type, the function of the stationary blades is to give direction to the flow of steam.

Fig. 135 illustrates one stage of a 500 K. W. turbine in course of construction. It will be observed that there are three wheels, and that in the spaces between these wheels the stationary buckets or vanes are

placed, being firmly bolted to the casing. Fig. 136 shows sections of both revolving and stationary buckets ready to be placed in position. The illustration in Fig. 135 shows the lower or last stage. The clearance between the revolving and stationary blades is from to in., thus reducing the wastage of steam to a very low percentage. The diameters of the

wheels vary according to the size of the turbine, that of a 5,000 K. W. machine being 13 ft.

Fig. 137 shows a nozzle diaphragm with its various openings, and it will be noted that the nozzles are set at an angle to the plane of revolution of the wheel.

Fig. 138 is a diagram of the nozzles, moving blades and stationary blades of a two-stage Curtis steam turbine. The steam enters the nozzle openings at the top, controlled by the valves shown, the regulation of which will be explained later on. In the cut Fig. 138 two of the valves are open, and the course of the steam through the first stage is indicated by the arrows.

After passing successively through the different sets of moving blades and stationary blades in the first stage, the steam passes into the second steam chest. The flow of steam from this chamber to the second stage of buckets is also controlled by valves, but the function. of these valves is not in the line of speed regulation but for the purpose of limiting the pressure in the stage chambers, in a manner somewhat similar to the control of the receiver pressure in a two-cylinder or threecylinder compound reciprocating engine.

The valves controlling the admission of steam to the second and later stages differ from those in the first group in that they partake more of the nature of slide

valves and may be operated either by hand or automatically; in fact, they require but very little regulation,

DIAGRAM OF NOZZLES AND BUCKETS IN CURTIS STEAM TURBINE.

as the governing is always done by the live steam admission valves.

Action of the Steam in a Two-stage Machine. As previously stated, the steam first strikes the moving blades in the first stage of a two-stage machine at a

pressure of about 15 lbs. above atmospheric pressure, but with great velocity. From this wheel it passes to the set of stationary blades between it and the next lower wheel. These stationary blades change the direction of flow of the steam and cause it to impinge the buckets of the second wheel at the proper angle.

This cycle is repeated until the steam passes from the first stage into the receiving chamber or steam chest for the second stage. Its passage from this chamber into the second stage is controlled by valves, which, as before stated, are regulated either by hand or automatically. The course of the steam through the nozzles and blades of the second stage is clearly indicated by the arrows, and it will be noted that steam is passing through all the nozzles.

At this point it might be well to consider the question which no doubt arises in the mind of the student in his efforts to grasp the underlying principles in the action of the steam turbine. Why is it that the impingement of the steam, at so low a pressure, against the blades or buckets of the turbine, imparts such a large amount of energy to the shaft?

The answer is, because of velocity, and a good example of the manner in which velocity may be made to increase the capacity of an agent to do work is illustrated in the following way: Suppose that a man is standing within arm's length of a heavy plate glass window and that he holds in his hand an iron ball weighing 10 lbs. Suppose the man should place the ball against the glass and press the same there with all the energy he is capable of exerting. He would make very little, if any, impression upon the glass. But suppose that he should walk away from the window a distance of 20 ft. and then exert the same

amount of energy in throwing the ball against the glass, a different result would ensue. The velocity with which the ball would impinge the surface of the glass would no doubt ruin the window. Now, notwithstanding the fact that weight, energy and time involved were exactly the same in both instances, yet a much larger amount of work was performed in the latter case, owing to the added force imparted to the ball by the velocity with which it impinged against the glass.

Speed Regulation. The governing of speed is accomplished in the first set of nozzles, and the control of the admission valves here is effected by means of a centrifugal governor attached to the top end of the shaft. This governor, by a very slight movement, imparts motion to levers, which in turn work the valve mechanism. The admission of steam to the nozzles is controlled by piston valves, which are actuated by steam from small pilot valves which are in turn under the control of the governor. Fig. 139 shows the form of governor for a 5,000 K. W. turbine, and Fig. 140 shows the electrically operated admission valves for one set of nozzles.

Speed regulation is effected by varying the number of nozzles in flow, that is, for light loads fewer nozzles are open and a smaller volume of steam is admitted to the turbine wheel, but the steam that is admitted impinges the moving 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.

The Curtis Steam Turbine is the result of the investigations and experiments of Mr. C. G. Curtis of New