Invented by Lester Pelton, the Pelton wheel (sometimes known as the impulse water turbine) was an innovation that greatly increased the efficiency of water-driven industries. The buckets of the Pelton wheel have a divider running down the middle. This splits the flow of water striking them, slowing the water down and allowing the wheel to capture much more of its energy. Still used for hydroelectric power generators today, it first found employment in the mining industry that grew up around the California Gold Rush. A model of this fascinating mechanism can be constructed of materials available at any hardware store and is perfect for physics class projects and science fairs.
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Things you need
- 1 foot piece of 2-by-4 lumber
- 2 foot piece of 1-by-10 lumber
- Bar clamp
- Electric drill
- Wood screws
- Wood glue
- Exterior paint
- Luan sheet (1-by-1 foot)
- 8 shallow metal cans
- Plexiglas (about 1 foot square)
- Table saw
- 2-inch bolt
- 4 washers
Lay the 1-by-10 board on your work surface. Use wood glue to fix one of the ends of the 2-by-4 to it. The 2-by-4 should be attached in the middle of one of the long sides of the 1-by-10 board, pointing straight up. Use a bar clamp to hold the two pieces together until the glue dries.The 1-by-10 board will serve as the base of the model while the 2-by-4 will support the wheel itself.
Drill two holes through the bottom of the 1-by-10 board into the 2-by-4 support, and screw a wood screw into each hole to fix the two boards together more firmly than could be achieved with wood glue alone. The holes you drill should be equal in diameter to the centre shaft of the screw.
Drill a hole horizontally through the top of the 2-by-4 support, 2-inches below the top. The bolt that serves as the axle for the wheel will run through this, so make sure that the diameter of the hole is equal to the diameter of the bolt, and that the bolt fits snugly in the hole. Paint the completed frame (base and support together) with several coats of an exterior paint to protect it from water.
Drill a hole in the centre of the 1-by-1 foot piece of luan with the same diameter as a framing nail. Insert a framing nail into this hole, and tie the end of a piece of string to it. Tie the other end to a pencil so that the distance between the nail and pencil is 1 foot. Use this compass to draw a circle on the piece of luan. Cut the circle out with the jigsaw and then redrill the hole to the same diameter as the one in the 2-by-4.
Measure the inside dimensions of the metal cans. To make this a Pelton wheel, you will have to put a plexiglass divider into each bucket (can), dividing it vertically into two side-by-side compartments. Mark out eight such partitions on the surface of the plexiglass with a fine-tip marker or grease pencil, and cut them out with the table saw. Mix a batch of epoxy adhesive (being careful to follow the instructions on the back of the tube) and use it to fix the partitions in place inside the cans. Allow the epoxy to set before continuing.
Use the epoxy to glue the cans to the surface of the wheel, near the edge. If the cans have a large rim, you can build up a couple layers of epoxy so that it will sit flush. The cans should be spaced out evenly around the rim of the wheel. Wait for the epoxy to set, then paint the wheel with the same exterior paint you used on the base (don't paint the cans, as the paint will likely not adhere well to them).
Push the bolt through from the outer side of the hole in the 2-by-4 so that the end projects through the other side, over the base. Place two washers on it, then slide the wheel onto the bolt shaft such that the buckets are on the face of the wheel away from the support (so they don't get caught on it). Slide on another two washers, then place and tighten a nut on the end of the bolt so that the wheel doesn't wobble and so that it turns without too much resistance.
To operate your Pelton wheel, aim a jet of water (from a garden hose, for instance) at the buckets on one edge of the wheel. It will begin to spin faster and faster.
Tips and warnings
- The tins in which sardines and anchovies are sold make good buckets. Just make sure to wash them out thoroughly before using them, as any oil residue could interfere with the adhesion of the epoxy.
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