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Discussion in 'المنتدى التعليمي' started by mannan, 10/10/17.

  1. mannan

    mannan Administrator Staff Member



    الحمد لله والصلاة والسلام على رسول الله وعلى آله وصحبه أجمعين



    A. All ducting must be made of galvanized steel sheet to ASTM A525
    lock-forming quality, having zinc coating of 275gm/M² for both sides
    in accordance with ASTM A90 and of tensile strength 28/33 tons per square inch

    B. All ducting must be made as indicated in the installation drawings and
    successful tenderer must check the installation and building before
    hand and ensure that the existing structures, etc., must not come in
    the way of ducting at time of installation
    Dimensions of ducting can be altered by the contractor with the prior
    approval of concerned Engineer without altering permissible airflow rates

    C. All ducting must be suitably stiffened to avoid vibration, sagging and
    running effects due to airflow. All ducting must be made airtight

    D. Gauges of G.I sheeting, type of joints, bracing, etc., used for the
    manufacture ducting must be as shown below

    E. The throat radius of bend must not exceed half the width of associated
    side of the duct and where it is not possible to comply with this duct turning
    vane must be used along with the right angle bends
    The duct turning vanes must be spaced in such a way that the speed
    ratio of each of the individual elbows must be around 6:1

    Maximum Side inches US Standard Gauge
    Transverse Joints and Bracing 154BUp to 12" 24
    ¾” pocket or slip joint at 8 ft. centres 13 – 18” 24
    1” pocket joint at 4 Ft. centers with cross breaking 19 – 30” 22
    1” pocket joint at 4 Ft. centers with cross breaking 31 - 42” 22
    1½” pocket joint at 4 Ft. centers with cross breaking and ½ x ½ x 1/8
    angle with girth at 8 ft. centres bolted to the pocket joint 43 – 54” 20
    1½” pocket joint at 4 Ft. centers with cross breaking and 1½ x 1½ x 3/16
    angle with girth at 8 ft. centres bolted to the pocket joints 55 – 72” 20
    1½” pocket joint at 4 Ft. centers with cross breaking and 1½ x 1½ x 3/16
    angle with girth at 4 ft. centres bolted to the pocket joints 73 to Up 18
    2½” x 1½” x 3/16 angles at 4 Ft. centers bolted to the duct with 3/8
    bolts at 1½ centers and fastened together with 3/8” bolts at 2 centres
    with rubber gasket between the 2 angles and cross breaking


    50 mm Slip Joint or Draw Band is acceptable through 1500 mm size
    Slip or Draw Band Joint Flanged Joint

    All tees, Bends and Elbows must be constructed with radius
    of not less than 1½ times diameter of duct on centerline
    Where not possible and where rectangular elbows are used
    aerofoil-turning vanes must be provided
    Transformation of duct sizes must be gradual, not exceeding
    15 degrees divergence and 30 degrees convergence
    Round duct fittings must be of welded type construction
    For ducts of diameter up to and including 300-mm. diameter
    one-piece smooth 90 deg. elbows must be used. Over 300-mm dia
    they must be 5 piece welded

    Turning Vanes

    must be fabricated in accordance with SMACNA Standards
    Turning vanes must be as follows
    Factory or site-fabricated using factory-fabricated vane spacing rails
    Turning vanes must be provided in all square elbows, take-off or
    extension collars to supply outlets and tap-in branch take-off connections
    Turning vanes must be reinforced by rods or of sectional construction
    Turning vane arrangements and thickness must be as shown
    153 B SINGLE 152 B VANE 151 B SCHEDULE Type Space between Vanes
    Radius Gauge Small Large
    1½” 3” 2” 4½” 24 22

    Volume Control Damper

    Volume control dampers must be provided in ductwork to regulate and
    balance air systems, since dampers on the air inlet and outlet must be
    used only for fine secondary regulating or balancing
    The damper must be fabricated in accordance with
    SMACNA Duct Construction Standards

    Single blade dampers must be used for damper widths up to 300 mm
    provided that there is sufficient length of straight duct after the
    damper to ensure equal flow before the next take-off or outlet
    Where the damper width is over 300 mm. multi -blade dampers must be used
    Multi blade dampers styles must be generally parallel blade for two-position
    operation and opposed blades for modulating position
    The blades must be constructed of galvanized sheet, suitably
    stiffened by forming or other method, and assembled in prime coated
    or galvanized channel frame with suitable hardware
    The bearings must be of bronze or oil impregnated nylon

