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موسوعة الهيدروليك وميكانيكا الموائع - Hydraulics & Fluid Mechanic

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    الصورة الرمزية مصطفى الوكيل
    مصطفى الوكيل
    مصطفى الوكيل غير متواجد حالياً

    عضو متميز

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    موسوعة الهيدروليك وميكانيكا الموائع - Hydraulics & Fluid Mechanic

    إخوانى المهندسين الميكانيكين الأعزاء ، قررت بعون الله أن أعمل موسوعات كاملة فى كل فروع الميكانيكا والباب مفتوح للجميع للمشاركات ، وستكون الموسوعات كالتالى :-


    • موسوعة الهيدروليك وميكانيكا الموائع - Hydraulics & Fluid Mechanic


    • موسوعة الضواغط - Compressors


    • موسوعة الطلمبات - Pumps


    • موسوعة السيارات والمحركات - Vehicles & Engines


    • موسوعة مكافحة الحريق - Fire Fighting


    • موسوعة خدمات المياة والسباكة - Water Services & Plumbing


    • موسوعة الصرف الصحي والمعالجة - Sewage & Treatment


    • موسوعة الديناميكا الحرارية وإنتقال الحرارة - Thermodynamics & Heat Transfer


    • موسوعة التصميم الميكانيكى والرسم - Mechanical Design & Drawing


    • موسوعة المعلومات العامة - General Knowledge


    • موسوعة التوربينات والغلايات - Turbines & Boilers


    • موسوعة الطيرات والمحركات النفاثة - Jet Engines


    • موسوعة التحكم الآلي - Automatic Control


    • موسوعة علم المعادن ومقاومة المواد - Metallurgy & Strength of Materials


    إذا رأيتم أن هناك موشوع فى الميكانيكا لم أكتبه أرجو الإقتراح وشكرا

    وعلى بركة الله نبدأ والله ولى التوفيق ،

    =========



  2. [2]
    مصطفى الوكيل
    مصطفى الوكيل غير متواجد حالياً
    عضو متميز
    الصورة الرمزية مصطفى الوكيل


    تاريخ التسجيل: Apr 2007
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    Hydraulic Basics

    Hydraulics is the science of transmitting force and/or motion through the medium of a confined liquid. In a hydraulic device, power is transmitted by pushing on a confined liquid

    Figure 1-1 shows a simple hydraulic device. The transfer of energy takes place because a quantity of liquid is subject to pressure. To operate liquid-powered systems, the operator should have a knowledge of the basic nature of liquids. This chapter covers the properties of

    liquids and how they act under different conditions

    1-1. Pressure and Force. Pressure is force exerted against a specific area (force per unit area) expressed in pounds per square inch (psi). Pressure can cause an expansion, or resistance to compression, of a fluid that is being squeezed. A fluid is any liquid or gas (vapor)

    Force is anything that tends to produce or modify (push or pull) motion and is expressed in pounds

    a. Pressure. An example of pressure is the air (gas) that fills an automobile tire. As a tire is inflated, more air is squeezed into it than it can hold. The air inside a tire resists the squeezing by pushing outward on the casing of the tire. The outward push of the air is pressure

    Equal pressure throughout a confined area is a characteristic of any pressurized fluid

    For example, in an inflated tire, the outward push of the air is uniform throughout. If it were not, a tire would be pushed into odd shapes because of its elasticity

    There is a major difference between a gas and a liquid. Liquids are slightly compressible (Figure 1-2). When a confined liquid is pushed on, pressure builds up. The pressure is still transmitted equally throughout the container

    The fluid's behavior makes it possible to transmit a push through pipes, around corners, and up and down. A hydraulic system uses a liquid because its near incompressibility makes the action instantaneous as long as the system is full of liquid




    Figure 1-1. Basic hydraulic device





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    مهندس إستشارى / مصطفى الوكيل
    M.E.P. Manager - ITCC Project, Riyadh
    Zuhair Fayez
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  3. [3]
    مصطفى الوكيل
    مصطفى الوكيل غير متواجد حالياً
    عضو متميز
    الصورة الرمزية مصطفى الوكيل


    تاريخ التسجيل: Apr 2007
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    Pressure can be created by squeezing or pushing on a confined fluid only if there is a resistance to flow. The two ways to push on a fluid are by the action of a mechanical pump or by the weight of the fluid. An example of pressure due to a fluid's weight would be in an ocean's depths. The water's weight creates the pressure, which increases or decreases, depending on the depth.

