Pumps parallel operation

Here we see something interesting. Recause the system is designed for both pumps running in parallel, when only one pump is operating, this pump will run to the right of its REP. This situation brings it s own peculiar set of implications, not often understood in indu.stry. 

Pumps are operated in parallel to divide the load between two (or more) smaller pumps rather than a single large one, or to provide additional capacity in a system on short nodce, or for many other related reasons. Figure 3-35 illustrates the operational curve of two identical pumps in parallel, each pump handling one half the capacity at the system head conditions. In the parallel arrangement of two or more pumps of the same or different characteristic curves, the capacities of each pump are added, at the head of the system, to obtain the delivery flow of the pump system. Each pump does not have to carry the same How but it will operate on its own characteristic curve, and must deliver the required head. At a common tie point on the discharge of all the pumps, the head will be the same for each pump, regardless of its flow. 

Figure 32.46 demonstrates how variable-speed drives will give a wide range of flows. Systems supplied by positive displacement pumps do not usually need wide flow ranges, but the same principle of parallel operation will apply. 

The piping and valves may be arranged to enable two centrifugal pumps to be operated either in series or in parallel. For two identical pumps, series operation gives a total head of 2Ah at a capacity Q and parallel operation gives a capacity of 2Q at a total head Ah. The efficiency of either the series or parallel combination is practically the same as for a single pump. 

Pumps that have stable head/capadty curves (continuous head rise to shutoff) are preferred for all apphcations and are required when parallel operation is specified. When parallel operation is specified, the head rise shall be at least 10 percent of the head at rated capacity. If a discharge orifice is used as a means of providing a continuous rise to shutoff, this use shall be stated in the proposal. 

When needed, greater head or greater capacity may be obtained by operating several pumps in series or parallel. In parallel operation, each pump develops the same head (equal to the system head), and the flow is the sum of the flows that each pump delivers at the common head. In series operation, each pump has the same... 

The components of a thermoelectric cooler are indicated by the cross section of a typical unit shown in Fig. 1. Therm oelectiic coolers such as this are actually small heat pumps that operate on the physical principles well established over a century ago. Semiconductor materials with dissimilar characteristics are connected electrically in senes and thermally in parallel, so that two junctions are created. The semiconductor materials are n- and /i-type and are so named because either they have more electrons than necessary to complete a perfect molecular lattice structure (ri-type), or not enough electrons to complete a lattice structure (/7-type). The extra electrons in the -type material and the holes left in the /7-type material are called carriers and they are the agents that move the heat energy from the cold to the hot junction. 

If two pumps with head-discharge characteristics plotted in Figure 4.10 (dashed lines) are to be used, (a) determine the pumping system discharges when each pump is operated separately and, when both pumps are operated in parallel (b), determine at what head will both pumps operated in series deliver a discharge of 0.2 mVs. 

When only pump no. 2 is operating, the system discharge is 0.31 mVs. Ans When both are operated in parallel, the effective characteristic curve for pump no. 1 is shifted horizontally to the right until the top end of the curve coincides with a portion of the effective curve of pump no. 2, as shown. This has the effect of adding the discharges for parallel operation. As indicated, when both are operated in parallel, the system discharge is 0.404 mVs. Ans... 

Another way to speed up HPLC that does not interfere with the existing gradient separation method is by parallel operation of several HPLC columns. The development in this direction started a couple of years ago when fast gradient separation was first combined with mass spectrometry-based detection. Parallel column operation was achieved by a single pumping system and a splitter tee that transferred the gradient flow onto two HPLC columns. The effluent of the two columns was simultaneously sprayed into a modified ion spray interface of a quadrupole mass spec-trometer. From the overlay chromatogram both desired and previously known compounds were identified after their molecular ions were filtered from the total ion current (TIC). In this first system, however, it was difficult to enhance the parallelization, and the detection system created a bottleneck. ... 

When only one pump is used for parallel operation of several HPLC columns, it is almost impossible to get the same flow conditions in the individual branches, even if the columns are taken from the same manufacturing lot. This is because of the variation in backpressure of the individual columns, and it becomes even more predominant in a gradient run and can dramatically change over the lifetime of a column. 

Pumps suitable for this service should be capable of parallel operation, and should deliver water against a head of about 350 feet. (150 psi). Because of the corrosive natmre of the circulating water and the high velocities in the pumps it is recommended that they be made of stainless steel, unless corrosion... 

Thermoelectric (TE) modules are solid-state heat pumps that operate on the Peltier effect [1]. A TE module consists of an array of p- and n- type semiconductor elements heavily doped with electrical carriers. The array of elements is soldered so that it is electrically connected in series and thermally connected in parallel [1 ]. This array is then often affixed to two ceramic substrates (insulators), one on each side of the elements as seen in Figure 1. 

Krishnadasan et al. [108] reported the use of a microfluidic reactor to carry out the synthesis of CdSe nanocrystals along with an inline spectrometer to monitor the emission spectra. CdO and Se were pumped into the two inlets of a heated Y-shaped microfluidic reactor. The emission data are fed into a control algorithm that reduces each spectrum to a scalar dissatisfaction coeflEcient. The reaction conditions including CdO and Se reactant flow rates and temperature are adjusted in an effort to minimize this coefficient for an optimum processing condition. Toyota et al. [109] reported a combinatorial synthesis system for CdSe nanocrystals using parallel operation of microreactors combined with an online detector. A multifaceted assessment of reaction parameters was made to achieve optimum control over size, size distribution, yield, and photoluminescence of CdSe nanocrystals (Figure 7.21). 

Two identical centrifugal pumps are operating in parallel and serving a single distribution loop. Which of the following will occur if one of the pumps is deenergized ... 

Be aware that in some cases, you ll have to live with cavitation. Many pumps suffer cavitation for reasons of inadequate design, hor example, when operating only one pump in a parallel system, this pump tends to go into cavitation. Pumps that perform more than one dut through a valve manifold tend to suffer cavitation. Pumps that fill and drain tanks from the bottom tend to suffer cavitation. The last pump drawing on a suction header tends to cavitate. And of course vacuum pumps and pumps in a high suction lift arc candidates for cavitation. 

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