Adjustable-Speed Pumps

Following the invention of the hydrauHc press in 1795 (3), the use of hydrauHcs expanded rapidly during the nineteenth century. The weight-loaded accumulator, invented ca 1850, was used to store energy in hydrauHc systems. The elementary press circuit has several parts that are common to all hydrauHc systems a reservoir, a pump, piping, control valves, a motor, which in this case is a hydrauHc cylinder or ram, and the hydrauHc fluid. By ca 1860 hydrauHc presses were used for forging, and an adjustable-speed hydrauHc transmission was perfected in 1906 (2). The manufacture of hydrauHcahy actuated machines attained industrial importance after 1920. 

The process controller is the master of the process-control system. It accepts a set point and other inputs and generates an output or outputs that it computes from a rule or set of rules that are part of its internal configuration. The controller output seiwes as an input to another controller or, more often, as an input to a final control element. The final control element is the device that affects the flow in the piping system of the process. The final control element seiwes as an interface between the process controller and the process. Control valves and adjustable speed pumps are the principal types discussed. 

The centrifugal pump directly driven by a variable-speed electric motor is the most commonly used hardware comoination for adjustable speed pumping. The motor is operated by an electronic-motor speed controller whose function is to generate the voltage or current waveform required by the motor to make the speed of the motor track the input command input signal from the process controller. 

The most popiilar form of motor speed control for adjustable-speed pumping is the voltage-controlled pulse-width-modulated (PWM) frequency synthesizer and AC squirrel-cage induction motor combination. The flexibility of apphcation of the PWM motor drive and its 90 percent- - electric efficiency along with the proven ruggedness of the traditional AC induction motor makes this combination popular. 

From a dynamic-response standpoint, the adjustable speed pump has a dynamic characteristic that is more suitable in process-control apphcations than those characteristics of control valves. The small amphtude response of an adjustable speed pump does not contain the dead baud or the dead time commonly found in the small amphtude response of the control valve. Nonhnearities associated with frictions in the valve and discontinuities in the pneumatic portion of the control-valve instrumentation are not present with electronic... 

FIG. 8-85 Pressure, flow, and power for a throttling process using (1) a control valve and a constant speed pump and (2) an adjustable speed pump. 

Adjustable speed motor driven feedwater pumps and high-capacity control rod drive pumps with backup power improve the safety margin by improving correct operator response to non-routine events. 

The cost premium for a motor equipped with speed control can be substantial, sometimes costing twice that of a single-speed motor. But the energy savings from speed control can be substantial, especially for fan and pump systems. Electronic adjustable speed drives continue to become more attractive because the costs of microelectronics and power electronics technologies continue to fall as performance and energy efficiency improve. 

Adjunct mash, 3 574, 577 Adjuncts, brewing with, 70 291-292 Adjustable speed pumps, 20 686-687 Adjuvants, 9 49... 

An adjustable governor capable of regulating engine speed within a range of 10% between shut-off and maximum load conditions it should maintain pump rated speed at maximum pump load. 

Flow control via pump speed adjustment is less common than the use of throttling with valves, because most AC electric motors are constant-speed devices. If a turbine drive is used, speed control is even more convenient. However the advent of the pulse-width modulated (PWM) adjustable speed drive with sensorless flux-vector control has brought adjustable speed (AS) pumping into the mainstream of everyday applications. 

The adjustable-speed centrifugal pump optimization techniques will reduce the energy consumption of pumping stations by 12% or more, depending on the nature of the load served. They will also reduce pump wear commensurately. Combined with surge-free pump starts and stops, and with their inherent predictive maintenance capability, these strategies can also improve the overall plant operation. 

Most biochemical reactions are carried out at defined temperatures. Various kinds of apparatus are used for thermostatting reactions, depending on the temperature and the size of vessels employed (Figure 2-5). The standard form of thermostat for reaction vessels can either be at fixed temperature (e.g., 25 °C, 30 °C, 37 °C, 56 °C, or 95 °C) or may be adjustable. Heated water baths, suitable for beakers, conical flasks and other glass vessels, can be static or shaking, and usually have adjustable speeds. Cryostats must be used for temperatures below ambient these are usually equipped with recirculating pumps which enable, for example, the cuvette holders of spectrophotometers to be cooled. Experiments can be carried out at 0 °C simply by using... 

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