PACKAGE : I Bid Document VOLUME : II - Public Health Engineering

21.18 Filter floor & under drainage system.
In the conceptual design nozzles and suspended floor arrangement has been
proposed. The filter media shall be supported on suspended floor fitted with long
stemmed plastic floor nozzles and designed to pass the air and water required for
the reverse flow cleaning and to exclude the media from the filter base and outlet
systems. The filter shall be manufactured in precast concrete segments with
accurately set screwed thread plastic nozzles fixing sleeves. Nozzles shall be evenly
spread over the full floor area with a concentration of at least 50 per m . During
installation of any floor, all nozzle socket shall be plugged until nozzle fitting
commences. The contractor can also propose the piped under drain system. In the
event of adopting similar system, the contractor shall provide reinforced
concrete flooring with slots in each section to filter to accommodate manifold, or he
may provide concrete channel in each section to collect and convey pure
water/backwash water and air flow/ to the under drain laterals.
21.19 For piped under drains.
Complete hydraulic calculation for laterals orifices, and manifolds, and the
tolerance ratios of their areas with the filter area, also the inter-relations of the areas
of all the components of under drain systems.
The contractor shall clearly indicate at the tender stage the arrangements he
proposes to connect the laterals with the manifold and backwash water and air
arrangement.
21.20 Filter cleansing.
Filter cleansing shall be by (upward) reverse flows of air and water. Systems
employing separate air and water washing are envisaged. Both sections (halves) of a
filter unit shall be washed at the same time. The air supply shall be taken from one
of the air blowers and the water supply from over head system proposed.
Cleansing and sequence :
The Contractor shall fully .Justify in his tender submission. the filter cleansing
system for the contractor's particular version of the conceptual design. The
contractor shall include consideration of water loss, design sequence and timings,
rise rates, the water temperature, surface travel distance for wash water, case of
operation timings as duration's of the wash period etc.
DTS : Detailed Tender Specification. Page 252