Question

justify the importance of pump, suction head, impelling head and the total head of a pump

Answer 1

What is a Pump?

Introduction to Pumps and its importance.

Moving fluids plays a major role in the process of a plant. Liquid can only move on its own power, and then only from top to bottom or from a high pressure to a lower pressure system. This means that energy to the liquid must be added, to moving the liquid from a low to a higher level.

The important characteristics of a pump are the required inlet pressure, the capacity against a given total head (energy per pound due to pressure, velocity, or elevation), and the percentage efficiency for pumping a particular fluid. Pumping efficiency is much higher for mobile liquids such as water than for viscous fluids such as molasses. Since the viscosity of a liquid normally decreases as the temperature is increased, it is common industrial practice to heat very viscous liquids in order to pump them more efficiently.

Importance of suction head

The Net Positive Suction Head (NPSH) margin is a crucial factor that is commonly overlooked while selecting a pump. It is the difference between the NPSH available (NPSHa) at the pump’s inlet and the NPSH required (NPSHr) by the pump to operate without cavitation. Cavitation is the formation of bubbles at the pump inlet, followed by their sudden collapse, which can cause permanent damage. The NPSH margin value must be positive to avoid cavitation.

Pump designers use NPSH to ensure that pumps will operate without internal damage caused by cavitation under all specified operating conditions.

NPSH can be defined in two parts:

NPSH Available (NPSH_A): The absolute pressure at the suction port of the pump.

NPSH Required (NPSH_R): The minimum pressure required at the suction port of the pump to keep the pump from cavitating.

NPSH or Net Positive Suction Head is a very important part of a pumping system. The systems NPSH_A must be higher than the pump’s NPSH_R in order for proper pump performance and to eliminate the risk of cavitation, which can damage a pump in short order and shut down operations that depend on that pump.

importance of impelling head

In typical pumps used in space rocket engines, an indu-cer is employed upstream of a main centrifugal impellerin order to avoid unacceptable cavitation, improve thesuction performance, and reduce the propellant tankpressure and weight. Inducer design is focused onobtaining sufficient cavitation margin rather than highefficiency. The required net positive suctionhead (NPSH) of a centrifugal pump is reduced byemploying an inducer upstream of a centrifugal impel-ler . Pump efficiency is the ratio of the liquid horsepow-er delivered by the pump and the brake horsepow- er delivered to the pump shaft. When selecting a pump, a key concern is optimizing pumping effi-ciency. It is good practice to examine several perfor-mance charts at different speeds to see if one model satisfies the requirements more efficiently than another. Whenever possible the lowest pump speed should be selected, as this will save wear and tear on the rotating parts. The pump performance curve also gives information on pump efficiency. The efficiency curves intersect with the head-capacity curve and are labeled with percentages. The pump’s efficiency varies through-out its operating range. Each pump will have its own maximum efficiency point. The best efficiency point (BEP) is the point of highest efficiency of the pump. The impeller is subject to axial and radial forces, which get greater the further away the operating point is from the BEP. These forces manifest them-selves as vibration depending on the speed and construction of the pump. The point where the forces and vibration levels are minimal is at the BEP. Pumps should be sized as close as possible to its best efficiency point or flow rate. This not only makes the pump more efficient but also improves

Importance of the total head of a pump

1. Head is the height to which a liquid can be raised by a pump. It is the vertical difference in levels of suction sump to the pump centre + height of the delivery sump from the pump + a quantity to account for the losses in the pipe.
2. Suction height is theoretically limited to 10 m. But in practice it's about 9m. That's the reason why we have to lower the irrigation pump further down once the level goes down in the well.
3. The most important thing is the pump will raise any liquid to the head noted in the name plate whether it's water or brine. The difference in density will show up in the power. Higher the density, higher will be the power consumed.
4. Better the head, you could use it for pumping water to higher heights, for higher head use a reciprocating pump, but discharge will be low for this kind of pumps..!