Installation manual

If the penstock simply discharges "full bore" (for example, to flush out sediment) then the

flow will be large, and there will be no pressure left. Pressure is all used up in pipe friction.

Normally the turbine uses jets to restrict the flow and convert the pressure into velocity to

drive the runner. The flow in the penstock will be controlled by the size(s) of jet(s) that you

use in your turbine(s). Larger jets will demand more flow, which will in turn create more

friction loss, and may reduce the pressure at the turbine. Smaller jets will minimise the flow

and the pressure will be slightly higher. Using a small bore jet may result in higher pressure

(due to lower flow rate) but using a smaller bore pipe will not, as it simply increases the

friction.

Another common myth is that pipe bends are the cause of a lot of penstock losses. In reality,

relative to the long hydro penstock, a few correctly sized bends will make no noticeable

difference as most friction loss is caused by the length of the penstock.

4.7.6. Laying and securing pipes

When laying the pipe try to do the following:

 Install a good strong intake structure.

 Secure the pipe against flash floods during the installation process.

 Obtain a good fall in the first 5-10 m of pipe.

 Lay the pipe on a gradual, always descending line where possible.

 Keep the number of high points to a minimum and vent these to avoid air locks,

pressure rises and pressure drops.

 Avoid siphon systems if possible.

 Once the pipe is in position, securely fasten the pipe line to rocks, trees, or ground

anchors to prevent it moving down the incline or being washed away in flood events.

4.7.7. Penstock valves

You may wish to install a valve below the intake, but this is rarely useful. If you do install a

valve at the top end of the penstock then the weight of water below will cause a vacuum that

may collapse your pipe or draw debris into it. It is good practice to fit a vent pipe just below

any such valve so the penstock can drain. This vent often helps air to escape while the

penstock is filling.

The turbine comes with valves that control the individual jets, but you may also wish to put a

larger valve on the penstock just prior to the manifold. Closing this valve allows you to work

on the manifold without draining the penstock. It also means that the penstock can be filled

and bled of air in advance of installing and commissioning the turbine itself. The air can take

time to find its way out via the intake and vents fitted.

You may need bleed valves at high points if the penstock slope is not continuous. These are

only used to remove air and can be closed during operation.

Finally you may wish to install a flush valve at the bottom end of the penstock so that you

can flush out sediment.

None of these valves are always essential - each has possible merits.