Understanding the Characteristics & Construction of Centrifugal Pumps

1. Understanding the Characteristics & Construction of Centrifugal Pumps

2. A centrifugal pump turns the energy of the prime mover into kinetic energy, which is then transferred into the pressure energy of the fluid being pumped. It has a central eye on the impeller through which the fluid enters the pump. The fluid is accelerated radially outward from the pump casing by the high-speed impeller. This raises the fluid pressure, causing it to be pushed out of the way. Let’s understand a little more about centrifugal pumps

3. Characteristics of a Centrifugal Pump Capacity The rate of liquid flow through the impeller, expressed in gallons per minute (gpm) or cubic meters per hour (m3/h), is the capacity of a pump. Efficiency The ratio of the output power to the input power multiplied by 100 is the efficiency in percent with which the pump operates. Efficiency rises and falls with capacity, reaching a peak at one capacity where the sum of all losses is the smallest.  At high flow rates and moderate heads, centrifugal pumps are more efficient than at low flow rates and high heads.

4. Total head The energy per unit weight of a fluid due to its Elevation head  It is generally expressed in feet (or meters) as the height of a water column required to create a given pressure. The discharge head minus the suction head equals the total head created by a pump. On the discharge side of the pump, the discharge head is the energy per unit weight of fluid. On the suction side of the pump, the suction head is the energy per unit weight. The static head is the static elevation in feet (meters) measured at the same location as the pressure. If a pressure gauge is employed, the measuring point for the static head is the middle of the gauge. For such measurements, the centre line of the pump impeller is commonly employed as a reference point. In this section, the symbols and units are the same as those used by the Hydraulic Institute.

5. Net Positive Suction Head The entire suction head in feet (metres) of liquid in absolute pressure terms measured at the pump impeller, minus the vapor pressure of the liquid in feet, is known as net positive suction head (NPSH) (meters). The pump's net positive suction head required (NPSHR) is established by testing and is the NPSH value at which the total head of the pump has lowered by 3% due to the pump's low suction head and the ensuing cavitation the 3 percent head decrease in multistage pumps pertains to the first stage head, while the NPSHR rises with capacity. Speed A centrifugal pump is usually operated by an electric motor with a constant speed. A variable-speed drive, on the other hand, is more efficient at controlling a pump. The additional expense of variable-speed drives can be justified by the energy savings that occur.

6. System Head Curve The pump must provide a total head equal to or greater than the total head required by the system in order to transfer liquid through any system of pipes. The system head curve is displayed against capacity and shows how the system head increases with flow rate. The curvature of the system head curve is a key factor to consider when choosing a pump for building services. The combination of the static head plus the head due to friction loss in the system is the total head required to pump liquid through a system.

7. Pumping water to the top of a 50-foot (15-meter) building, for example, requires a total head of 50 feet (15 metres) plus some friction loss. The total head required is 60 feet (3 m) if the friction loss at the required flow is comparable to a head of 10 ft. (3 m) (18 m). Because there is no friction loss when the flow is zero, the total head required is only 50 feet (15 m). The pump will turn on when the pump curve crosses the system head curve; at this moment, the pump will pump the entire needed flow. The pump is subject to wear because the total head output is reduced. As a result, the flow has decreased. However, when there is a high static head, the reduction is larger than when the head is due solely to friction losses. As a result, it's critical to examine the system head curve and pump characteristic curve when choosing a pump to ensure that a 10% drop in pump output due to wear doesn't result in a considerable loss in flow rate.

8. Construction of Centrifugal Pump Material: Cast-iron casings, bronze impellers, and bronze minor parts are employed in centrifugal pumps used in most building functions. Impellers and tiny pieces made of stainless steel are also common. Although cast-iron impellers can be employed, their lifespan is shorter than that of bronze or stainless-steel impellers Shafts, Seals and Bearings The shaft that drives the pump's impeller enters the casing through a hole that must be sealed to keep the shaft from leaking (i.e., the seal must prevent liquid from leaving and air from entering). Soft fiber packing and mechanical face seals are the two types of seals used. The shaft enters the hole through a stuffing box when packing is utilized Without removing the pump, the packing material, which is quite affordable, may generally be replaced. However, the packing will leak roughly 60 drips per minute and will need to be adjusted on a regular basis. Mechanical seals are frequently used instead of packing because they are dependable, have a long life expectancy, are almost leak-free, and do not need to be adjusted on a regular basis.

9. How to choose a good pump? When selecting a pump, you should first evaluate the application's volume and pressure requirements, as well as the material to be pumped. Oil, fertilizer, and other chemicals, in addition to pure water, may be pumped. You should also look into horsepower needs, particularly in terms of discharge pressure and volume.

10. Centrifugal pumps are well-known for their ability to tolerate suspension.  Price Pumps provide the best seal less, horizontal and vertical centrifugal pumps. For details, visit https://www.pricepump.com/ Source: https://www.knowpia.com/s/blog_151013c4c1caad9e