. Electric traction and transmission engineering . 284 TRACTION AND TRANSMISSION. through one or more nozzles at a velocity equal to V2 gHfeet per second, where g is the acceleration due to gravity= 32 ft. per sec. per sec, and H is the head or height ofwater in feet. Each bucket forms two cups divided by acentral ridge which separates the impinging water into twoparts, each part being deflected backward to one side of the. Fig. 118. wheel by the bucket. The effective head is that from thelevel of headwater to the nozzle, the head from the latterto the tailwater being lost; consequently the im
. Electric traction and transmission engineering . 284 TRACTION AND TRANSMISSION. through one or more nozzles at a velocity equal to V2 gHfeet per second, where g is the acceleration due to gravity= 32 ft. per sec. per sec, and H is the head or height ofwater in feet. Each bucket forms two cups divided by acentral ridge which separates the impinging water into twoparts, each part being deflected backward to one side of the. Fig. 118. wheel by the bucket. The effective head is that from thelevel of headwater to the nozzle, the head from the latterto the tailwater being lost; consequently the impulse wheelshould be placed as low as possible. The flow of water isregulated by needle valves or by deflecting the 118 shows a twin Pelton water wheel with its hy-draulic relay governor. Governors are used on both types of water turbines forautomatically effecting the opening and closing of the regu- HYDRAULIC STATIONS. 285 lating gates or for deflecting the jet from the buckets of im-pulse wheels. As the force required for this purpose is verylarge, it is evident that the centrifugal ball governor cannotdirectly control the gate opening, but must do so throughthe intervention of a relay. Two general types of relay areused: mechanical relays, which derive power for their opera-tion from the water wheel by means of gears, pulleys, orother mechanical devices, and hydraulic relays, which areoperated either
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