NPSH means minimum head is required to pump the liquid through impeller eye.

You have to fill the centrifugal pump with fluid before it starts to move fluid. It means filling the pump with liquid to get it to pump because the pump will not fill itself with liquid from being dry. These pumps cannot suck fluid in by creating a vacuum in the pump chamber like other types of pumps.

A centrifugal pump takes up little space as compared to a plunger pump and weighs little. So, minimal structural reinforcement is required for the load bearing floor space. It has a low initial cost as well as low maintenance cost since all motion is rotary and there are no sensitive parts such as the valves in a plunger pump. Also, this pump needs no air vessels or alleviators. This pump can be keyed directly to a power source as it generally has high working speeds and needs no stepping. A centrifugal pump can handle muddy, dirty and corrosive liquids it can pump water at temperatures of up to 400 º and circulate oil at high temperatures providing it reaches the pump at high pressure i.e. a full pressure system. The discharge of liquid is continuous and without shock, the flow can be controlled from full flow to no flow without shutting the pump down or damaging the pump or pipes thereby providing suitable switching gear has been installed.

Centrifugal pumps are used for all straight pumping applications of low viscosity fluids like water without complications, such as liquids containing hard solids. These pumps can be single stage, or they can be stages stacked in a series-flow arrangement to deliver high output pressures. Centrifugal pumps are simple in concept and construction and deliver the highest flow performance at moderate pressures. Centrifugal pumps are available in materials which include all metals, plastics, and ceramics.

Centrifugal pump is used in plumbing in order to propel liquids in the pipes. The pump uses a spinning bit that raises the pipe pressure in order to move the liquid. Such pumps can be used in homes and buildings to increase the plumbing system’s efficiency. It can also be used in outdoor pools, ponds and other decorative water features.

A centrifugal pump is simple and easy to be handled. It comes with a rotating impeller in a chamber and a motor that is used to turn the impeller. Centrifugal pumps consist of two forms: horizontal pumps that come with horizontal impeller shafts and vertical impellers that come with vertical pumps. The vertical impeller work like a sump pump, in an opposite orientation. The most common problems with a centrifugal pump are the sound that it makes or a change in the pump’s suction rate. There are five problems that are directly found when the pump is in operation and the three problems that can be ascertained from the pump’s maintenance files.

Centrifugal pumps spin water using the propellers that are located inside housing or a casing. As the propellers spin the pressure builds outwards and the water is pushed through the path. These pumps work by converting the rotational kinetic energy from an electric motor or turbine to an increased static fluid pressure.

You can also refer it as a “close-coupled pump” in which the pump is mounted directly on the same shaft as the driving motor. There is no base plate or coupling to join the two shafts, drive and driven, and the pump hangs off the motor frame. A centrifugal pump is a type of pump where the liquid is forced to travel by an impeller which is inside a close-fitting chamber or “volute” – it is probably the most common industrial and domestic pump type.

A centrifugal pump cannot pump air, therefore cannot self prime, like a positive displacement pump.

Generally, centrifugal pumps are high discharge, low pressure generating pumps. In order to increase the pressure thus generated, it is setup in stages wherein pressure increases from one stage to another. We often see this in daily life applications such as pumps for water tankers. Even emergency fire fighter vehicles use this type of pumps. These are called dynamic or non-positive displacement pumps.

Recognizing erosion and corrosion in a centrifugal pump can be done by one of three mediums depending upon the area affected. It can be done visually or by microscopic examination or with the use of inspection tools such as dyes and magnetic particles. Some of the most apparent signs of a problem include loss of pressure and efficiency, low fluid flow rate and an increase in operational costs. Any of these indicators warrant further investigation.

Centrifugal pump uses centrifugal force to move the water through plumbing systems and hoses. The centrifugal pump spins a shaft at high speed which in turn rotates an impeller to create a vacuum through centrifugal force that pulls the water. A mechanical seal is positioned just behind the spinning impeller on the motor shaft which prevents water from entering the delicate electrical motor of the pump. Replacing these mechanical seals will mean opening the pump system, removing the impeller from the pump’s shaft and sliding the old seal off the shaft.

The impeller pump increases the pressure. The flow has velocity energy via impeller and the energy change to pressure energy in diffuser.

It depends on the specific pump. Most of the pumps come with the impeller, the wear ring and mechanical seal. However, a pump with a packed stuffing box comes with the packing and some pumps consist of the shaft coupling.

Cavitations is caused when vapor pressure in the fluid in higher when compared to the surrounding pressure. In centrifugal pump, when the hydraulic pressure (due to height) in the fluid falls below the vapor pressure of the fluid itself, cavitations will occur.

To determine the critical speed, it is important to note that any object made from an elastic material and metal has a natural period of vibration. This happens because the pump rotating assembly is not uniform around the center line of the shaft. So it is common that getting variations in the density of the materials as well as manufacturing tolerances and casting irregularities contributing to the problem. This eccentricity produces deflection when the rotating assembly rotates at the speed the centrifugal force exceeds the elastic restoring forces. At this speed the assembly will vibrate as if it were unbalanced, and can fail the seal, bearings or fatigue the shaft itself. The lowest speed at which this happens is called the first critical speed.

If you are pumping from a tank you have to lower the pump in relation to the height of the water in the tank. The more feet of water above the center of the pump, the greater your net positive suction head. If that is not possible you have to have a pump to increase the pressure of the water coming into the eye of the pump impeller.

The balancing disc has a wear ring bolted to its face. The balancing disc is removable and provides an easy way to replace the wear ring without removing the pump or dismantling the entire pump. The wear ring thrusts against another wear ring bolted to the counter disc. This mechanism prevents the rotating element from exceeding its travel which would result in loss of efficiency and later damage the impellers. The two wear rings in a pump are made of brass and the other of steel respectively.

We know that the ship’s engine room contains different types of pumps including centrifugal pumps. We have also seen that how a planned maintenance schedule is carried out on board ships for maintaining the equipments. The following steps describe the entire process to disassemble, inspect and reassemble a centrifugal pump in a chronological order:

• Switch off supply from the control room and isolate breaker with masking tape and place a safety board (Men at work).
• Switch off supply from local panel and isolate by masking tape, place a safety board on the panel (Men at work).
• Close suction and discharge valves and lash them with rope.
• Drain the suction pipe and ensure water is not coming, and then loosen or crack open the joints and ensure that pump is safe for opening.
• Fix chain block and ensure its cable length and strength is satisfactory.
• Mark on coupling and casings and then remove the coupling bolts.

It will over heat and resize. The liquids that a centrifugal pump moves also act as the lubricant and cooling system for the pump.