    By knowing the weight of a cubic foot of water, you can calculate the pressure at any depth. Figure 1-3 shows a column of water 1 foot square and 10 feet high, which equates to 10 cubic feet. (One cubic foot of water weighs 52.4 pounds.) The total weight of water in this column is 624 pounds. The weight at the bottom covers 1,445 square inches (1 square foot).

    Each square inch of the bottom is subject to 1/144 of the total weight, or 4.33 pounds. Thus, the pressure at this depth is 4.33 psi. You can also create an equal pressure of 4.33 psi in a liquid using the pump and figures shown in Figure 1-4, Before pressure, head was the only way to express pressure measurement. It was expressed as feet of water.

    Today, head is still the vertical distance between two levels in a fluid. In Figure 1-3, the head between the top and bottom of the water is 10 feet, which is equivalent to 4.33 psi. Therefore, each foot of water is equal to 0.433 psi.

    The earth has an atmosphere of air extending 50 miles up, and this air has weight. This air creates a head of pressure that is called atmospheric pressure.

    A column of air 1 square inch in cross section and the height of the atmosphere would weigh 14.7 pounds at sea level. Thus, the earth's atmospheric pressure is 14.7 psi at sea level. The role of atmospheric pressure in most hydraulic systems is significant.

    Figure 1-5, shows the interaction of hydraulic and atmospheric pressures under the three sets of conditions listed below:-

    (1) Diagram A. In the diagram, the tube is open at both ends. When it is placed in a liquid, the liquid will rise, inside and outside, in proportion to the amount of liquid displaced by the submerged tube wall.

    (2) Diagram B. In the diagram, ends of the tube are closed. When placed in a liquid, the liquid level in the tube is forced down because the air in the tube must occupy a space. Therefore, the liquid is displaced.

    The liquid level outside the tube rises in proportion to the volume of the cylinder wall and the volume of the trapped air below the original liquid level. The atmospheric pressure (14.7 psi) on the liquid outside the tube is not heavy enough to force the liquid inside the tube upward against the pressure of the trapped air, which is more than 14.7 psi.

    (3) Diagram C. In the diagram, the upper end of the tube is closed, but some of the air has been removed from this tube so that the pressure within the tube is less than 14.7 psi (a partial vacuum).

    A perfect vacuum would exist if all pressure within the tube could be eliminated, a condition that never happens. Because the liquid outside the tube is subject to full atmospheric pressure, the liquid is forced up into the tube to satisfy the vacuum. How far the liquid rises depends on the difference in air pressure between the trapped air and the atmosphere.

    b. Force. The relationship of force, pressure, and area is as follows:

    F = PA

    where :-

    F = force, in pounds
    P = pressure, in psi
    A = area, in square inches













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    مهندس إستشارى / مصطفى الوكيل
    M.E.P. Manager - ITCC Project, Riyadh
    Zuhair Fayez
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  4. [4]
    مصطفى الوكيل
    مصطفى الوكيل غير متواجد حالياً
    عضو متميز
    الصورة الرمزية مصطفى الوكيل


    تاريخ التسجيل: Apr 2007
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    Example:-

    Figure 1-6 shows a pressure of 50 psi being applied to an area of 100 square inches. The total force on the area is:-

    F = PA
    F = 50 x 100 = 5,000 pounds

    1-2. Pascal's Law.

