Types Of Chemical Pumps

The second step in selecting a chemical pump is to determine which type of pump is required, based on the characteristics of the liquid and on the desired head and flow rate.

FIGURE 1 Cutaway of a typical centrifugal chemical pump (Flowserve Corporation)

It should also be noted that not all types are available in every material of construction, and the final selection of pump type may depend on the availability of designs in the proper material.

Centrifugal Pumps Centrifugal pumps (Figure 1) are used extensively in the chemical industry because of their suitability in practically any service. They are available in an almost unending array of corrosion-resistant materials. Although not built in extremely large sizes, pumps with capacity ranges of 5000 to 6000 gpm (1100 to 1400 m3/h) are commonplace. Heads range as high as 500 to 600 ft (150 to 180 m) at standard electric motor speeds. Centrifugal pumps are normally mounted in the horizontal position, but they may also be installed vertically, suspended in a tank, or hung in a pipeline similar to a valve. They are simple, economical, dependable, and efficient. Disadvantages include reduced performance when handling liquids of more than 500 SSU (108 cSt) viscosity and the tendency to lose prime when comparatively small amounts of air or vapor (3 to 5 percent) are present in the liquid.

Rotary Pumps The gear, screw, deforming-vane, sliding-vane, axial-piston, and cam types are used for high-pressure service. They are particularly adept at pumping liquids of high viscosity or low vapor pressure. Their constant displacement at a set speed makes them ideal for use in metering small quantities of liquid. Because they operate on the positive displacement principle, they are inherently self-priming. When built of materials that tend to gall or seize on rubbing contact, the clearances between mating parts must be increased, with the result of decreased efficiency. The gear, sliding-vane, and cam units are generally limited to use on clear, nonabrasive liquids.

Diaphragm Pumps These units are also classed as positive displacement sealless pumps because the diaphragm acts as a limited displacement piston. Pumping action is obtained when the diaphragm is forced into reciprocating motion by mechanical linkage, compressed air, or oil from a pulsating external source. This type of construction eliminates any connection between the liquid being pumped and the source of energy and thereby eliminates the possibility of leakage. This characteristic is of great importance when toxic or very expensive liquids are being handled. Disadvantages include a limited selection of corrosion-resistant materials, limited head and capacity range, and the necessity of using check valves in the suction and discharge nozzles. Although air-operated diaphragm pumps are displacement pumps, they are not positive displacement pumps. The maximum pumping pressure cannot exceed the pressure of the compressed air powering the pump. Refer to Section 3.6 for more details on diaphragm pumps.

Regenerative Turbine Pumps Flow rates up to 100 gpm (23 m3/h) and heads up to 700 ft (210 m) are easily handled with this type of pump. When it is used for chemical service, the internal clearances must be increased to prevent rubbing contact, which results in decreased efficiency. These pumps are generally unsuitable for solid-liquid mixtures of any concentration.

Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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