Sistema Hidráulico

Suction Well, Suction Mains and Intake Structure A- Suction Mains and Suction Well

Each low lift pump shall have a separate suction main which shall be formed in ductile iron pipes of a dia. as indicated in Basic Data with strainer. The suction well shall be made of reinforced concrete 1:1½:3 with sulphate resisting cement and shall be divided into two equal compartments for independent operation. The dimensions of each compartment shall be according to Basic Data excluding inlet and outlet compartment.

The well shall be closed at bottom and fed by channel or ductile iron pipes. The inlet to the feed channel or pipes shall be protected by coarse screen bar of spacing not more than 100mm with manual racking arm include at 45° and fixed to concrete head walls with aprons and with concrete step for ease of maintenance. The inlets and outlets to the well shall be fitted with penstocks operated from a platform at the top of the well. The top of the well shall be 75cm above the reformed ground level or the highest water level which is higher, and invert of the well shall be 1.5m below lowest low water level in the river. To facilitate the maintenance of inlets a concrete stair of 1m, wide shall be made on the river bank towards the inlets. The mains between the well and the pump and filter house shall be laid at true rising grade not less than 1/200 and shall be bedded through their lengths in concrete 1:2½:5 mixture of 15cm thick and 1m base width.

The base of the well shall be sloped towards one end and a submersible pump with non-clogging impeller with a suitable capacity shall be provided to pump the settled silt when required for each compartment. External and internal steel ladders with extended hand holds and walkway with handrails around the section well shall be provided. The foot valves to the suction pipes shall be free connecting with rubber seating to the doors and fitted with galvanized steel strainers. The contractor shall be responsible for supplying all materials required to carry out the work. An arrangement shall be made to flush the strainers, feeding pipe mains and the well from the delivery mains of the high lift pumps and for this purpose a bypass from the delivery main to the feeding pipes shall be provided. The pipe dia. shall be not less than 150mm.

An outlet not less than 75mm with ball valve and flexible hose not less than 10m long shall be provided for cleaning the well. All the above pipes where laid within the ground shall be bolted gland ductile iron pipe. When the pipes are laid above the ground or in the steel structure, they

shall be flanged ductile iron pipes. Pipes with Tyton joints are not acceptable. The Contractor shall make arrangements to direct the water in the river towards the project by making diversions in the current of the water if required, and rip raping the embankment for a distance of 200m along the project area.

B- Suction Mains

Each low lift pump shall have a separate suction formed in flexible jointed pipes to be used conforming to BSS 4772 and ISO 2531kq. The lining of these pipes shall be the same as specified for the filtered water rising mains.

The inlet to the suction mains shall be located at the depth of water in the river at lowest low water permits a depth of not less than 0.6m above the top of the strainer. The mains shall be laid on a true rising grade of not less than 1/200 and shall be bedded throughout their length in 1:2½:5 concrete of 15cm thick and 1.2m width. The excavation of the pipe trench extending from the pump house to a point where the depth of cover has become reduced at 0.9m shall be carried to a depth of 0.3m below the level of the bottom of the pipes.

The pipes throughout this section shall be supported in the first instance on brick stools of 0.3m height at the bank of each joint. On completion of the laying and jointing of this section the pipes exclusive of the joints shall be semi-surrounded with concrete of 1:2½:5 mixture extending from the bottom of the trench to the horizontal diameter of the pipes. The pipes shall be central in this semi-surrounded which shall be of a base width of 1.2m for each. The further section of the mains extending from the terminus of the aforementioned suction to and inclusive of the suction head shall be supported and fixed at a suitable intervals not exceeding 2.5m from each other on and to an angle iron cross member to the required No. of rows of 10"x8" RSJ vertically driven hard and firm into the invert of the bed of river by a hydraulic monkey of suitable weight. For the purpose of pricing his tender the Contractor shall assume an embedded depth of the piles of 5m which shall be subject to a plus or minus adjustment in accordance with the rates set out by him in the Schedule of price. The tops of the piles shall be cut off flush with the top of pipes and an arrangement for a walkway leading the end of the suction mains shall be provided at a level 300mm above the highest high water level with handrails and galvanized open mesh grills from the embankment along the structure and around the bulkhead below. A substantial bulwark shall be provided to the suction head in safeguard against impingement by river craft. The height of this structure shall be 2m above the walkway level complete with a monorail and chain block for lifting the suction pipe and strainer. To preclude the sibling of the mains during periods of high silt content of the river provision shall be made for

backwashing of the mains from the pumping main to the spring loaded relief valve fitted to the other end of each main.

The discharge iron and valves shall be directed on the strainers at an angle. The foot valves shall be free acting with rubber seating to the doors and fitted with galvanized steel strainers. A conspicuous beacon cage and mask with suitable electrical intermittent red flushing lights shall be erected on the bank of the river at the point of the intersection of the suction mains for the precautionary purpose of warning the river craft of the location of the suction main extending within the river.

All the above pipes where laid within the ground shall be bolted gland ductile iron pipes. When the pipes are laid above the ground or on the steel structure they shall be flanged ductile iron pipe. Pipes with Tyton joints are not acceptable. The Contractor shall submit detailed design for the intake structure taking into consideration water velocity and all precautions from floating subjects during high water level and floating season, such as trees, dead animals, etc.

The clear distance between suction pipes on the intake structure shall be not less than 1.5m.

Puddle flanges shall be manufactured from the same material as the pipe work of which they form part and shall be to the approval of the Engineer.

All pipe work shall be color coded in accordance with BS 1710 to facilitate identification. Each valve shall have securely attached to it a large label identifying it by number and designating its function.

Standard special pipes and medium bends shall be used wherever possible in the layout.

C- INTAKE STRUCTURE

The intake structure shall be constructed according to drawing from reinforced concrete. The pump sump (Basement) shall be designed as a water tight structure in two compartments for independent operation during maintenance with bypass arrangement controlled by a 2 Nos. sluice valves.

The floor of the (Basement) shall be sloped to one corner with a sump to pump accumulated settled sludge to the river using duplicated submersible pumps. The Basement shall have access ladder and lighting.

The channel from river to the intake Basement shall be constructed according to the drawing from reinforced concrete the contractor is responsible to make a full hydraulic study to design the final shape of the channel.

Rip raping along the shoulder of the river for a distance of 50m from each side of the channel to protect the structure and to direct the

water to the channels. The Contractor shall make all necessary arrangement to minimize the problem of settling of the suspended maters at the channel bar during high turbidity seasons by using submerged scraping device.

Fence along the side of the intake channel shall be provided. Bar screens shall be hand raked type manufactured from rectangular section mild steel. Fixing lugs and bolts shall be manufactured from stainless steel provision for conversion to mechanical rack in the future is required.

The head loss across the screen shall be monitored by means of an (air purge) system. The equipment to be provided shall include dip tubes on both the upstream and downstream side of the screen, air compressor, mercury manometer, electrical probes, switches, contacts oelags and amplifiers, etc. required. The general design of the building shall be in accordance to clauses as specified.

CLAUSE NINETEEN