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An introduction to Centrifugal Pumps

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    الصورة الرمزية م.مجدي عليان
    م.مجدي عليان
    م.مجدي عليان غير متواجد حالياً

    عضو تحرير المجلة

    تاريخ التسجيل: Jan 2005
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    An introduction to Centrifugal Pumps

    A centrifugal pump converts the input power to kinetic energy in the liquid by accelerating the liquid by a revolving device - an impeller. The most common type is the volute pump. Fluid enters the pump through the eye of the impeller which rotates at high speed. The fluid is accelerated radially outward from the pump chasing. A vacuum is created at the impellers eye that continuously draws more fluid into the pump.

    The energy created by the pump is kinetic energy according the Bernoulli Equation. The energy transferred to the liquid corresponds to the velocity at the edge or vane tip of the impeller. The faster the impeller revolves or the bigger the impeller is, the higher will the velocity of the liquid energy transferred to the liquid be. This is described by the Affinity Laws.

    Pressure and Head
    If the discharge of a centrifugal pump is pointed straight up into the air the fluid will pumped to a certain height - or head - called the shut off head. This maximum head is mainly determined by the outside diameter of the pump's impeller and the speed of the rotating shaft. The head will change as the capacity of the pump is altered.

    The kinetic energy of a liquid coming out of an impeller is obstructed by creating a resistance in the flow. The first resistance is created by the pump casing which catches the liquid and slows it down. When the liquid slows down the kinetic energy is converted to pressure energy.

    it is the resistance to the pump's flow that is read on a pressure gauge attached to the discharge line
    A pump does not create pressure, it only creates flow. Pressure is a measurement of the resistance to flow.

    In Newtonian fluids (non-viscous liquids like water or gasoline) the term head is used to measure the kinetic energy which a pump creates. Head is a measurement of the height of the liquid column the pump creates from the kinetic energy the pump gives to the liquid.

    the main reason for using head instead of pressure to measure a centrifugal pump's energy is that the pressure from a pump will change if the specific gravity (weight) of the liquid changes, but the head will not
    The pump's performance on any Newtonian fluid can always be described by using the term head.

    Different Types of Pump Head
    Total Static Head - Total head when the pump is not running
    Total Dynamic Head (Total System Head) - Total head when the pump is running
    Static Suction Head - Head on the suction side, with pump off, if the head is higher than the pump impeller
    Static Suction Lift - Head on the suction side, with pump off, if the head is lower than the pump impeller
    Static Discharge Head - Head on discharge side of pump with the pump off
    Dynamic Suction Head/Lift - Head on suction side of pump with pump on
    Dynamic Discharge Head - Head on discharge side of pump with pump on
    The head is measured in either feet or meters and can be converted to common units for pressure as psi or bar.

    it is important to understand that the pump will pump all fluids to the same height if the shaft is turning at the same rpm
    The only difference between the fluids is the amount of power it takes to get the shaft to the proper rpm. The higher the specific gravity of the fluid the more power is required.

    Centrifugal Pumps are "constant head machines"
    Note that the latter is not a constant pressure machine, since pressure is a function of head and density. The head is constant, even if the density (and therefore pressure) changes.

    The head of a pump in metric units can be expressed in metric units as:

    h = (p2 - p1)/(ρ g) + v22/(2 g) (1)

    where

    h = total head developed (m)

    p2 = pressure at outlet (N/m2)

    p1 = pressure at inlet (N/m2)

    ρ = density (kg/m3)

    g = acceleration of gravity (9,81) m/s2

    v2 = velocity at the outlet (m/s)

    Head described in simple terms

    a pump's vertical discharge "pressure-head" is the vertical lift in height - usually measured in feet or m of water - at which a pump can no longer exert enough pressure to move water. At this point, the pump may be said to have reached its "shut-off" head pressure. In the flow curve chart for a pump the "shut-off head" is the point on the graph where the flow rate is zero

  2. [2]
    م.مجدي عليان
    م.مجدي عليان غير متواجد حالياً
    عضو تحرير المجلة
    الصورة الرمزية م.مجدي عليان


    تاريخ التسجيل: Jan 2005
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    Thumbs up centrifugal pumps standards

    Some commonly used centrifugal pumps standards

    ANSI/API 610-1995 - Centrifugal Pumps for General Refinery Service - Covers the minimum requirements for centrifugal pumps, including pumps running in reverse as hydraulic power recovery turbines, for use in petroleum, heavy duty chemicals, and gas industry services. The pump types covered by this standard can be broadly classified as overhung, between bearings, and vertically suspended.
    DIN EN ISO 5199 - Technical specifications for centrifugal pumps
    ASME B73.1-2001 - Specification for Horizontal End Suction Centrifugal Pumps for Chemical Process - This standard covers centrifugal pumps of horizontal, end suction single stage, centerline discharge design. This Standard includes dimensional interchangeability requirements and certain design features to facilitate installation and maintenance. It is the intent of this Standard that pumps of the same standard dimension designation from all sources of supply shall be interchangeable with respect to mounting dimensions, size and location of suction and discharge nozzles, input shafts, baseplates, and foundation bolt holes
    ASME B73.2-2003 - Specifications for Vertical In-Line Centrifugal Pumps for Chemical Process
    BS 5257:1975 - Specification for horizontal end-suction centrifugal pumps (16 bar) - Principal dimensions and nominal duty point. Dimensions for seal cavities and base plate installations.