    Blaise Pascal formulated the basic law of hydraulics in the mid 17th century.

    He discovered that pressure exerted on a fluid acts equally in all directions.

    His law states that pressure in a confined fluid is transmitted undiminished in every direction and acts
    with equal force on equal areas and at right angles to a container's walls.

    Figure 1-7 shows the apparatus that Pascal used to develop his law. It consisted of two connected cylinders of different diameters with a liquid trapped between them. Pascal found that the weight of a small piston will balance the weight of a larger piston as long as the piston’s areas are in proportion to the weights. In the small cylinder, a force of 100 pounds on a 1-square inch piston creates a pressure of 100 psi. According to Pascal's Law, this pressure is transmitted undiminished in every direction.

    In the larger cylinder, the 100 psi of pressure from the
    small cylinder is transmitted to an area of 5 square inches, which results in a force of 500 pounds on the second piston.

    The force has been multiplied 5 times—a mechanical advantage of 5 to 1. Using the same factors, you can
    determine the distance the pistons move.

    For example, if the small piston moves down 10
    inches, the larger piston will move up 2 inches. Use the following to determine the distance:

    D2 = (F1 x D1) / F2

    where:-

    F1 = force of the small piston, in pounds
    D1 = distance the small piston moves, in
    inches
    D2 = distance the larger piston moves, in
    inches
    F2 = force of the larger piston, in pounds

    Example: Determine D2

    D2 = (F1 X D1) / F2





    D2 = (100 X 10) / 500 = 2 In







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    مهندس إستشارى / مصطفى الوكيل
    M.E.P. Manager - ITCC Project, Riyadh
    Zuhair Fayez
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  5. [5]
    commander 15
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    عضو متميز


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    متابعك يا دكتور خطوة خطوة
    مع جزيل الشكر

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  6. [6]
    commander 15
    commander 15 غير متواجد حالياً
    عضو متميز


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    الموضوع مهم جدا واساس الهيدروليك
    واتمنى من المشرفين بتثبيته كي تتم الاستفادة منه بشكل اكبر
    ولكم جزيل الشكر

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  7. [7]
    شريف خليفه
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    عضو


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    بارك الله فيك
    وعندى اقتراح
    لماذا لا تضعهم ايضا فى ملفات وورد وتضعهم فى المرفقات بالموضوع
    وجزاك الله خيرا

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  8. [8]
    مصطفى الوكيل
    مصطفى الوكيل غير متواجد حالياً
    عضو متميز
    الصورة الرمزية مصطفى الوكيل


    تاريخ التسجيل: Apr 2007
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    شكرا على مروركم الكريم ولكن أحيانا يكون الكتاب عندى فأقوم بتصوير صفحاته بالكاميرا الخاصة بى وأنزله على الكمبيوتر كما أننى سأقوم بالتعليق كثيرا على الصفحات كما أننى أحب هذه الطريقة إذا سمحتم لى ولو أن عندى نسخة على شكل ملف فسوف أرفقه فورا
    وشكرا لمتابعتكم


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    M.E.P. Manager - ITCC Project, Riyadh
    Zuhair Fayez
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  9. [9]
    مصطفى الوكيل
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    عضو متميز
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    تاريخ التسجيل: Apr 2007
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    flow


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    تابعونى

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    مهندس إستشارى / مصطفى الوكيل
    M.E.P. Manager - ITCC Project, Riyadh
    Zuhair Fayez
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    مصطفى الوكيل
    مصطفى الوكيل غير متواجد حالياً
    عضو متميز
    الصورة الرمزية مصطفى الوكيل


    تاريخ التسجيل: Apr 2007
    المشاركات: 977
    Thumbs Up
    Received: 61
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    مهندس إستشارى / مصطفى الوكيل
    M.E.P. Manager - ITCC Project, Riyadh
    Zuhair Fayez
    ــــــــــــــــــــــــــــــــــــــ

  
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