Design considerations Pumping systems

This is an important part of the pump system and should be thought of as a very speeialized piping design. Considerable attention must be direeted to the pump suetion piping to ensure satisfactory pump operation. 

Typical design considerations include feed water flow rates, water and air temperatures, tower feed and discharge systems (gravity feed or type and location of pumps), and influent contaminant concentrations. In addition, requirements for effluent water contaminant concentrations and restrictions on air emission should be considered according to the various federal and state regulations. 

A useful feature of the PD pump is that for a given power input Eqs. (159)—(161) allow the designer considerable flexibility in adjusting discharge pressure, cylinder capacity, and overall capacity. Positive displacement pumps are favorites on large-scale, high-pressure systems. Details of each of the various types of PD pump are best obtained from individual vendors. 

Significant amounts of condensables as load to the vacuum system can be an important consideration in the design and selection of the vacuum pump. Vacuum system suppliers must be provided condensable data in order to properly design the vacuum system. Information required include molecular weight, vapor pressure, specific heat, latent heat, transport properties, and solubility in water. 

In addition, other laws, including the Fire Act, stipulate what should be taken into consideration in designing as to the performance of fire detectors and the water sources of fire fighting water supply systems. Redundancy and diversity of the fire fighting pump system and compliance to the law on the location and numbers are confirmed in the course of PSR, as well. 

For pumped systems rapidly increasing energy costs have aroused considerable interest in designing for very low valve-pressure drops. This pushes us toward line-sized valves. If piping and equipment pressure drops are large in comparison with valve-pressure drops, valve turndown sui rs (becomes smaller). The installed flow characteristic also becomes very different ftom the inherent flow characteristic. A linear valve tends toward an installed square-root flow characteristic, while an equal-perccntJ e valve tends toward an installed linear characteristic. At the hi -flow, high-lift end of the plot, however, all curves, r ardless of y alve inherent characteristic, level off at a maximum flow. This is so because the valve has run out of pressure drop. 

Until very recently liquid hydrogen has been in limited supply and its use has been restricted to small quantities at any one time. The transfer of small quantities of liquid from storage dewars to the use points has been effected by pressurization of the dewar with hydrogen or helium gas or by the use of specially designed centrifugal pumps. As the use of liquid hydrogen for missiles and for other activities increases, the quantity of gas required to pressurize and transfer the liquid from a dewar becomes large audits cost and that of the pressure vessel required become important considerations in the selection of the type of transfer system to be used. 

In terms of purely hydraulic considerations, pump performance can be achieved with many pumping systems. The control of different rotary pump devices maybe more difficult. Designs that include implanted sensors such as pressure or flow sensors must deal with drift of these signals. Signal-to-noise ratios are often poor in devices that must operate continuously for several years in a noisy environment. Designs that employ few or no sensors are preferable but must rely on a model of the system, and the system can change unpredictably over time. 

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