Pumps and Working Principle
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Questions and Answers

What is a pump?

A pump is a mechanical device that is used to provide energy to a fluid to move it from one place to another.

Which of these is NOT a classification of pumps based on method of displacement?

  • Reciprocating pumps
  • Positive displacement pumps
  • Rotodynamic pumps
  • Centrifugal pumps (correct)

    • Positive displacement pumps apply direct pressure to the fluid.

    True

    How do rotodynamic pumps function?

    <p>Rotodynamic pumps increase the velocity of the liquid with the help of a rotating vane impeller, producing head and flow.</p> Signup and view all the answers

    Which type of positive displacement pump uses oscillating pistons, plungers, or membranes?

    <p>Reciprocating pumps</p> Signup and view all the answers

    Diaphragm pumps are commonly used to handle hazardous or toxic fluids.

    <p>True</p> Signup and view all the answers

    What are gear pumps, lobe pumps, and screw pumps collectively known as?

    <p>Rotary pumps</p> Signup and view all the answers

    Rotary pumps require check valves for fluid movement in one direction.

    <p>False</p> Signup and view all the answers

    What type of fluid are gear pumps, lobe pumps, and screw pumps best suited for?

    <p>Viscous fluids</p> Signup and view all the answers

    Which pump type is known for its ability to handle grit and slurry?

    <p>Centrifugal pumps</p> Signup and view all the answers

    Reciprocating pumps typically require higher speeds and result in a high discharge rate compared to centrifugal pumps.

    <p>False</p> Signup and view all the answers

    What is the main component in a centrifugal pump that rotates to generate fluid movement?

    <p>Impeller</p> Signup and view all the answers

    The casing of a centrifugal pump is a non-airtight chamber surrounding the impeller.

    <p>False</p> Signup and view all the answers

    What is the purpose of the volute in a centrifugal pump?

    <p>The volute gradually increases the area of flow from the impeller outlet towards the delivery pipe.</p> Signup and view all the answers

    Which of these is NOT a type of head commonly discussed in the context of centrifugal pumps?

    <p>Pressure head</p> Signup and view all the answers

    What is the manometric head (Hm) in a centrifugal pump?

    <p>The manometric head represents the total head against which the pump has to work.</p> Signup and view all the answers

    The pump overall efficiency is determined by comparing the power output of the pump to the power input to the pump.

    <p>True</p> Signup and view all the answers

    What is the term for the pressure head created by the weight of lifted water in a centrifugal pump?

    <p>Water horsepower</p> Signup and view all the answers

    The power input to a centrifugal pump is determined by the power supplied by the electric motor.

    <p>True</p> Signup and view all the answers

    What does the specific speed (N_s) of a centrifugal pump represent?

    <p>The specific speed is a dimensionless parameter that represents the ratio of impeller speed to the flow rate and head produced by the pump.</p> Signup and view all the answers

    The head coefficient in a centrifugal pump relates the head to the pump's diameter and impeller speed.

    <p>True</p> Signup and view all the answers

    What is the significance of the power coefficient in a centrifugal pump?

    <p>The power coefficient indicates the relationship between the power required by the pump and its operating conditions, including diameter, impeller speed, and fluid properties.</p> Signup and view all the answers

    The capacity coefficient relates the flow rate to the pump's diameter and impeller speed.

    <p>True</p> Signup and view all the answers

    In the main characteristic curves of a centrifugal pump, what does the curve for P(Q AND H CONSTANTS) represent?

    <p>The relationship between power input and head at constant discharge rate</p> Signup and view all the answers

    The curve for H(Q = CONSTANT) represents the relationship between head and speed at a constant discharge rate.

    <p>True</p> Signup and view all the answers

    What does the curve for Q(H = CONSTANT) show in the main characteristic curves of a centrifugal pump?

    <p>This curve displays the relationship between discharge rate and speed at a constant head.</p> Signup and view all the answers

    The pump performance curves for centrifugal pumps are typically plotted against the discharge rate (Q).

    <p>True</p> Signup and view all the answers

    When a centrifugal pump is filled with gas or vapor instead of liquid, what condition occurs causing it to malfunction?

    <p>Vapor lock</p> Signup and view all the answers

    Even though the head developed by a vapor-filled pump is the same as a liquid-filled pump, the pressure is significantly lower due to the lower density of gases.

    <p>True</p> Signup and view all the answers

    What is the process of filling a centrifugal pump with liquid prior to operation called?

    <p>Priming</p> Signup and view all the answers

    Priming is essential for all types of pumps, including positive displacement pumps.

    <p>False</p> Signup and view all the answers

    What is the main purpose of placing a centrifugal below the liquid level?

    <p>To enable self-priming.</p> Signup and view all the answers

    Priming involves keeping the impeller submerged in liquid without any air pockets during the initial startup.

    <p>True</p> Signup and view all the answers

    What is cavitation in a centrifugal pump?

