Читать книгу Pump Wisdom - Robert X. Perez - Страница 11

Pumps, of course, are simple machines that lift, transfer, or otherwise move fluid from one place to another. They are usually configured to use the rotational (kinetic) energy from an impeller to impart motion to a fluid. The impeller is located on a shaft; together, shaft and impeller(s) make up the rotor. This rotor is surrounded by a casing; located in this casing (or pump case) are one or more stationary passageways that direct the fluid to a discharge nozzle. Impeller and casing are the main components of the hydraulic assembly; the region or envelope containing bearings and seals is called the mechanical assembly or power end (Figure 1.1).

Many process pumps are designed and constructed to facilitate field repair. On these so‐called “back pull‐out” pumps, shop maintenance can be performed, while the casing and its associated suction and discharge piping (Figure 1.2) are left undisturbed. Although operating in the hydraulic end, the impeller remains with the power end during removal from the field.

The rotating impeller (Figure 1.3) is usually constructed with swept‐back vanes, and the fluid is accelerated from the rotating impeller to the stationary passages into the surrounding casing.

In this manner, kinetic energy is added to the fluid stream (also called pumpage) as it enters the impeller's suction eye (A on Figure 1.3), travels through the impeller, and is then flung outward toward the impeller's periphery. After the fluid exits the impeller, it gradually decelerates to a much lower velocity in the stationary casing, called a volute casing, where the fluid stream's kinetic energy is converted into pressure energy (also called pressure head). The combination of the pump suction (inlet) pressure and the additional pressure head generated by the impeller creates a final pump discharge pressure that is higher than the suction pressure [3].

Figure 1.1 Principal components of an elementary process pump.

Source: SKF USA, Inc. [1].