Centrifugal Pump Also Submersible and Turbine

There are several types of centrifugal pumps; the distinction lies in the design of the impeller. They include radial, mixed, and axial flow, turbine, close-coupled, submersible, and adjustable blade impeller pumps. Water is admitted into the suction pipe or pump casing and is rotated in the pump by an impeller inside the pump casing. The energy is converted from velocity head primarily into pressure head. In the submerged multistage, turbine-type pump used to pump water out of a well, the centrifugal pump is in the well casing below the drawdown water level in the well; the motor is above ground. In the submersible pump, the pump and electric motor are suspended in the well attached to the discharge pipe, requiring a minimum 3-inch- (preferably 4-inch-) diameter casing. It is a multistage, centrifugal pump unit.

If the head against which a centrifugal pump operates is increased beyond that for which it is designed and the speed remains the same, then the quantity of water delivered will decrease. By contrast, if the head against which a centrifugal pump operates is less than that for which it is designed, then the quantity of water delivered will be increased. This may cause the load on the motor to be increased, and hence overloading of the electric or other motor, unless the motor selected is large enough to compensate for this contingency.

Sometimes two centrifugal pumps are connected in series so that the discharge of the first pump is the suction for the second. Under such an arrangement, the capacity of the two pumps together is only equal to the capacity of the first pump, but the head will be the sum of the discharge heads of both pumps. At other times, two pumps may be arranged in parallel so that the suction of each is connected to the same pipe and the discharge of each pump is connected to the same discharge line. In this case, the static head will be the same as that of the individual pumps, but the dynamic head, when the two pumps are in operation, will increase because of the greater friction and may exceed the head for which the pumps are designed. It may be possible to force only slightly more water through the same line when using two pumps as when using one pump, depending on the pipe size. Doubling the speed of a centrifugal pump impeller doubles the quantity of water pumped, produces a head four times as great, and requires eight times as much power to drive the pump. In other words, the quantity of water pumped varies directly with the speed, the head varies as the square of the speed, and the horsepower varies as the cube of the speed. It is usual practice to plot the pump curves for the conditions studied on a graph to anticipate operating results.

The centrifugal pump has no valves or pistons; there is no internal lubrication; and it takes up less room and is relatively quiet. A single-stage centrifugal pump is generally used where the suction lift is less than 15 feet and the total head not over 125 to 200 feet. A single-stage centrifugal pump may be used for higher heads, but where this occurs, a pump having two or more stages, that is, two or more impellers or pumps in series, should be used. The efficiency of centrifugal pumps varies from about 20 to 85 percent; the higher efficiency can be realized in the pumps with a capacity of 500 gpm or more. The peculiarities of the water system and effect they might produce on pumping cost should be studied from the pump curve characteristics. A typical curve is shown in Figure 2.18. All head and friction losses must be accurately determined in arriving at the total pumping head.

Centrifugal pumps that are above the pumping water level should have a foot valve on the pump suction line to retain the pump prime. However, foot valves sometimes leak, thereby requiring a water connection or other priming

. _ 22 brake horsepower

14U Shut-off head = 260'

. _ 22 brake horsepower

14U Shut-off head = 260'

220 — centrifugal pump, known rpm

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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