Distribution System

Pipes : mains, sub mains, branches and Laterals
Valves : For controlling flow

Hydrants: For releasing water during fire breakouts

Meters : For measuring discharges

Pumps : For lifting water

Service reservoir : For storing the treated water & stabilizing pressures.

Importance : It involves 40 to 70% of the total cost of W.S. scheme. .

Recommendations:  Pressure for single storey buildings is 7 m for two storey buildings is 12 in of water for three storey buildings is 17m of water

The fire hydrant’s pressure should not be less than 1 Kg/sq. cm.

Minimum pipe size: 100 mm

Systems of Distribution:

1. Gravity System
2. Direct Pumping System
3. Combined System or Dual System.

Gravity System: Water is distributed by gravity only, to the consumers points. It is suitable for situations where the source of water is located at a sufficiently higher level than the town. This system is economical and reliable since no pumping is involved at any stage. It needs a lake or storage reservoir as a source of supply located at a sufficient higher level.

Direct Pumping System: Treated water is directly pumped into the distribution pipes by

means of high lift pumps without scoring anywhere.

• Pumps should be capable of being operated at variable speeds to meet the maximum and minimum demand and maintain sufficient residual pressures at various points of consumption. This system is not commonly preferred.
• Advantage is that during fire accidents, large quantities of water at high pressures can be pumped to put off the fire.

Combined or dual systems : “Pumping with storage system” or “Direct- indirect system”. In this system, the treated water is pumped at constant rate into an elevated reservoir as well as directly into distribution system.

, Thus it is a combination of gravity system and direct pumping system. This is most widely adopted system in water supply schemes for its obvious advantages such as Pumps can be operated with uniform speed at their rated capacities.

1. It is a reliable system as there is always some reserve water in elevated tanks to augment the supply during peak demands,
2. In case of lire accidents large quantities of water can be drawn
3. It is an economic and efficient system

Lay out of Distribution systems.:

• Dead end or tree system
• Grid iron system or Reticulation or interlaced system.
• Circle or Ring system
• Radial system

 Dead end system:

A supply main starting from the service reservoir is laid along the main road. The submains are connected to the main in both the  directions along the other roads. Submains divide into several branch lines. Service connections are taken form these branches to the individual houses.

Suitability: For old towns and cities with irregular and unplanned development

Advantages: Quite simple design ; Lesser number of cutoff valves; Easier expansions Short pipe lengths are required Cheap and economical 

Limitations: Considerable area gets affected during repairs.

• Water stagnation at dead ends leads to pollution
• Water rate of supply cannot be increased in case of fire breakouts.
• less successful in maintaining satisfactory pressures in the remote pans.

Grid iron system : Mains. submains and branches arc interconnected with each other. Main line runs through the centre of the area.

Suitability: Suitable for well planned cities.

Advantages:

• Since water reaches from different directions, sizes of pipes get reduced.
• Very small area gets affected in case of repairs.
• Due to free circulation, water cannot be polluted.
• More water can be diverted in case of fire breakout.

Disadvantages:

• More lengths of pipes and larger number of valves
• Costlier
• Design is difficult.

Ring system: Main pipe is laid peripherally.

• Laying of mains peripherally increase the pressure at farthest points.
• Suitable for towns and cities having well planned roads.
• Advantages and disadvantages arc same as Grid iron system.

Radial system: The area is divided into small distribution zones and in the center of each zone a distribution reservoir is provided Water from these reservoirs is supplied through radially laid distribution pipes running towards the periphery of the zone.

• Ensures high pressure and efficient water distribution.
• Suitable for cities with radial roads.

Design of Distribution System:

For head loss calculation, Hazen-Williams formula is more commonly used

Breakdown storage: It is the storage required to be provided in a distribution reservoir to take care of emergencies which may arise due to failure of pumps, failure of electric supply, etc. For this storage a lump sum provision of about 25 % of the total storage capacity of the distribution

reservoir is provided.

Fire storage : A provision of fire storage in a distribution reservoir is required to be made to provide water for fire fighting purposes.

• 1 to 4 lit/per/day for normal Indian conditions.
• Total capacity of D.R Balancing storage+ Break down Storage + Fire storage

APPURTENANCES IN DISTRIBUTION SYSTEM

1. Valves 
2. Manholes
3. Fire hydrants 
4. Water meters

Valves: Valves are provided in the pipelines to control the flow of water, to isolate and drain sections for test, inspection, cleaning and repairs to regulate pressures and to release or admit air.

• Sluice Valves or Gate Valves: used to regulate the flow of water through the pipelines.
• Butterfly valves : used to regulate stop the flow especially in large Size conduits.
• Globe Valve: To regulate flow.These valves are normally used in pipes of small diameter and as water taps.
• Check Valve: Also known as reflux valve or non return valve . A Check valve allows water to flow in one direction only and the flow in the reverse direction is automatically slopped by it. The reflux valve is invariably placed in a pumping main so that if the pump thus or slops, water is prevented from flowing hack to the pump and thus pumping equipment is saved from possible damage.
• Air Valve or Air-relief Valves: The air valve helps to admit air into the pipe when the pipe is being emptied or when negative or vacuum pressure is created in the pipe. Air valve operates automatically while allowing air to escape from or to enter a pipe. The air valves arc usually located at summits and also at changes in grade to sleeper slopes.
• Scour valve  or Blow-off Valves or Drain Valves: Provided for completely emptying or draining of the pipe for removing sand or silt deposited in the pipe and for inspection, repair, etc Located at dead ends and depressions or low points in the pipeline
• Pressure-relief Valves: Also called overflow towers arc provided to keep the pressure ¡n a pipeline below a predetermined value, and thus protect it against the possible Thus these valves are often placed at low points where the pressures are high. Further a pressure relief valve is usually provided on the upstream side of a sluice valve so that the pipe lying on the upstream side of the valve is relieved of water hammer pressure resulting from the sudden closure of the sluice valve.

Manholes: provided at suitable intervals along the pipeline for inspection and repairs. Usually spaced 300 to 600 m apart on large Pipelines.

Their most useful positions are at summits and downstream of main valves.

Fire hydrants: Hydrant is an outlet provided in a pipeline for tapping water many for the purpose of fire fighting. Also be used for withdrawing water for certain other purposes such a sprinkling on roads, flushing  streets, etc.

Generally fire hydrants are placed at all important road junctions and al intervals not exceeding about 300 m.

Water meters: Installed in pipelines to measure the quantity of water flowing through them.

Types: 

• Inferential type meters or velocity meters: Used for large pipes.
• Displacement type meters: Used for small pipes and domestic connections.

Location of leaks: For locating leaks in water supply pipes following methods may be used

• By direct observations
• By using sounding rods
• By plotting hydraulic grade line
• By using waste

— detecting meters(Deacon’s meter)

Sounding rods: A metal rod is inserted into the ground at the suspected portion. If there is a teak in the pipe the sound of the water escaping through the leak can be heard by placing the ear against the rod, or by means of an amplifying device such as aqua phone or sonoscope