Find out about:

• flow rate
• pipe sizing
• water pressure
• pipe design
• regulating flow and pressure
• installation
• noise and air locks in pipework.

Flow rate

Flow rate is affected by the:

• available water pressure
• pipe diameter
• the length and the number of bends of the pipe.

Every sanitary fixture must be connected to the water supply by a pipe that provides an adequate flow rate not less than that shown in the following table (adapted from G12/AS1: Table 3).

Fixture	Flow rate (l/s)/	Flow rate (l/min)
WC cistern	0.10	6
Bath	0.30	18
Basin	0.10	6
Shower	0.10	6
Sink: standard tap	0.12	7
Sink: aerated tap	0.10	6
Laundry tub	0.12	7
Dishwasher	0.20	12
Washing machine	0.20	12

Pipe sizing

Pipes must be sized to achieve the flow rates in accordance with G12/AS1: Table 3 or the pipes sizes in accordance with G12/AS1: Table 4.

When calculating pipe size, the speed of the water (velocity) moving through the pipes must not exceed 3.0 m/s.

Manufacturers’ recommendations must be referred to for pressure and flow information when selecting tempering valves and outlets (taps, mixers and shower heads).

Water pressure

If water pressure is not sufficient (i.e. less than 50 kPa or 5 m head):

• provide a water storage supply tank to give adequate head
• fit a pressurising pump to supply tank

If water pressure is too high (i.e. greater than 500 kPa or 50 m head):

• install a pressure reducing valve
• provide a water storage supply tank to control the head.

Pipe design

Factors affecting pipe design include the following:

• Internal diameter (ID) of the pipe – Pipes are generally referred to by their inside nominal diameter (DN), but a pipe rated as DN 15 may have an actual inside diameter ranging between 10–18 mm. An effective reduction in the internal diameter of a pipe will result in a drop in the pressure and flow rate.
• Number of bends and fittings a pipe run serves – The more bends in a length of pipework or number of fittings served by a length of pipework, the lower the flow rate for the particular pipe diameter.
• The temperature of the water – Temperature, particularly in plastic pipes, also affects flow rate of water. As the temperature increases, the maximum working pressure of the pipeline decreases and the service life of the pipe will decrease. Some plastic systems are available in a number of pressure classes – the same material may have a slightly different composition and wall thickness providing a range of temperature/pressure options.

Regulating flow and pressure

• A flow regulator maintains a constant flow independent of supply pressure. For example, if someone is in the shower and the kitchen tap is turned on full, the temperature and flow are likely to remain more stable if the flow is controlled. Limiting the flow for a tap or appliance to a reasonable rate helps balance the available pressure throughout the system. Regulating flow allows a simpler design and minimum pipe sizes as peak flow rates can be specified accurately and can also reduce noise, splashing taps, and water hammer.
• A pressure regulator maintains a constant pressure, independent of flow. It is typically used to limit pressure in mains-supplied hot water systems or where high pressure may lead to problems such as burst pipes or leaking float-operated valves, within the system.

More information

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