 ft. at 3450 rpm. Regenerative turbine pumps are designed to optimize head rise at relatively low flow conditions. Regenerative turbine pumps are categorized as low specific speed pumps and offer users better head rise and efficiency when compared to standard centrifugal pumps in similar applications.
Increased efficiency is accomplished by adding energy to the fluid as is passes around the periphery of the turbine wheel. By repeated action of the turbine wheel on the fluid head is added around the entire circumference from the suction nozzle to the discharge. The suction nozzle is designed to minimize head losses of the fluid entering the impeller and features a relatively small low-pressure space as compared to conventional centrifugal pumps. The fluid must be accelerated tom wheel tip speed to fill the inlet chamber and begin adding the regenerative head.
The cut water can be trimmed to reduce the pressure developed by the pump and meet a specified design point.
Teikoku USA Inc and the Chempump division offer a large variety of multi-stage pumps for applications requiring high discharge pressures. Increased heads are achieved by moving the fluid from the discharge of one impeller to the suction of another. Up to 10 impellers can be installed into a single pumping unit, creating heads up to 2,000 feet and flow rates to 450 US GPM using 2-pole (3450 rpm) motors.
Radial Vane pumps are designed to optimize performance at low pump specific speeds, when the application calls for relatively high heads at low flow rates. Improved performance results from the pumps ability to produce up to 50% higher output head for a given impeller diameter due to the straight radial vanes and a fixed diffuser outlet. Smaller impeller diameters translate into reduced motor windage losses and therefore, less wasted horsepower. The diffuser also limits the flow the pump can produce, thereby lowering the maximum input horsepower and permitting a smaller, more efficient motor that will significantly reduce reduced pump cost. Optimized for low flow, the radial vane impeller has excellent NPSHR characteristics.
Radial Vane pumpsâ€™ compact design uses a circular volute, which reduces radial side loads on the pump shaft and bearings when the pump operates at low flow. This combination of low loads and excellent performance makes the Radial Vane pump an ideal candidate for higher rotational speeds such as those produced by a gearbox or variable-speed drive. Output heads of over 1000 ft can easily be accomplished using VFD technology.
The addition of variable speed drives is an excellent and low-cost solution to increase the differential pressure of â€œstandardâ€ centrifugal pumps. The head developed by a pump is increased by the square of the difference of the speed. For example, if the speed is increased by 10%, the discharge pressure is increased by 21%. If the speed is increased by 20%, the discharge pressure is increased by 44%. At the same time, pump flow rates will increase in direct proportion to the increase in speed.
When using variable speed drives, take care not to overload the motor since the horsepower required is directly proportional to the cube of the difference in the speed.
Standard canned motor pumps can operate between 1035 and 4140 RPM without any special considerations as long as the motor is not overloaded at the higher speeds. For speeds above 4140 rpm, special motors and bearing systems are available.