Pumps in series

Sometimes it is advantageous or economical to use two or more pumps in series (one pump into and through the other) to reach the desired discharge pressure. In this situation the capacity is limited by die smaller capacity of any one of the pumps (if they are different) at its speed of operation. The total discharge pressure of the last pump is 

Applied Process Design for Chemical and Petrochemical Plants 

INNER SEAL X OUTER SEAL PUMP SEAL HOUSING 

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Figure 3-35. Operation curves of two duplicate centrifugal pumps in series and parailel.

Figure 32.45 (a) Pumps in series and parallel (b) three identical pumps running in parallel... 

A cryogenist does not usually need a general purpose mass spectrometer, but the cryogenist cannot work without an LD which is made up of a small vacuum system (rotary pump or diaphragm pump in series with a turbo pump) and a mass spectrometer for the detection of light gases (H2,3He and 4He). 

Consider two centrifugal pumps in series as shown in Figure 4.10. The total head for the pump combination AhT is the sum of the total heads for the two pumps, ie... 

The operating characteristics for two pumps in series are obtained as follows. 

Compare AhT from Step 3 with Ah, from Step 2. If they are not equal repeat Steps 2, 3 and 4 until AhT = Ah,. This is the operating point of the two pumps in series. 

An alternative to this trial and error procedure for two pumps in series is to calculate AhT from equation 4.33 for various values of the capacity from known values of Ahi and Ah2 at these capacities. The operating point for stable operation is at the intersection of the AhT against Qr curve with the Ahs against Qs curve. 

The injector, columns and valves reside in a low temperature chamber to minimize the loss of deuterium by back exchange (Fig. 12.2). The quenched protein solution is pumped in series through a column containing an immobilized protease and a trap column to capture the peptide fragments. The gradient pump is activated following digestion and the peptides captured on the trap column are eluted and separated over an analytical reverse-phase HPLC column directly into the mass spectrometer. 

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... 

Figure 7.17. Operating points of centrifugal pumps under a variety of conditions, (a) Operating points with a particular pump characteristic and system curves corresponding to various amounts of flow throttling with a control valve, (b) Operating point with two identical pumps in parallel each pump delivers one-half the flow and each has the same head, (c) Operating point with two identical pumps in series each pump delivers one-half the head and each has the same flow.

Multistage several pumps in series in a single casing with the objective of developing high heads. Figure 7.6(c) is of characteristic curves. 

At atmospheric pressure, H2 condenses at -423°F (-253°C). As the pressure rises, the condensation temperature also increases. The liquefaction process utilizes a number of heat pumps in series to reduce the H2 temperature from ambient to the liquefaction temperature. The efficiency of this compression-condensation process ranges from 35 to 60% as a function of size and the refrigerant used in the heat pumps. One of the most efficient refrigerants is a mixture of helium and neon (Quack cycle). The energy consumption of liquefiers theoretically ranges from 5 to 15 kWh/kg... 

It has been found possible to concentrate the heavy isotope in most of the lighter elements by diffusion at low pressures using many mercury diffusion pumps in series.8 Very recently9 the heavy isotope of carbon has been enriched seven fold by circulating twenty-five liters of methane gas for twelve hours at eight millimeters pressure through a battery of thirty-five mercury vapor diffusion pumps, but the yield in the experiment reported was only 1.6 cc. at atmospheric pressure. For tracer experiments in kinetics one needs large quantities with which to work. 

If the energy equation is applied using the source tank at the upper elevation as point 1, the same respective previous equations will also be obtained. In addition, if the energy equation is applied to the system of pumps that are connected in series, the same equations will be produced except that TDH will be the sum of the TDHs of the pumps in series. Also the subscripts denoted by B will be changed to A. See Figure 4.6. 

The vacuum pumping system in a freeze-drying production plant consists of several pumps in series. It has three functions (1) to evacuate chamber and condenser in an acceptable time (10-20 min) to the operation pressure and (2) pump out the gas dissolved in the product at a pressure, which has to be small compared with... 

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