Water

Designing homes to use water efficiently, reduce costs and cope with more frequent droughts or storms.

Pipes, valves and controls

Find out about:

  • hot water pipe requirements
  • pressure rating of thermoplastic pipes
  • de-rating (rate of loss of strength) factors of some commonly used pipe materials
  • valves and controls for storage water heaters
  • valve requirements.

Hot water pipe requirements

Hot water pipes must be able to withstand the maximum temperature of the water being piped. Pipe material may be copper or an appropriate thermoplastic material.
Materials suitable for hot water supply pipes include:

  • copper
  • polybutylene (PB)
  • chlorinated polyvinylchloride (CPVC or PVCc)
  • random polypropylene (PP-R)
  • cross-linked polyethylene (PEX).

Thermoplastic piping should not be used where a hot water system includes an uncontrolled heat source such as a wet back or a solar heating system.

G12/AS1 and AS/NZS 3500.4 require the first metre of length of pipe from water heaters to be in copper.

Grades of PEX vary, and few grades will tolerate 100°C water for any significant length of time.

Pressure rating of thermoplastic pipes

Pipes are classified according to their pressure rating (PN) at 20°C. For example, a pipe rated PN16 is rated for a pressure of 160 MPa at 20°C. Thermoplastic pipes lose strength and ability to withstand the pressure with increasing temperature, and this differs with different materials.

De-rating (rate of loss of strength) factors of some commonly used pipe materials

Temp
(°C)		 Polybut-
ylene		 Polyvinyl-
chloride		 Chlorin-
ated polyvinyl-
chloride		 Polyeth-
ylene		 Cross-
linked polyeth-
ylene
           
20 1.0 1.0 1.0 1.0 1.0
27 1.0 0.9 1.0 0.9 0.7
38 0.9 0.6 0.8 0.8 0.8
49 0.8 0.4 0.7 0.7 0.8
60 0.7 0.2 0.5 0.4 0.7
71 0.6 * 0.4 * 0.7
82 0.6   0.4   0.6
93 0.4   0.2   0.5
104 *   *   *

* Not resistant to long-term service beyond this temperature.

Valves and controls for storage water heaters

While low pressure water supply systems require few valves, they are required with mains pressure and more complex systems.

Brands and pressure ratings of valves must be specified for particular systems.

Valves are frequently supplied in matched sets to avoid cross mixing and ensure the correct hierarchy of pressure settings.

Non-mandatory valves should also be considered for ease of maintenance and system control.

Valves must be installed so they are:

  • accessible for repairs and maintenance
  • protected from damage
  • protected from frost.

Unqualified people should not alter, remove or dismantle valves on any potable water supply system.

Valve requirements

Valves and control device Function Required Recommendend
Isolating valve Manually operated valve to isolate one section of the system. At the property boundary for all mains connected installations adjacent to tank outlet where there is on-site supply. • At the entry point to the building.
• At a supply tank.
• At the hot water cylinder.
• Any other fixture where frequent maintenance is required.
Pressure limiting valve Limits the pressure within pre-set range. With mains pressure systems where the water pressure could exceed the pressure rating of the pipe material or hot water cylinder. • Where mains pressure is very high or fluctuates excessively.
Non-return valve Prevents reverse flow within or from the system. At the hot water cylinder to prevent water from the cylinder from returning to the water main or being delivered from cold water outlets if mains supply fails. • At the property boundary.
• At any pump.
Line strainer Filters particles of solid matter from the water to protect other valves further downstream. Where other valves could be damaged by solid materials. • At the entry point to the building.
• At the hot water cylinder on all systems.
Pressure reducing valve Reduces the pressure to a pre-set level. To reduce mains pressure on a low pressure hot water system. • To provide balanced low pressure cold water to other fixtures on the same system.
Expansion control valve (cold water) Releases pressure in the cold water feed pipe caused by the expansion of water in the storage water heater cylinder during normal operation. On any valve-vented hot water cylinder. • Retrofitted to all existing valve-vented hot water cylinders (low and mains pressure).
Pressure relief valve (PRV) Releases pressure in the storage cylinder if it rises above the pre-set limit. On low pressure (<120 kPa) valve-vented hot water systems that do not incorporate an open vent pipe.  
Temperature/pressure relief valve (TPR) Operates above a pre-set temperature and pressure. On valve-vented hot water systems >120 kPa. • All valve-vented systems (low and mains pressure).
Temperature limiting thermostat Controls the temperature of the water. On the hot water delivery to all personal hygiene fixtures and on wetback installations. • On all hot water delivery to personal hygiene fixtures.

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