Positive displacement pumps selection

Selection of pump for a given appHcation is not a trivial task. Often more than one pump type can accomplish the required job. Thus a final choice on a pump type is often a result of personal experience and usage history. As a rule of thumb, the choice of a kinetic, such as centrifugal, or a positive displacement pump is made on the basis of the specific speed. Whereas specific speed is appHcable primarily for centrifugal but not positive displacement pumps, the US value can be used as a guide. Generally, for calculated values of specific speed, eg, nS > 10 [NS > 500), kinetic-type pumps are usually selected. For nS < 10 [NS < 500), positive displacement pumps are typically appHed. 

There are several important calculations that are needed to properly evaluate and select the appropriate positive displacement pump [17,18,19,20,21]. 

If a centrifugal is not suitable, select a rotary positive displacement pump. The design usually selects itself. 

Figure 10.63. Selection of positive displacement pumps (adapted from Marshall (1985)). Descriptions of the types mentioned are given in Volume 1, Chapter 8...

Select a 10-gpm positive displacement pump, carbon steel construction. A summary of the equipment needs for the alkylation unit in this preliminary process design is presented in Table 1. The preparation of similar equipment lists for the other process units completes the equipment selection and design phase of the preliminary design. Figure 2-5 shows a simplified equipment diagram for the proposed process and includes the specified size or capacity of each piece of process equipment. 

The most commonly used vacuum pumps are steam-jet ejectors and several positive-displacement pumps, which are shown in Figures 5.1 and 5.2. Some of the characteristics of vacuum pumps are given in Table 5.1. A prime consideration when selecting a vacuum pump is the compatihility of a gas with a seal fluid. To avoid these problems, there is a trend toward using dry pumps where a seal fluid or lubricant is not used [60]. 

Figure 10.62. Selection of positive displacement pumps [adapted from Marshall (1985)].

The selection of a suitable rotary positive-displacement pump for a viscoplastic material has been discussed by Steffe and Morgan [1986]. 

Power consmnption the operating point of centrifugal pump should be chosen at the highest efficiency possible. Generally, the vendors/manufacturers offer a range of models, which cover the requirements of capacity, head, etc. However, the final selection should be done while keeping in mind the most likely (normal) condition in which the pump will be ran. In case of positive displacement pumps the performance curves should be studied to select proper speed for the capacity and required head... 

Positive displacement pumps like for example mono-type pumps are recommended for all ether sulphate paste duties. Pipe diameter selection has been discussed in section 5.6.1., chemical engineering aspects related to neutralisation reactor systems. Paste velocities of approximately 0.5 m/s should be the basis for pipe diameter calculations. 

Several types of pumps are useful for handling slurries. The selection of a pump for a specific slurry transport line is based on the discharge pressure requirement and the particle characteristics (particle size and abrasivity). The pumps that are used are either positive displacement pumps or centrifugal (rotodynamic) pumps. 

Later in this chapter, we formally set out the tools used for sizing head losses. The elements used for selecting pumps are introduced in Chapter 5. Different types of pumps are presented (centrifugal pumps, axial pumps, positive displacement pumps), and the reasoning that guides the choice of a pump, based on the levels of flow rate and head to be delivered, is discussed. 

A variety of positive and nonpositive displacement pumps are available for use in fuel and fuel additive systems. Selection is based on application, required flow and cost. The primary differences in positive displacement and nonpositive displacement pumps are described in TABLE 9-9. 

A wide variety and numerous suppliers of automated dispensing equipment are available as listed in Table 4.22. An important consideration in selecting an automated, contact-type dispensing system is the pump used in the system, of which there are three types time-pressure, auger, and linear piston or positive displacement. " ... 

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