STEAM TURBINES

are modern engineering devices used for industrial Purposes, ship propulsion, and the production of electric power. They have displaced reciprocating engines in various directions. In general the steam turbine is distinguished from the older apparatus by its system of uniform rotary motion Place of reciprocating action and the application of various forms of impeller and guide vanes instead of Pistons and ports. In principle a turbine is a wheel or chamber in which the energy of a jet of steam (or water in hydraulic turbines) is applied to produce the rotation of a shaft. All steam turbines receive their steam at a higher pre ure, extract work from it by pa ing the steam through various arrangements of nozzles (or fixed blading) as well as moving blades, and reject the steam at a lower pre ure and consequently at a higher volume. If all, or nearly all, this drop in steam pre ure takes place in the stationary nozzles, the design is known as the impulse turbine. In mechanics, impulse is a force acting for a very short time, as in impact. On the other hand, when there is nearly an equal drop in pre ure in both the fixed and moving blades of a turbine as the steam is pa ing through them, the design is generally referred to as a _ reaction turbine. Reaction is utilized in various other prime movers besides a turbine wheel. Newton defined reaction as always equal and opposite to action, that is, the actions of two bodies on each other are always equal and in opposite directions. These names, impulse and reaction, have been adopted from the analogy of the water turbine, though, like a number of other terms current in engineering practice, they cannot be said to be a logical definition re what actually takes place in either e. Nearly all succe ful turbines work with the steam flowing axially, that is, parallel with the shaft spindle. The requirements of a number of industries for steam other than for power genera~ tion have resulted in the design of modified types of steam turbines, both impulse and _ reaction, which have generally come to be known by distinguishing names. Contrasted with the reciprocating engine, the steam turbine has more simplicity, needs le space and foundations, is free from cylinder-lubrication oil in the exhaust steam, has no unbalanced parts and vibration and sustains a uniform velocity in all degrees of a revolution as well as a good efficiency at light and over loads. It has become firmly established, and will be indispensable so long as steam machinery JS nece ary in industry, for it-is universally recognized as an enduring and economical type of heat engine. After the World War steam turbines developed to units with 60,000 kw. and 45,000 kw. (used by the large electric companies), but the general practice was to install units of 30,000 kw. capacity rather than larger machines. The le powerful units were favored because of greater flexibility in relation to the load at the station, and also because of economy of manufacture, due to the production of considerable numbers, which enabled their design, construction and operation to be standardized.