Water Supply Systems

Question 1

Trunk Main

Answer 1

The primary transmission pipe between treatment works and the service reservoir or between connected service reservoirs. Usually 450-600 mm diameter. Designed to carry 120% of average demand.

Question 2

Service reservoir

Answer 2

A tank which contains treated water and is situated on high ground, close to the area supplied. Balances inflow/outflow and provides contingency storage.

Question 3

Secondary Main

Answer 3

Generally larger diameter than inlet mains. Designed to carry 250% of average demand.

Question 4

Distribution mains

Answer 4

The mains in streets of diameter typically 80-250 diameter.

Question 5

Service connections

Answer 5

Connections between a distribution main and individual properties, generally 25 mm for domestic and 150 mm for industry.

Question 6

Phased implementation

Answer 6

Installation of the water supply system over a period of time to defer expenditure and ensure maintenance does not all need to happen at once.

Question 7

Pipes

Answer 7

Mostly metallic pipes (cast iron, spun iron and ductile iron pipes), however, new pipes are now polyethylene.

Question 8

Pipe jointing systems

Answer 8

Iron pipes need connections to new polyethylene pipes.

• Flanged Joint
• Tyton Flanged Joint

Question 9

Pipe installation methods

Answer 9

1. Conventional open trench
2. Trenchless techniques
3. Rehabilitation

Question 10

Valves

Answer 10

• Sluice value (stop/change direction of flow, mainly used to stop flow for maintenance)
• Pressure reducing valve (Line control valve maintains a present downstream pressure)
• Non-return valve (hinge gate prevents backflow)
• Double orifice air value (provides air purging capacity in pipelines with differing gradients)

Question 11

Tapping Ferrule

Answer 11

Draw off point at the crown of the main which incorporates a control valve

Question 12

Service reservoir: Minimum Storage

Answer 12

To even out hourly demand - 6 hours of 25% of average annual daily demand

Question 13

Service reservoir: Contingency Storage

Answer 13

To maintain supplied - 12 hours or 50% of average annual daily demand.

Question 14

Service reservoir: Total Capacity

Answer 14

18 hours supply or 75% of average annual daily demand

Question 15

Static systems pressures

Answer 15

Minimum system pressures 15-20 m in the main at peak demand. And maximum of 45-50 m is desirable.

Question 16

Surge Suppression Vessel

Answer 16

High grade epoxy coated steel containing instrumentation to monitor and maintain pressure and level inside the vessel. Also provides air cushioning against high pressures and pushes water into the main to prevent low pressures.

Question 17

Pressure Relief Valve

Answer 17

A diaphragm type valve hydraulically operated. If high surge pressure is experienced, actuated by line pressure through a pilot controlled system is will open rapidly but close gradually.

Question 18

Busting Disk

Answer 18

Usually installed as a safe guard against excessive CVH pumps to inhibit transducer fails. The disk bursts at a pre-set valve to relieve high pressure.