ing blades with the same velocity always, no matter whether the volume be large or small. With a full load and all the nozzle sections in flow, the steam passes to the wheel in a broad belt and steady flow.

FIG. 198. 5,000 KILOWATT GENERATING UNITS.

Comparison of space occupied and size of foundations. Modern Engine Type Unit and a Westinghouse-Parsons Turbine Type Unit of similar rating and overload capacity.

Ques. 735.-What great advantage does the steamturbine as a prime mover for an electric generator possess over the reciprocating engine?

Ans-The advantage of a high speed of revolution,

whereby there can be a great reduction in the size, weight, and cost of the direct-driven generator.

Ques. 736.-Give approximately the over-all dimensions of a Westinghouse-Parsons turbo-generator unit of 5,500-kilowatt, 11,000 volt capacity, of the revolving field type, speed 750 revolutions per minute, vacuum to be 271⁄2 inches.

Ans.-Length 47 feet, width 13 feet, and height 14 feet to top of gallery-ring.

Ques. 737.-What amount of floor-space would a reciprocating engine and direct-connected generator of equal capacity with the above occupy?

Ans.-The generator would be 42 feet in extreme diameter, its weight would be 445 tons (speed to be 75 revolutions per minute) and it, together with the fourcylinder piston engine, would fill a space 40 feet wide by 60 feet long, and tower 45 feet in height.

Ques. 738.-Describe in general terms the construc

tion and principles of operation of the WestinghouseParsons steam-turbine.

Ans.-The Westinghouse-Parsons steam-turbine is fundamentally based upon the invention of Mr. Charles A. Parsons, who, while experimenting with a reaction turbine constructed along the s of Hero's engine, conceived the idea of combining the two principles, reaction

FIG. 200. Shows a 600 H. P. machine with the upper half of the cylinder, or stator as it is termed, thrown back for inspection.

and impulse, and also of causing the steam to flow in a general direction parallel with the shaft of the turbine. This principle of parallel flow is common to all four types of turbines, but is perhaps more prominent in the Westinghouse-Parsons and less so in the De Laval. The cylinder, or stator, as it is termed, is divided longitudinally into an upper and a lower half flanged and bolted together. There are three sections or drums, gradually increasing

in diameter from the inlet to the third and last group of blades. This arrangement may be likened in some measure to the triple-compound reciprocating engine.

Ques. 739.-Describe the arrangement of the blades or buckets in the Westinghouse-Parsons steam-turbine. Ans.-There are two kinds of blades, viz., stationary blades and moving blades, but they are similar in shape, being of the same curvature. These blades are made of hard drawn material, and are set into their places and secured by a caulking process. The stationary blades project from the inside surface of the cylinder, while similar rows of moving blades project from the surface of the rotor, or revolving drum. When the upper half of the cylinder is in position each row of stationary blades fits in between two corresponding rows of moving blades. Ques. 740.—Are these blades all of the same length?

Ans. They are not.

for the shortest to

The length varies from 1⁄2 inch inches for the longest, according to

their location. The shortest blades are placed at the steam end of each section and the longest blades are placed at the opposite end.

Ques. 741.-What is the clearance between the blades as they stand in the rows?

Ans. The clearance between the blades as they stand in the rows is 8 inch for the smallest size blades and 1⁄2 inch for the larger ones, gradually increasing from the inlet to the exhaust. In the 5,000 kilowatt machine the clearance at the exhaust end between the rows of blades is 1 inch.

Ques. 742.-What is the general direction taken by

the steam in its passage through the Westinghouse-Parsons turbine?

Ans. The steam entering at the smaller end of the cylinder presses first against the shortest blades and then passes on through in the form of spiral or screw line about the rotor, continually pressing against new and gradually lengthening blades, thus doing work by reason of its velocity.

MOVING BLADES

FIG. 201. SECTIONAL VIEW OF FOUR ROWS OF BLADES, OF A WESTINGHOUSEPARSONS TURBINE.

Ques. 743.-As steam presses equally in all directions, is there not a very heavy end-thrust exerted by the rotor?

Ans.-There is not. The pressure in either direction is perfectly balanced by means of balancing pistons placed on the steam end of the rotor. The diameters of these pistons correspond to the diameters of the different drums or sections.*

Ques. 744.-About what is the velocity of the steam in the Parsons turbine?

*The theory and action of these balancing pistons is fully and completely described in Swingle's "Twentieth Century Hand Bock for Engineers and Electricians."