Pumps impellers

The most important stainless steel [12597-68-1] series are the 200-, 300-, and 400-series. The 300-series, primarily 302, 304, and 316, is used in the dairy industry, whereas the 400-series is used for special appHcations, such as pump impellers, plungers, cutting blades, scrapers, and bearings (Table 11). Surface finishes are specified from No. 1 to No. 8 (highly poHshed) the No. 4 finish is most commonly used. 

T. Dahl and L. Nelik, Computer Aided Design of a Centrifugal Pump Impeller, ASME 85-WA/EE-lO, Washington, D.C., 1985. 

Chemical end uses employ the most exceptional property of PPS, chemical inertness. PPS is almost as chemically resistant as Teflon. It is used in pump impellers and housings and for down-od-weU end uses. New extmsion grades have been developed for potential piping end uses. Coatings of PPS are used extensively. 

The first integral on the right-hand side is the rate of work done on the fluid in the control volume by forces at the boundaiy. It includes both work done by moving solid boundaries and work done at flow entrances and exits. The work done by moving solid boundaries also includes that by such surfaces as pump impellers this work is called shaft work its rate is Ws-... 

Close-Coupled Pumps (Fig. 10-38) Pumps equipped with a built-in electric motor or sometimes steam-turbine-driven (i.e., with pump impeller and driver on the same shaft) are known as close-coupled pumps. Such units are extremely compact and are suitable for a variety of services for which standard iron and bronze materials are satisfactory. They are available in capacities up to about 450 mVh (2000 gal/min) for heads up to about 73 m (240 ft). Two-stage units in the smaller sizes are available for heads to around 150 m (500 ft). 

As the mechanical integrity of the pump system changes, the amplitude of vibration levels change. In some cases, in order to identify the source of vibration, pump speed may have to be varied, as these problems are frequency- or resonance-dependent. Pump impeller imbalance and cavitation are related to this category. Table 10-11 classifies different types of pump-related problems, their possible causes and corrective actions. 

Nucleation The mechanism of crystal nucleation from solution has been studied by many scientists, and recent work suggests that—in commercial crystallization equipment, at least—the nucleation rate is the sum of contributions by (1) homogeneous nucleation and (2) nucleation due to contaci between crystals and a) other crystals, h) the walls of the container, and (c) the pump impeller. If is the net number of new crystals formed in a unit volume of solution per unit of time. 

White cast iron is brittle and difficult to machine. It is made by controlling the composition and rate of solidification of the molten iron so that all the carbon is present in the combined form. Very abrasive- and wear-resistant, white cast iron is used as liners and for grinding balls, dies, and pump impellers. 

An example of a typical turboexpander is shown in Fig. 29-46. Radial-flow turbines are normally single-stage and have combination impulse-reaction blades, and the rotor resembles a centrifugal-pump impeller. The gas is jetted tangentially into the outer periphery of the rotor and flows radially inward to the eye, from which the gas is jetted backward by the angle of the rotor blades so that it leaves the rotor without spin and flows axially away. 

Bronzes Bearings, pump impellers, special-purpose tubing, heat exchanger tubing, screens... 

Damage will be confined to the bubble-collapse region, usually immediately downstream of the low-pressure zone. Components exposed to high velocity or turbulent flow, such as pump impellers and valves, are subject. The suction side of pumps (Case History 12.3) and the discharge side of regulating valves (Fig. 12.6 and Case History 12.4) are frequently affected. Tube ends, tube sheets, and shell outlets in heat exchanger equipment have been affected, as have cylinder liners in diesel engines (Case History 12.1). 

Figure 12.7 Cast iron pump impeller with severe cavitation damage.

Specimen Location Pump impeller and shaft bushing... 

A pump impeller and a shaft bushing from a small cooling water pump assembly were generally corroded. Reddish surface discoloration revealed layer-type dezincification (Figs. 13.14 and 13.15). 

Figure 13.14 A generally dezincified bronze pump impeller. Surfaces are dealloyed to a depth of about 0.020 in. (0.050 cm).

Similarly, graphitically corroded cast iron (see Chap. 17) can assume a potential approximately equivalent to graphite, thus inducing galvanic corrosion of components of steel, uncorroded cast iron, and copper-based alloys. Hence, special precautions must be exercised when dealing with graphitically corroded pump impellers and pump casings (see Cautions in Chap. 17). 

The occurrence of graphitic corrosion is not location specific, other than that it may occur wherever gray or nodular cast iron is exposed to sufficiently aggressive aqueous environments. This includes, and is common to, subterranean cast iron pipe, especially in moist soil (Case History 17.1). Cast iron pump impellers and casings are also frequent targets of graphitic corrosion (Case Histories 17.2 through 17.5). 

Graphitically corroded cast irons may induce galvanic corrosion of metals to which they are coupled due to the nobility of the iron oxide and graphite surface. For example, cast iron or cast steel replacement pump impellers may corrode rapidly due to the galvanic couple established with the graphitically corroded cast iron pump casing. In this or similar situations, the entire affected component should be replaced. If just one part is replaced, it should be with a material that will resist galvanic corrosion, such as austenitic cast iron. 

Sample Specifications 13 in. (33 cm) outside diameter, gray cast iron pump impeller... 

Figure 17.9 Pump impeller that has suffered erosion associated with graphitic corrosion.

The specimen in Fig. 17.15 is part of a cast iron pump impeller. The spongelike surface contours are apparent, as is the black coating that covers surfaces exposed to the cooling water. Microstructural examinations revealed preferential deterioration of the iron matrix surrounding the graphite flakes. 

Figure 17.15 Section of a cast iron pump impeller that has suffered graphitic corrosion followed by cavitation damage.

The pump impeller receives the pumped liquid and imparts velocity to it with help from the electric motor, or driver. The impeller itself looks like a modified boat or airplane propeller. Actually, boat propellers are axial flow impellers. Airplane propellers are axial flow impellers also, except that they are adapted to handle air. 

Pump impellers have some different design eharaeteristics. Among... 

Howe er, most conventional pump impellers receive the fluid into the impeller eye, at the center or inside diameter of the impeller. There are single suction impellers, and dual or double suction impellers with two eyes, one on each side. Dual suction impellers are mostly specified for low NPSH applications because the eye area is doubled (it ean reeeive twice as much fluid at a lower velocity head). Dual suction impellers arc mostly found on split case pumps where the shaft passes completely through the impeller. But they can afso be found mounted onto the end of the shaft in some special pump designs. 

There is more information on this in Chapter 9. Dual volute casings tend to equalize the radial hydraulic forces around the pump impeller, thus expanding the operating window of the pump. The Ns is a guide in selecting the adequate volute design. 

By dynamically balancing most parts, seal life and bearing life is greatly improved, even on smaller equipment. Dynamic balancing is needed on pump impellers, as the practice of static balance is woefully inadequate. Vertical pumps must be dynamically balanced the long, slender shafts are highly susceptible to any unbalanced-induced vibration. 

This corrosion is most pronounced in locations of high velocity, turbulence, and impingement, such as at elbows, weld reinforcements, pump impellers, steam injection nozzles, and locations where freshly condensed fractions drip upon or run down metal surfaces. 

Amongst the many other applications for acetal resins should be mentioned links in conveyor belts, moulded sprockets and chains, blower wheels, cams, fan blades, check valves, pump impellers, carburettor bodies, blow-moulded aerosol containers and plumbing components such as valve stems and shower heads. 

F-G F Thermoforming, injection, blow, rotational and extrusion molds Business machine and camera housings, blowers, bearings, gears, pump impellers... 

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