Asian Phoenix Resources POWERPAL MHG-T2 - Manual (Page 16)

APPENDIX A – FOREBAY DESIGN
The instructions given on page 7 of this manual to design the forebay are adequate for
most cases. The most important aspects of forebay design are:
1) To allow a continual flow of water to the penstock so that the turbine keeps
functioning.
2) To have sufficient safeguards to prevent sand, vegetation and other debris
from entering the penstock which could cause blockages and disrupt the
turbine. This includes a safety aspect to keep away children and animals that
could possibly be injured by the suction of water entering the penstock.
3) To have an easy way to stop the water flow when changing the bearings etc.
The following diagram shows a simple forebay design that may be used to achieve all
the above goals.
the penstock. For example, if using the recommended 110mm diameter penstock then
95 x 1cm diameter holes should be drilled into the inlet screen (or 380 x 0.5cm
diameter holes etc.). The length of the inlet screen doesn’t matter, so long as the
minimum number of holes can be added. Bore casing with narrow, long slits is ideal.
Here, the forebay is made of a
waterproofed box situated
between the power canal (power
conduit) and the penstock. A
loosely fitting elbow is inserted
between the penstock inlet and
the main penstock pipe. Flow to
the penstock is cut off by pulling
the cord so that the inlet is out of
the water. The plugged drain is
used to periodically empty out
sand and leaves or else this can be
shoveled out. The perforated pipe
end further reduces litter intake.
Here the number of holes is
important so that flow is not
obstructed. To allow optimal,
uninterrupted flow, the open part
of the inlet screen should be at
least four times the open area of
The cover will help keep the forebay clean and may be locked to keep away children.
PowerPal™ T2 Turgo 16