Reciprocating Pump MCQ Quiz in मराठी - Objective Question with Answer for Reciprocating Pump - मोफत PDF डाउनलोड करा

Explanation:

Pumps

• The hydraulic machines which convert the mechanical energy into hydraulic energy are called pumps.

Reciprocating pump:

Reciprocating pump is a positive displacement pump where a certain volume of liquid is collected in an enclosed volume and is discharged using pressure to the required application.

Slip:

Slip of a pump is defined as the difference between the theoretical discharge and actual discharge of the pump. The actual discharge of a pump is less than the theoretical discharge due to leakage.

Mathematically,

slip = Qth- Qact

where,

Qth = Theoretical discharge

Qact = Actual discharge

Negative Slip:

Negative slip of a pump is defined as the difference between the actual discharge and theoretical discharge of the pump.

Mathematically,

Negative slip = Qact- Qth

Concept:

Mechanical Efficiency

It is the ratio of the useful hydraulic power transmitted to the fluid leaving the pump to the total power absorbed by the pump.

\(η_{mech}=\frac{Fluid~power}{Brake~power}=\frac{ρ gQh}{BP}\)

where, Q = discharge through pump, h = head

Calculation:

Given:

ηmech = 0.80, m = 80 kg/s, h = 30 m

We know that, from continuity equation, m = ρAV = ρQ

\(η_{mech}=\frac{ρ gmh}{ρ \times BP}=\frac{gmh}{BP}\)

\(0.80=\frac{9.81\times80\times30}{BP}\)

BP = 29430 W = 29.43 kW

Explanation:

Discharge through the reciprocating pump:

The discharge through a single acting reciprocating pump is given as

Q = Volume of water delivered in one revolution × number of revolutions per second

\(Q = V \times \frac{N}{{60}}\)

\(Q = \left( {Area \times Length\;of\;stroke} \right) \times \frac{N}{{60}}\)

\(Q = \left( {A \times L} \right) \times \frac{N}{{60}}\)

\(Q = \frac{{ALN}}{{60}}\)

For a single acting reciprocating pump

\(Q = \frac{{ALN}}{{60}}\)

For a double acting reciprocating pump

\(Q = \frac{{2ALN}}{{60}}\)

where, A is a cross-sectional area of cylinder / piston. L is the stroke length of the piston and N is the rpm of the crank.

Explanation:

Air vessel:

• It is a closed chamber fitted on the suction as well as delivery side, near the pump cylinder to reduce the accelerating head.
• To reduce the acceleration head we need to reduce the length of the suction pipe and the length of the delivery pipe in which fluctuation of velocity occurs.
• This is done by fitting air vessels as close as possible.
• Thus between air vessel and cylinder only fluctuating velocity will occur. Below air vessel on the suction side and above air vessel on delivery side velocity will be constant.

Functions of air vessel:

1) On the suction side:

• Reduction of the possibility of separation of flow
• The pump can run at a higher speed.
• The length of the suction pipe below the air vessel can be increased.

2) On the delivery side:

• A constant rate of discharge can be ensured.
• Save power required to drive the pump (For single-acting pump, percentage work saved is 84.8% and for double-acting pumps the percent work save is 39.2%)

Explanation:

Reciprocating pump:

• A reciprocating pump is a positive displacement pump where a certain volume of liquid is collected in an enclosed volume and is discharged using pressure to the required application.

Slip:

• The slip of a pump is defined as the difference between the theoretical discharge and the actual discharge of the pump. The actual discharge of a pump is less than the theoretical discharge due to leakage.
• Mathematically,
• slip = Qth- Qact
• where, Qth = Theoretical discharge, Qact = Actual discharge

Negative Slip:

A negative slip of a pump is defined as the difference between the actual discharge and theoretical discharge of the pump.

Conditions negative slip is given as

• The delivery pipe is short.
• The suction pipe is long.
• The pump is running at high speed.
• Mathematically,
• Negative slip = Qact- Qth

Explanation:

Pumps

The hydraulic machines which convert the mechanical energy into hydraulic energy are called pumps.

There are basically 2 types of pumps.

Explanation:

• The hydraulic machines which convert the mechanical energy into hydraulic energy are called pumps.
• If the mechanical energy is converted into pressure energy by means of the centrifugal force acting on the fluid, the hydraulic machine is called a centrifugal pump.

Concept:

Reciprocating Pump: 

The hydraulic machines which convert the mechanical energy into hydraulic energy are called pumps. The mechanical energy is converted into hydraulic energy by sucking the liquid into a cylinder in which a piston is reciprocated (moving backward and forwards), which exerts the thrust on the liquid and increases its hydraulic energy, the pump is known as a reciprocating pump.

Classification of reciprocating pumps: 

It may be classified as:

1. According to the water being in contact with one side or both sides of the piston

• Single-acting pump
• Double-acting pump

2. According to the number of cylinders provided

• Single-cylinder pump
• Double-cylinder pump
• Triple-cylinder pump

Explanation:

• Single-acting pumps discharge on either the forward or return stroke of the piston or plunger; every cycle of the pump displaces only one volume of liquid.
• In double-acting pumps, the liquid is discharged on both the forward and return stroke of the piston. So that the flow is double in a double-acting reciprocating pump and compared to a single-acting reciprocating pump.

Explanation:

Centrifugal pump:

• Centrifugal pumps are classified as rotodynamic type of pumps in which a dynamic pressure is developed which enables the lifting of liquids from a lower to a higher level.
• The action of the centrifugal pump is just the reverse of radially inward flow reaction turbines (i.e. Radially outward flow) which take water from the tailrace and deliver it to the head race.
• The centrifugal pump works on the principle of forced vortex flow which means that when a certain mass of liquid is rotated by an external torque, the rise in pressure head of the rotating liquid takes place.
• The rise in pressure head at any point of the rotating liquid is proportional to the square of the tangential velocity of the liquid at that point.
• Thus at the outlet of the impeller, where the radius is greater, the rise in pressure head will be greater, and liquid will be discharged at the outlet with a high-pressure head.
• Due to this high-pressure head, the liquid can be lifted to a high level.
• Generally, a centrifugal pump works well within a head of 1 to 100 m and a discharge of 40 to 50 m3/s. whose efficiency is up to 90%. However, the efficiency of centrifugal pumps commonly used for lifting water from wells can vary is typically in the range of 60% to 70%.

​Hence option (2) is the correct answer.