Fluid-moving Machinery

Fluids are moved through pipe, equipment, or the ambient atmosphere by pumps, fans, blowers, and compressors. Such devices increase the mechanical energy of the fluid. The energy increase may be used to increase the velocity, the pressure, or the elevation of the fluid. In the special case of liquid metals energy may be 

From the standpoint of fluid mechanics the phenomena occurring in these devices can be classified under the usual headings of incompressible and compressible flow. In pumps and fans the density of the fluid does not change appreciably, and in discussing them, incompressible-flow theory is adequate. In blowers and compressors the density increase is too great to justify the simplifying assumption of constant density, and compressible-flow theory is required. 

In all units certain performance requirements and operating characteristics are important. Flow capacity—measured usually in volumetric flow per unit time at a specified density—power requirements, and mechanical efficiency are obviously important. Reliability and ease of maintenance are also desirable. In small units, simplicity and trouble-free operation are more important than high mechanical efficiency with its savings of a few kilowatts of power. 

In pumps, the density of the fluid is both constant and large. Pressure differences are usually considerable, and heavy construction is needed. 

DEVELOPED HEAD. A typical pump application is shown diagrammatically in Fig. 8.5. The pump is installed in a pipeline to provide the energy needed to draw liquid from a reservoir and discharge a constant volumetric flow rate at the exit of the pipeline, Zj, feet above the level of the liquid. At the pump itself, the liquid enters the suction connection at station a and leaves the discharge connection at station b. A Bernoulli equation can be written between stations a and b. Equation 

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The main function of most lubricants is to reduce friction and wear between moving surfaces and to abstract heat. They also have to remove debris from the contact area, e.g. combustion products in an engine cylinder, swarf in metal-cutting operations. Sometimes they have to protect the lubricated or adjacent parts against corrosion, but this is not a prime function of most lubricants. On the other hand, many lubricants do contain corrosion inhibitors and some lubricating oils, greases, mineral fluids and compounds are specially formulated to prevent the corrosion of machinery or machine parts, particularly when these components are in storage or transit. These temporary protectives are described in Section 17.3. 

Hydraulic power transmission is used for slow-moving, powerful machinery requiring accurate control, or where load factors are very low. Efficiencies of hydraulic operation range up to 0.85, the chief loss being that due to the friction at cup leathers used for plunger packings. For direct steam pumps having the same number of fluid cylinders as steam cylinders, the ratio of areas of steam... 

Contact with or caught in or between moving parts of machinery Release of pressurised gas or fluid Contact with sharp object... 

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