CIVIL WORKS GUIDELINES FOR MICRO-HYDROPOWER IN NEPAL
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Figure 6.5 Transition from buried to exposed penstock, Jhankre
mini-hydro
Photo 6.11 Penstock, Purung
Photo 6.10 Site welding of penstock pipes, Jhankre mini-hydro
PVC pipes
PVC pipes with glued joints require provision for expansion,
at the same locations as for steel pipes.
Sizing of expansion joints
The sliding surface of the expansion joints should be machine
finished (such as in a lathe machine) to a tolerance of about
0.1 mm. The recommended thickness of the steel parts
(retainer and stay ring) is about twice the thickness of a well-
designed penstock pipe.
The gap in the expansion joint should be about twice the
calculated maximum pipe expansion length.
The maximum expansion length is calculated using the
following equation:
where:
= α (Thot - Tcold) L
L = pipe expansion length in m as shown in Figure 6.7. α =
coefficient of linear expansion in m/m °C of the pipe, which
depends on the pipe material. This coefficient relates to the
length that a material will expand per 1°C increase of
Figure 6.6 Sliding type of expansion joint