Anatomy of a hydro weir… It’s not a damn!

From the left. 1) Flow or level sensor on the left (the pole) the central screen harvests 50% of the remaining water. The cover on the left of the screen is removed in winter for an additional amount. On the right is the hands off flow. this notch is lower than the main screen

From the left. 1) Flow or level sensor  (the pole) the central screen harvests 50% of the remaining water after the ‘hands off flow’ amount . The cover on the left of the screen is removed in winter for an additional amount of water. On the right is the hands off flow. This notch is lower than the main screen . The penstock (pipe)  can be seen on the bottom left of the image

Whilst over at Tan y Coed on Friday I had a look at the lovely new weir for his farm hydro. Thought I’d have a go at explaining the function of a weir. There are quite a few  misconceptions around a weir or as its incorrectly called a ‘damn’.  The function of a weir as part of a hydro system is to ‘sort out’ the water. Its design decides how much to leave in the river (hands off flow) and how much of the rest of the water that can be harvested. The weir also decides the power output of the turbine (a level or flow sensor on the weir governs the spear valve (jet) on the hydro turbine in the valley below. The weir usually does not hold water back like a dam and its function is to get the water into the pipe. Behind the weir is usually filled with stones (gives less surface area for the water to push on the weir wall). The screen on this weir is made of stainless steel with drilled holes to allow a certain flow rate. The two screens built ta Hafod y Llan have a coanda screen fitted which is much more expensive but is self-cleaning under most circumstances (they don’t like pine needles though) But for Edward at this site it’s not really a hardship since he has a track passing the weir point and uses his high-tech cleaning device to keep the water flowing from the suspended peat in the water which wants to block the holes

cleaning-the-screen

This entry was posted in Hydro, Wales and tagged , , , , , , , , , , , , , . Bookmark the permalink.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s