Caddo Creek Dam – Pt II

How about HP?
Looking at a chart in the book of capacities of Hunt-Francis turbines with the 7,560 cu.ft. water a minute we find that we could get 74.41-hp with a 36-in wheel and 12-ft head – requiring 3,992 cu.ft. min ..

but .. the casing that the turbine sits in is approximately three times the dia of the turbine wheel (or .. maybe not. See the bit later on the exterior mounted turbine). For a 36-in wheel that means a casing 9-ft in dia. .. and that for a horizontal mounted turbine .. it would be 4-1/2 feet from the shaft to the floor. That would mean that instead of 12-ft of head we would have 12-4.5 or 7.5 ft. of head. That would reduce our hp to around 37-hp.

What if we used a 24-in wheel? That would require a 6-ft dia casing or 3-ft from shaft to floor and leave us with a 9-ft head – and give us 22.24-hp.

Thing is .. the pump-house is already made. I have about 8-ft height in the lower section to put the turbine wheel and generator etc. inside. That would seem to restrict me to the smaller wheel and 22+ hp.

Turbine Location
The turbine wheel/casing doesn’t HAVE to go inside the power house. Check this out. Here, all of that is mounted outside with a shaft that pierces the wall to the generator. The Penstock (sluice/pipe) that comes out of the building is the feed (it is under the floor). There is a sluice-gate inside the building to control the turbine. The near pipe returns the water to the river/stream.

This would be cool simply because of the added ‘stuff’ for the scene. The up-side is that you could use a larger dia wheel/casing since the bulk is outside the building.

I just think this is neat!

I did some proportional calculations from the photo. The casing dia and length is about 1.6 x the dia of the smaller discharge pipe on the end of the casing. That elbow is perhaps 1/2-inch thick (or so) .. so .. I’m going to make a WAG and bump those numbers up to 1.7-1.8 x the ID of the pipe. The reason for that is that from the book you can get the needed pipe dimensions for whatever combination of wheel dia and head .. from which you get Cu.Ft. Per min .. and roundy-round back to the pipe. I’m seriously thinking of this since in ‘my world’ the 1st floor of my pumphouse was retrofitted by installing a generator. Putting the turbine on the exterior works for two reasons ..

  1. It would just LOOK COOL .. more ‘stuff’ to look at ..
  2. originally the pumphouse has that 1st level containing just the sluice-gate and assorted filtering stuff (like the trash rack). A small generator wouldn’t take up much room. A generator is basically an electric-motor that is driven externally and electricity taken off of the leads. I figure if I am generating 35-hp from the turbine then the generator should be approximately the same size as a 35-hp electric motor (about 10-in dia and 15-in long let’s say).
Scratching
Once I had the dam created in Sketchup I could print off the various bits and glue them to some .040″ Styrene using one of those glue sticks. Nice thing about that is warm water dissolves the glue leaving you with your own personal ‘kit’.
I couldn’t find my model putty so I grabbed some automotive spot putty. Works just as well far as I have ever noticed.

Still have to add the radius at the bottom.

New Rock
I mentioned that I was running into problems I hadn’t thought through (meaning I hadn’t considered them). Since the turbine shaft height off the water depends on the dia of the turbine/casing .. that has to be taken into account when figuring the head. That simply means the height that the dammed water falls from the dam to the turbine. It came to me that .. hey .. the dam didn’t have to rest at the level of the creek. In “my world” there had been a small falls at the point the dam was built which raises it up! A couple pieces of blue Styrofoam and the dam now sits 1-1/2″ higher. In O Scale that means six feet of added head. Cool.

The face of the dam is basically finished as I added the radius at the bottom.



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