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    Best Regards
    Majdi N. Elyyan

  3. [3]
    م.مجدي عليان
    م.مجدي عليان غير متواجد حالياً
    عضو تحرير المجلة
    الصورة الرمزية م.مجدي عليان


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    Thumbs up centrifugal pump

    When a viscous fluid is handled by a centrifugal pump

    brake horsepower requirement increases
    the head generated is reduced
    capacity is reduced
    efficiency of pump is reduced and the Best Efficiency Point - BEP - is moved

    The head, flow and capacity at other viscosities than used in the original documentation can be modifying with coefficients.

    Flow
    qv= cq q (1)

    where

    qv = flow compensated for viscosity (m3/h, gpm)

    cq = viscosity flow coefficient

    q = original flow according pump curve (m3/h, gpm)

    Head
    hv= ch h (1)

    where

    hv = head compensated for viscosity (m, ft)

    ch = viscosity head coefficient

    h = original head according pump curve (m, ft)

    Efficiency
    μv= cμ μ (1)

    where

    μv = effciency compensated for viscosity

    cμ = viscosity efficiency coefficient

    μ = original efficiency according pump curve

    Power - SI units
    Pv= qv hv ρv g / (3.6 106 μv) (1)

    where

    Pv = power compensated for viscosity (kW)

    ρv = density of viscous fluid (kg/m3)

    g = acceleration of gravity (9.81 m/s2)

    Power - Imperial units
    Pv= qv hv SG / (3960 μv) (1)

    where

    Pv = power compensated for viscosity (bhp)

    SG = specific gravity of viscous fluid

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    Best Regards
    Majdi N. Elyyan

  4. [4]
    م.مجدي عليان
    م.مجدي عليان غير متواجد حالياً
    عضو تحرير المجلة
    الصورة الرمزية م.مجدي عليان


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    Thumbs up Classifications of Pumps

    Centrifugal Pumps (Roto-dynamic pumps)
    The centrifugal or roto-dynamic pump produce a head and a flow by increasing the velocity of the liquid through the machine with the help of a rotating vane impeller. Centrifugal pumps include radial, axial and mixed flow units.

    Centrifugal pumps can further be classified as

    end suction pumps
    in-line pumps
    double suction pumps
    vertical multistage pumps
    horizontal multistage pumps
    submersible pumps
    self-priming pumps
    axial-flow pumps
    regenerative pumps
    Positive Displacement Pumps
    The positive displacement pump operates by alternating of filling a cavity and then displacing a given volume of liquid. The positive displacement pump delivers a constant volume of liquid for each cycle against varying discharge pressure or head.

    The positive displacement pump can be classified as:

    Reciprocating pumps - piston, plunger and diaphragm
    Power pumps
    Steam pumps
    Rotary pumps - gear, lobe, screw, vane, regenerative (peripheral) and progressive cavity
    Selecting between Centrifugal or Positive Displacement Pumps
    Selecting between a Centrifugal Pump or a Positive Displacement Pump is not always straight forward.

    Flow Rate and Pressure Head
    The two types of pumps behave very differently regarding pressure head and flow rate:

    The Centrifugal Pump has varying flow depending on the system pressure or head
    The Positive Displacement Pump has more or less a constant flow regardless of the system pressure or head. Positive Displacement pumps generally gives more pressure than Centrifugal Pump's.
    Capacity and Viscosity
    Another major difference between the pump types is the effect of viscosity on the capacity:

    In the Centrifugal Pump the flow is reduced when the viscosity is increased
    In the Positive Displacement Pump the flow is increased when viscosity is increased
    Liquids with high viscosity fills the clearances of a Positive Displacement Pump causing a higher volumetric efficiency and a Positive Displacement Pump is better suited for high viscosity applications. A Centrifugal Pump becomes very inefficient at even modest viscosity.

    Mechanical Efficiency
    The pumps behaves different considering mechanical efficiency as well.

    Changing the system pressure or head has little or no effect on the flow rate in the Positive Displacement Pump
    Changing the system pressure or head has a dramatic effect on the flow rate in the Centrifugal Pump
    Net Positive Suction Head - NPSH
    Another consideration is the Net Positive Suction Head NPSH.

    In a Centrifugal Pump, NPSH varies as a function of flow determined by pressure
    In a Positive Displacement Pump, NPSH varies as a function of flow determined by speed. Reducing the speed of the Positive Displacement Pump pump, reduces the NPSH

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    Best Regards
    Majdi N. Elyyan

  5. [5]
    م.مجدي عليان
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    عضو تحرير المجلة
    الصورة الرمزية م.مجدي عليان


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    Best Regards
    Majdi N. Elyyan

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    Eng-Maher
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    الحمد لله

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    احمد ابوعبيده
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  10. [10]
    anarab
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    ممكن من فضلكم اعرف مراحل تصنيع لا shaft فى ال centrifugal pump ؟
    و عمليات التشغيل التى تجرى على الshaft من خراطة و تجليخ........الخ

    و درجة نعومة الshaft النهائية.

    و جزاكم الله خيرا

    فى انتظار ردودكم.

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