the Carpentry Way: The Wooden Serpent                                                          

The Wooden Serpent

    
My wife and I were taking a drive up to Bennington Vermont the other day to check out the American Covered Bridge Museum. Bennington is a quaint town in the far Southwestern corner of Vermont. The museum was open but proved to be rather underwhelming. I did learn that at one point in time there were 600 covered bridges in Vermont, and around 100 remain.

On the way to the museum we drove up route 9, and approaching the dot on the map known as Searsburg I noticed something unusual by the side of the road, something snaking along and then ducking under the road only to emerge out the other side. This was something you certainly don't see every day: a wooden water pipe:


This pipe is part of a TransCanada Corporation's hydroelectric set up, and is in fact a penstock. It runs from TransCanada’s Searsburg Dam in Searsburg, VT to the Searsburg Station on the Deerfield River. The pipeline itself is about 3 miles long and is 8 feet in diameter on the inside. It’s made from wood staves (treated Douglas Fir - 3 million board feet were required!), similar in construction to a barrel; tongue and groove wood held together by metal bands. It flows water from the diversion (dam) to the powerhouse where the generator is housed.  The original pipeline was built in 1922 and last replaced in 1985.


It might need some attention again soon as it seems to leak fairly profusely from what I could see. These pictures don't show the leaking water on the underside of the pipe, but you can see some of the boards are wet on the outside:


This pipeline uses a wooden tension rod support cradle system. I've got to imagine that the leaking would cause problems in the wintertime with ice build up, and worse. I imagine that constant maintenance would be vital to realizing good long term service life. You have to keep the exterior clean and free from dirt to minimize opportunities for rot to begin. Repairs to wooden pipes are fairly straightforward though.

I thought this was a very neat thing to come across as I don't imagine there are many functional wooden penstocks left in North America:


Digging into it a little further, I learned that there are several functioning wooden penstocks in New England, including one just a bit further Northeast in Hillborough, NH. I'll have to check it out sometime.

I also found info on the company that had done the work to construct the penstock - Danbar, a Canadian outfit. A web page shows that there are still a few companies making wooden penstocks and that these wooden pipelines have certain advantages over other materials, in terms of handling corrosive materials, requiring minimal site preparation and they also handling abrasion very well. A fifty year durability is considered typical. Hooray for wood!

Here's a picture from Danbar's brochure showing some of the 1985 re-construction of the Searsburg penstock:



A couple more pages from that brochure:





I hope my fellow woodchucks found the above of interest. Thanks for dropping by the Carpentry Way.