GI Duct are pre-fabricated and longitudinally pre-assembled to a maximum length of 1.2m at the workshop as per the construction schedule enclosed. Preparation/formation of flanges for transverse joints are made at workshop.
GI Duct received at site as above shall be joined together on the floor, to form manageable lengths. Wherever branch take-off collars are to be fixed, suitable cut out shall be made in the ducts. The size of cut out shall be equal to the duct cross sectional area and secured using aluminium pop rivets and the joint between collar flange and duct surface shall be sealed with duct sealant.
Pre-insulated Ducting: Ducts are pre-fabricated in the workshop and longitudinally assembled to a maximum length of 4m. Preparation for the traverse joints including the fixing of the flanges/profiles as applicable as per the construction schedule is carried out at workshop.
HVAC GI Ducts received at site as above shall be joined together on the floor to form manageable lengths.Branch take-off collars are tap-in glued type and will have shoe configuration at the take-offs. Wherever branch take-offs are to be made, suitable cut out shall be made on the main duct with 45° angle cutter to form the 45° female part of the joint. The branch/take-offs with 45° male cut ends are secured to the main duct by the joining glue. The joint is sealed with duct sealant and finished with self-adhesive aluminium foil tape.
Installation Method for Horizontal GI Duct
The layout of duct to be installed shall be as per approved drawing. Position of duct supports shall be marked on the underside of the slab / structural member/vertical approved drawings.
Threaded rod of suitable size shall be fixed to the mechanical anchor fastener / clamps using proper lock nut. GI angle, cut to required size of duct (to have clearance of 50mm on either side) shall be fixed to the threaded rod suspension and locked in position by suitable nuts and washers.
Assembled, as above, ducts shall be lifted and shall be installed on trapeze. Pre-insulated ducts are joined either by glue in type male & female joints or with PVC H bayonet cleats for flanged joints as applicable as per the construction schedule. Duct sealant is applied at the male and female joint and finished by self-adhesive aluminum tape.
On laying the ducts as detailed above to form the required layout, the ducts shall be properly aligned and leveled to maintain B.O.D. and distances as per approved drawing.
Method for Installation of Riser / Shaft Duct
- GI Duct supports shall be taken at each floor / vertical wall as the case may be and shall be as per approved drawings. Successive ducts shall be installed starting from low level as the successive higher floors are constructed. The open end of the upper most ducts shall be sealed properly.
- The insulation of the flexible ducts shall be rolled upto 100mm from the edges and the flexible duct shall be slipped on to the collar fixed on the main duct and shall be secured firmly using G.I. Straps and clips. Then the insulation of flexible duct shall be rolled back and fixed firmly on to spigots and adjoining duct surface and finished with self-adhesive aluminium foil tape.
- Flexible ducts installed as above shall be supported using 25mm G.I. strip wound around the duct and suspended from slab if the flexible duct length exceeds 1.5 meter. Suitable plenum box as applicable shall be connected to main duct through pre-insulated flexible ducts.
- Manual volume control dampers as approved shall be fixed in the ducting system wherever mentioned in the drawing.
- Fire damper shall be installed as per approved drawing / manufacturer installation details.
- Access doors shall be provided for fire dampers wherever applicable.
- Diffusers plenum/droppers shall be leveled properly to suit false ceiling.
- The ducts are identified (service wise) as per approved identification labels (directional arrows).
- After the duct installation QC shall inspect the complete installation and offer the same for consultant’s inspection.
- On fixation of final fix items like grilles / diffusers etc, consultant’s engineer shall be invited for final inspection and certification.