Centrifugal pumps sump pumps

Sump pumps can draw water up from levels as much as 30 ft below the pump s suction. But do such pumps require NPSH Absolutely All centrifugal pumps have some NPSH requirements. What, then, is the available NPSH to the sump pump shown in Fig. 25.8 ... 

The only real difference between a sump pump and an ordinary centrifugal pump is that the sump pump is more difficult to prime than the ordinary pump. 

Turbine pumps mix features of a simple propeller (axial flow) pump with a centrifugal pump and are often referred to as units with mixed flow. A simple turbine pump carries curved vanes on a central rotating spindle. Such pumps are often immersed in the liquid and find use in closed-loop circulation systems, in condenser circulating water, and in sumps and wells. Turbine pumps have noteworthy pumping capacity, and like positive displacements pumps are often used for heads up to about 100 ft/stage with capacities of up to several hundred gallons/minute. 

Many centrifugal pumps are built for specific service and are classified by their intended service, such as general-purpose pump, boiler-feed water pump, sluny pump, sump pump, hot oil pump, etc. 

From the degassing area discharge, each fuel stream flows to the suction of a variable speed centrifugal sump type pump. Each pump is designed to deliver about 9000 gpm at 20-ft head of pumped fluid. To obtain a reasonable pump speed, the net positive suction head requirement is 11.5 ft. A gas pressure (helium) is maintained o er the pump sump to prevent flooding of upper parts (motor windings, cooling system, etc.) of the pump. 

Suppose that, instead of using a PD pump, in Example 9.2 we used a centrifugal pump, which for 200gal/min had a reported NPSH requirement of 10 ft. What would be the maximum elevation above the sump at which we could place the pump ... 

A self-flushed pump with a single set of mechanical seal faces can leak the process fluid into the environment. If the process fluid is hydrocarbons, this sort of leakage is no longer permitted by the EPA. The sketch I have shown in Fig. 37.1 does not represent the actual configuration of a double mechanical seal component, but does explain the function of the individual pump internal components (see reference 2 for an excellent description of the actual arrangements of the internals for an overhimg, wet sump, centrifugal pump). 

Recycle is from the bottom of the sump. A bleed stream from the lower portion of the crystallization zone goes to byproduct recovery, consisting of hydrocyclones, and a filter or centrifuge. The gypsum byproduct contains 5-10% moisture depending on requirements. Recirculation pumps convey the limestone slurry from the conical bottom sump to the various spray levels. 

The forepump is of the centrifugal type and has very low NPSH requirements. The pump is driven by a canned motor, which, as the sketch indicates, is directly immersed in the suction liquid. The pump discharges into the sump, which acts as surge chamber during the compression stroke, during which no liquid enters the high-pressure pump. 

Fig. 15-2. Sump-type centrifugal pump developed for the Aircraft Reactor Experiment.

Pumps for both the sodium and the molten-fluoride mixture consisted of sump-type centrifugal pumps with overhanging shafts. The pumps were mounted vertically, and a gas space was provided between the liquid level and the upper bearings of the pump. The pumps were located so that the free-liquid surface in the sump tank was the high point in both the fuel and the sodium circuits. The sump tank of the pump also served as an expansion tank for the liquid. The isometric drawing of the fuel system presented in Fig. 16-5 indicates the relative levels of the components. 

In another experiment [27] NF.PA circulated bismuth with a 50-gpm centrifugal pump for 100 hr at a mean temperature of 1500°F with a temperature differential of 500°F. An accumulation in the sump of a residue high in oxide content and dissolved elements reduced the flow and forced suspension of operation. This residue probably resulted from an impure inert atmosphere above the liquid metal. The container material selected was AISI type-347 stainless steel which had shown some promi.se in bismuth solubility tests at temperatures up to 1800°F. 

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