    Looking and indicating quadrant regulator must be provided for each damper
    The indicating quadrant must be clearly marked to indicate
    close, ¼, ½ , ¾ and open positions
    On insulated ducts, quadrant regulators must be mounted
    on stand off mounting brackets or bases

    For motor operated damper, the motor-operator must be electric type

    Fire Dampers

    must be fabricated in accordance with NFPA 90A
    and UL 555 or equivalent and must be
    1• To be provided in ducts and openings in shafts, floor
    firewalls, fire partitions and the rated ceilings

    2• In horizontal ducts, fire dampers may be single or of a multi
    blade type. In vertical ducts only single blade type must be used

    3• Galvanized sheet metal housing to be provided with angle flanges on both sides

    4• The damper must be of 1.6 mm thick sheet steel or steel/mineral
    fiber/steel sandwich of equivalent fire resistance, thermally released

    5• Fire dampers must be equipped with fuse plug, positioning levers
    fittings and position indicator accessible from outside

    Grilles and Registers

    They must be furnished with sponge rubber gaskets or foam
    tape behind the frame to eliminate air leakage and with nylon
    bushings or PVC at the blades connection to the frame to eliminate
    corrosion and vibration. Free cross-sectional area must be at least 65 percent

    1- Supply air registers and grilles must have individually adjustable
    horizontal front blades and vertical rear blades

    2- Supply air register must be equipped with key
    operated, opposed blade volume control damper

    3- Return and exhaust air registers and grilles must have
    fixed single deflection blades set at an angle of 35 degrees

    4- Return and exhaust air registers must be equipped with
    key operated, opposed blade volume control damper

    5- All opposed blade volume control dampers must be polyester
    powder coated ovens taken with black colour finish

    Jet Diffusers

    must have manual discharge pattern adjustment from the
    front or back of diffuser, the outer flange of the jet diffuser
    to be made of aluminium, the inner core and rings to be made
    of mild steel construction, to be coloured by
    electrostatic polyester powder coating finish

    Access Doors

    Airtight access doors with rubber linings must be installed in all ducts
    at fans, filters, heaters, fire dampers and volume dampers for inspection
    cleaning and maintenance purposes

    The opening in the ductwork must be properly stiffened at the edges
    with frames riveted or welded to the duct
    The access door must be
    All Access Doors mounted on insulated ducts must be
    of sandwich type, having the same insulation thickness
    as that of the duct, with Cam Lock handles

    Maximum Size(mm) No. of Hinges No. of Handles Door Gauge Back Frame
    12” x 12” 2 1 26 26 24 16” x 20” 2 2 24 26 22 24” x 24” 3 2 22 26 22

    Flexible Connections

    Flexible connections must be fitted on all suction and discharge
    connections of fans and air conditioning units, for preventing
    transmission of vibration through the ducts to occupied spaces

    Flexible connections must be made from flame proof, factory
    fabricated from chemically impregnated canvas
    Connections must fit closely and be secured in an airtight
    fashion to duct work, fans and apparatus by means of angle
    iron or flat iron frames. The unclamped section of the flexible
    connection between the apparatus and the ductwork must be
    not less than 150 mm. in length. Flexible connections must not be painted

    Supports and Hangers

    Installation of supports and hangers must be

    Supports and hangers must be attached only to structural
    framing members and concrete slabs. They must not be anchored
    to metal decking unless a means is provided and approved for
    preventing the anchor from puncturing the metal decking

    Supports must generally be made from galvanized steel sections
    and where heavy items of equipment occur within ductwork
    additional support must be provided as necessary

    Duct work hung from inserts or from clip angles must
    be secured with expansion bolts in shear.

    Supports for horizontal ducts must be

    RECTANGULAR DUCT Length of Longer Side (mm) Drop Rod Diameter (mm)
    Bearing Member (mm) 155BMaximum Spacing ( inch) 156 B up to 12” 8
    20 x 3 Flat 120” 157B Over 12” up to 24” 8 25 x 25 x 3 angle 120”
    Over 24” up to 40” 10 40 x 40 x 4 angle 100” Over 45” up to 64” 10
    50 x 50 x 5 angle 100” Over 64” 15 75 x 75 x 6 angle 100”

    Design of supports for vertical ducts will be dictated by site
    conditions and spacing may be greater than for horizontal ducts

    Supports for vertical ducts must be angles and
    channels made of galvanized or painted black steel

    Vertical duct must be fastened with a minimum
    of 2 supports at each floor

    في أمان الله



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