DAM VALVE-THE ELECTRICITY FACTOR

THE ELECTRICITY FACTOR

So how does the water in a dammed up lake generate electricity? The answer lies in the potential energy that the deep and heavy volume of water creates. When piped through a tube into a generator turbine, this great weight or mass of water will act to move the turbine blades, which causes them to rotate rapidly. A common shaft to a generator connects to the rotating turbine blades and creates the electricity.

In modern hydroelectric dams, the water input lines or penstocks to these turbines are often very large, sometimes up to 15 feet or more in diameter. The larger volume of water in feet per second means that a larger generator can be rotated, and thus more electricity can be generated.

These small-diameter utility lines and valves are located in a large dam installation.Each tunnel providing water to a ­turbine must be unique to produce the greatest amount of water energy. Since the turbines are complex mechanical devices, they occasionally require maintenance. To repair them, the water ­supply must be stopped during the repair period, which can last for months. Because of this, each turbine tunnel or pipe must have its own block valve to allow repairs to be made. The turbine block valve in use in many dams today is the butterfly valve, because of its small footprint when compared with gate valves or ball valves.

These butterfly valves can be massive, and in many cases, they are built into the body of the dam. Therefore, complete replacement is cost prohibitive. This means they have to be designed so that they can be repaired in place.

One of the oldest and probably still the largest butterfly valve installation in the United States is in Exelon’s Conowingo Dam in Pennsylvania. The huge, 27-foot, port-size butterfly valves are big enough for a two-lane highway to pass through them. These valves have been operating since the dam opened in 1927 and are still in use today, providing a means of dewatering the turbines if repairs or upgrades are needed.

Although not huge by Conowingo standards, the butterfly valves in Hoover Dam are also impressive. They were designed and patented by the ­United States Bureau of Reclamation (USBR) in 1934. There are 16 156-inch butterfly valves, each one ­isolating a power-generating turbine.

To provide an idea of their size, each requires a 12-inch bypass line. These unique monsters are built into the dam so their removal in case of repair would be almost impossible. Their existence has created opportunity for the ultimate valve repair field service.

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