    <p>Cavitation occurs when the pressure in a centrifugal pump drops below the vapor pressure of the liquid, leading to the formation of vapor bubbles that collapse violently, causing damage and noise.</p> Signup and view all the answers

    Higher liquid temperatures increase the likelihood of cavitation in a centrifugal pump.

    <p>True</p> Signup and view all the answers

    What happens when the vapor bubbles generated during cavitation collapse?

    <p>The collapsing vapor bubbles create local shock waves that can damage the pump's internal components.</p> Signup and view all the answers

    Cavitation can contribute to excessive noise and vibrations in centrifugal pumps.

    <p>True</p> Signup and view all the answers

    What is the maximum suction lift (height) that can be tolerated to avoid cavitation in a centrifugal pump?

    <p>The maximum suction lift is determined as hs = Ha - H_v - (vs^2 / 2g) - h_fs, where hs is the maximum allowable suction height, Ha is the atmospheric pressure head, H_v is the vapor pressure head, vs is velocity at the free surface, and h_fs is the head loss in the suction pipe. It ensures that the pressure at the pump inlet is sufficient to avoid cavitation.</p> Signup and view all the answers

    The NPSHR is the minimum absolute head at the pump intake that is required to prevent cavitation.

    <p>True</p> Signup and view all the answers

    What is the NPSHA, and how does it relate to cavitation?

    <p>NPSHA is the available net positive suction head, representing the actual head available at the pump inlet. A higher NPSHA reduces the likelihood of cavitation, while a lower NPSHA increases the risk.</p> Signup and view all the answers

    The NPSHR typically increases with flow rate (Q), while NPSHA decreases with Q.

    <p>True</p> Signup and view all the answers

    The Thoma's cavitation factor (σ) is a dimensionless parameter that is typically smaller than the critical cavitation factor (σ_c) for proper pump operation.

    <p>True</p> Signup and view all the answers

    Study Notes

    Pumps and Working Principle

    • A pump is a mechanical device that provides energy to a fluid, moving it from one location to another.
    • Pumps raise, transfer, deliver, or compress fluids, or attenuate gases, often using suction or pressure, or both.
    • Pumps increase pressure, kinetic, and/or potential energy of the fluid by converting mechanical energy.

    Classification of Pumps

    • Pumps are classified based on their displacement method.

    1. Positive Displacement Pumps

    • These pumps move a fixed amount of fluid by trapping it and then moving it to the discharge pipe.
    • The volume flow rate is fixed per operating cycle.
    • They apply direct pressure to the fluid.

    2. Rotodynamic Pumps

    • These pumps increase the velocity of the liquid using a rotating impeller.
    • Creates head and flow by increasing the liquid's velocity.
    • Uses torque to generate rotation.
    • Impart kinetic energy through angular momentum of the impeller.

    Types of Positive Displacement Pumps

    • Reciprocating pumps: Use pistons or plungers to move fluids.

      • Can be single-acting or double-acting, with discharge on one or both strokes.

    • Diaphragm pumps: Use a flexible diaphragm to move fluids.

      • Suitable for handling hazardous or toxic fluids in small amounts at moderate pressure.

    • Rotary pumps: Move fluids using rotating parts like gears, lobes, or screws.

      • Gears, lobes, and screw pumps are suitable for viscous fluids and do not usually require check valves due to unidirectional fluid movement.

    Centrifugal Pumps

    • These pumps increase fluid energy by imparting angular momentum to the liquid, converting it into pressure head in the volute.
    • High velocity areas are present close to the impeller. Lowest pressure areas occur where velocity is greatest.

    Components of a Centrifugal Pump

    • Impeller: The rotor with curved vanes or blades, driven by a motor.
    • Casing: An enclosed chamber surrounding the impeller, increasing the flow area (volute) from the impeller outlet to the delivery pipe.
    • Suction pipe: Connects the impeller eye to the liquid source (sump).
    • Delivery pipe: Connects the pump outlet to the required height.

    Maximum Suction Lift (hs)

    • Calculations involve Bernoulli's equation to ensure that the pressure at the pump inlet is above the vapor pressure to avoid cavitation.
    • Cavitation is the formation and collapse of vapor bubbles, damaging components.

    NPSH (Net Positive Suction Head)

    • It is the minimum pressure above the liquid's vapor pressure needed to prevent cavitation.
    • NPSH is affected by vapor pressure, suction head losses, and fluid velocity.
    • Higher NPSH values are required for larger pumps, faster impeller speeds, and higher discharge pressures.

    Centrifugal Pump Characteristic Curves

    • Plotting curves of Head (H), Power (P), Discharge (Q), and Pump Efficiency (η) against flow rate (Q) provide a graphical representation to determine optimal operating conditions.

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    Pumps PDF

    Description

    Explore the mechanics of pumps, including their functions and classifications. This quiz covers positive displacement and rotodynamic pumps, detailing how they operate and the principles behind fluid movement. Test your understanding of the energy conversion processes involved in pump mechanics.

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