Centrifugal pumps gears

Positive Pumps. Positive pumps employed by the food industry have a rotating cavity between two lobes, two gears that rotate in opposite directions, or a crescent or stationary cavity and a rotor. Rotary positive pumps operate at relatively low speed. Fluid enters the cavity by gravity flow or from a centrifugal pump. The positive pump also may use a reciprocating cavity, and may be a plunger or piston pump. These pumps are not truly positive with respect to displacement, but are used for metering product flow. 

Example 2 Vibration Consider an electric motor rotating at 1800 rpm driving an 8-vane centrifugal pump rotating at 600 rpm. For this 3 1 speed reduction, assume a gear box having two gears of 100 and 300 tooth. Since 60 Hz is 1 rpm,... 

Previous tests have shown that centrifugal pumps,6 the most reliable and most widely used pumps in the oil industry, are completely unsuitable for pumping oily-witer mixtures. While not entirely satisfactory, positive-displacement pumps, such as screw and gear pumps, cause less droplet breakup than most. 

Passage of emulsion through a centrifugal pump at abnormally low rates and at a high back pressure can shorten the emulsion shear stability. Gear pumps are low-shear devices and do not adversely affect the emulsion. 

Mixed acid and glycerine are stored externally in separate tanks and are transferred by means of centrifugal and gear pumps to small feed tanks. From the feed tanks the reactants are sent to the nitrator by means of two positive displacement pumps driven by the same electric motor. Two speed variators allow change in the total flow rate as well as the ratio between acid and glycerine. The glycerine feed pipe in the nitrator, fitted with a multi-nozzle distributing head is... 

To minimize degradation of impurities, low-speed (1800 rpm) pumps with open impellers should be used. Where solids are large and floc-like, it may be advisable to use a recessed impeller centrifugal pump or a multistage piston pump with suitable aircushioning chambers. Reciprocating pumps should have ball valves. Gear or rotary pumps may be used where solids are not abrasive and filter aid is not present. 

A manufacturer has recently introduced a line of centrifugal pumps which use a gear-speed increaser to drive the impeller at 20,000 rpm with an 1800 rpm motor. One of the pumps delivers a head of 4500 ft. Estimate its impeller diameter. List the most important mechanical design problems for such a pump. 

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