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The main consideration in any HDPE installation is the
management of thermal movement/expansion within the
system. There are 3 key methods of planning for thermal
movement in Geberit HDPE drainage systems.
These are:
• Controlled expansion
• Deflection leg
• Rigid fixing
Geberit HDPE Expansion Coefficient
Physical principal
All materials expand as temperature increases. If the
temperature falls, the material contracts.
5.2
Managing thermal
movement - Above
ground systems
0.17mm/m•K
Rule of thumb:
If temperature changes by
50°C, material will expand
or contract by 8.5mm/m
These expansion sockets must be anchored to control
the thrust forces that occur as the pipe pushes past the
seal ring, as well as to prevent uncontrolled movement
of the system that could result in potentially the pipe
‘pulling’ out of the seal ring joint.
Expansion socket - use of anchor brackets
Traditionally, plastic drainage systems have required that
pipe lengths over 4 metres are fitted with an expansion
socket which contains a lubricated seal ring for easy
movement of the pipe and an expansion gap within the
joint to allow for thermal expansion of the pipe work.
5.2.1
Controlled expansion
The main purpose of the anchor bracket is to prevent
any movement of the expansion socket. It is important
to fix each expansion socket with an anchor bracket.
If butt welded to other pipes/fittings, the anchor point
must be within 1.5 metres on the downstream side of the
expansion fitting allowing the anchor bracket to be located
near a strong, secure fixing point, i.e. the floor slab.
If this method is used horizontally on suspended pipework,
the drop rod must be of sufficient strength/ rigidity to
withstand the side ways thrust forces that occur when the
pipe pushes past the seal ring (see table below).
The thrust force
<<
P
>>
is the slide resistance between
the rubber seal and HDPE pipe. This force depends on
the pipe diameter.
Thrust force
<<
P
>>
when in operation
Ø
Thrust force P (kg)
40-63 10
75
12
90
20
110 30
125 40
160 70
200 100
250 150
315 220
Geberit Drainage Systems
System installation
