Practice Questions

Multistage centrifugal pumps are used to produce high heads by connecting multiple liquid chambers (or stages) in series. The more stages the pump has, the higher the final discharge pressure, but the flow range always remains constant for a given rpm.

A centrifugal pump should be started with its delivery valve closed to prevent backflow from the reservoir. The delivery valve connects the pump outlet and delivery pipe and is opened once the pump builds up its pressure to control or vary the discharge.

Priming is the process of filling the suction pipe, casing, and delivery pipe of a centrifugal pump with fluid before starting it, to drive out air voids

The efficiency of a centrifugal pump is highest when its blades are bent backward. Backward-curved vanes are commonly used as they operate at higher efficiency than forward-curved vanes.

For a centrifugal pump, the ratio of power actually gained by the fluid to the shaft power supplied is known as overall efficiency.

A fundamental characteristic of a centrifugal pump is that when the fluid enters the impeller (the rotating component), it is typically flowing purely radially, which means it has no tangential or whirl component of velocity

Slip will decrease with the increase in flow rate

Fluid is considered to have friction while flowing inside the pump

There will be no whirl component of velocity at the entry to impeller

The specific speed (NS) of a centrifugal pump is given by $\frac{N\sqrt{Q}}{H^{\frac34}}$

Cavitation in a centrifugal pump can be reduced by decreasing the suction head. This is because cavitation occurs when the pressure at the suction side of the pump drops below the vapor pressure of the liquid.

A cetrifugal pump converts kinetic energy into pressure energy. The pressure rise in the impeller should be equal to the manometric head, which is the difference in pressure between the pump's inlet and outlet points.

The double feed pump a type of reciprocating pump where water is discharged in each stroke of the piston as water is displaced by both sides of the piston. It is commonly employed for medium size boilers.

The centrifugal pump works on the principle of forced vortex flow, with the flow in a radial outward direction. It acts as a reverse of an inward radial flow reaction turbine.

Forward curved blades has higher efficiency.

Backward curved bladed produces higher pressure ratio.

Backward curved blades has poor efficiency.

Forward curved blades produces higher pressure ratio.

A centrifugal pump works on the principle of force vortex. The impeller generates velocity through rotation and the casing converts it into pressure. Inside the impeller, the flow is forced vortex, while outside the casing it is free vortex due to the absence of external torque.

The flow in a centrifugal pump casing is in the radial outward direction, acting as a reverse of an inward radial flow reaction turbine.

pump increases fluid pressure by imparting energy from an external prime mover to the impeller. The fluid gains kinetic energy and leaves the impeller radially, resulting in a flow that is radially outwards.

works on the same principle as that of a Francis turbine

A centrifugal pump used for pumping liquids containing suspended solids has an open impeller. This type of impeller is suited for handling slurries and liquids with high amounts of suspended bodies, such as sewage.

An air vessel is a chamber that is used in reciprocating pumps to smooth out the flow of fluid and reduce pulsations. It is typically fitted in the delivery line of the pump, between the pump and the customer's system.

Reciprocating pumps use pressure to discharge a certain volume of liquid. The slip of a pump is the difference between theoretical and actual discharge due to leakage. Negative slip occurs when actual discharge is greater than theoretical discharge. Mathematically, negative slip equals Qact - Qth

Theoretical discharge is more than actual discharge

Actual discharge is more than theoretical discharge

Theoretical discharge is equal to actual discharge

Centrifugal pumps have a simple and versatile design, with the liquid entering at the center of the impeller.

Reciprocating pumps displace liquid with a piston or plunger. They are best suited for small capacities and high heads. Air vessels can be used to even out flow and save power, especially in single-acting pumps. The percentage of work saved in pipe friction by fitting air vessels in a single- acting pump is approximately 84.8% and in a double-acting pump, it is approximately 39.2%.

The flow from a reciprocating pump may be evened out by employing properly phased out multicylinder units or by fitting air vessels close to the cylinder

Percentage of power saved by fitting air vessel is more in a double acting pump than in a single acting pump

The reciprocating pump is essentially a low speed machine and that speed is limited due to considerations of flow separation

The reciprocating pumps can handle only low viscosity liquids free from impurities

Slip in a pump reduces the liquid transfer, as it causes the tangential component of the liquid to decreases

Centrifugal pumps dealing with muds require an open impeller as it is designed to handle abrasive liquids such as water, sand, pebbles, muds, and clay with solid contents up to 25%. Closed impellers are meant for clear water, hot water, and acids only, while semi-open impellers are used for industrial pump problems that require a rugged pump to handle liquids containing fibrous material.

Product of manometric and mechanical efficiencies

Ratio of manometric efficient to mechanical efficiency

Product of manometric and hydraulic efficiencies

Ratio of mechanical efficiency to manometric efficiency

The flow in the volute casing outside the rotating impeller of a centrifugal pump is a free vortex flow. This is because the external torque is absent outside the casing, causing the fluid to have a vortex motion due to the inertia of the fluid.

A centrifugal pump acts as a reverse of an inward radial flow reaction turbine, which means that the flow in centrifugal pumps is in the radial outward direction

Inversely proportional to the square of speed of its impeller

Directly proportional to the speed of its impeller

Inversely proportional to the speed of its impeller

Directly proportional to the square of speed of its impeller

The specific speed of a centrifugal pump is the speed of a similar pump that would deliver one cubic meter of liquid per second against a head of one meter.
the specific speed is the speed of a similar pump that would deliver unit discharge at unit head

Hydraulic ram develops maximum impulse when valve closes suddenly. This is due to the small water hammer effect closes supply pipeline.

A hydraulic intensifier typically consists of a fixed ram, a hollow inverted sliding cylinder, and a fixed inverted cylinder. It is used to increase pressure of hydraulic fluid or water using hydraulic energy from a large quantity of fluid at low pressure. Option 3 is the correct answer.

Two cylinders, two rams and a storage device

A cylinder, a piston, storage tank and control valve

Oil spreads on the surface of water due to the surface tension effect. The greater surface tension of water pulls oil in all directions, causing it to spread on the water.

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