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This would seem to indicate that the efficiency of the steam turbine increases with overload, at least up to a certain point.
In another test of a Curtis turbine, using dry saturated steam of 145 lbs. gauge pressure, the steam consumption at full load was 14.76 lbs. per E. H. P. hour, and at half load the rate was 15.95 lbs. per E. H. P. hour. The same machine using steam superheated 150° showed a steam consumption of 13.27 lbs. per E. H. P. hour, at full load.
A Curtis turbine carrying a commercial load on a 15hour run showed an average coal consumption as follows; the turbine was operated with one boiler independently of the other boilers in the battery, and the steam was not superheated: Coal consumed per E. H. P. hour, 1.86 lbs.
The highest type of modern reciprocating engine, · triple expansion, condensing, having steam jacketed cylinders, shows a coal consumption of 1.5 to 2 lbs. per H. P. per hour, assuming the evaporation to be 8 lbs. water per pound of coal.
THE HAMILTON-HOLZWARTH STEAM TURBINE
The Hamilton-Holzwarth steam turbine-Points of difference
between it and the Westinghouse-Parsons-Small clearances necessary-Stationary discs and guide vanes-Running wheels-Expansion of the steam and where it occurs-Action of the steam within the machine—Various stages in high and low pressure casings-Curvature of vanes—Purpose of stationary discs—Thrust ball bearings-Description of the gov. ernor and regulating mechanism-Close regulation-Method of changing speed while running. This turbine resembles the Westinghouse-Parsons turbine in some respects, prominent of which is that it is a full stroke turbine, that is, that the steam flows through it in one continuous belt or veil in screw line, the general direction being parallel with the shaft. But, unlike the Parsons type, the steam in the Hamilton-Holzwarth turbine is made to do its work only by impulse, and not by impulse and reaction combined. It might thus be termed an action turbine.
The Hamilton-Holzwarth steam turbine is based upon and has been developed from the designs of Prof. Rateau, and is being manufactured in this country by the Hooven-Owens-Rentschler Co. of Hamilton, Ohio. It is horizontal and placed upon a rigid bed plate of the box pattern. All steam, oil and water pipes are within and beneath this bed plate, as are also the steam inlet valve and the regulating and by-pass valves.
The smaller sizes of this turbine are built in a single casing or cylinder, but for units of 750 kilowatts and
larger the revolving element is divided into two parts, high and low pressure.
There are no balancing pistons in this machine, the axial thrust of the shaft being taken up by a thrust ball-bearing. The interior of the cylinder is divided into a series of stages by stationary discs which are set in grooves in the cylinder and are bored in the center to allow the shaft, or rather the hubs of the running wheels that are keyed to the shaft, to revolve in this bore.
The clearance allowed is as small as practical, as it is in this clearance between the revolving hub and the circumference of the bore of the stationary disc that the leakage losses occur. It should be noted that between each two stationary discs there is located a running wheel, and that the clearance between the running vanes and the stationary vanes is made as slight as is consistent with safe practice; otherwise leakage would occur here also, and besides this there would be a distortion of the steam jet and entrainment of the surrounding atmosphere, resulting in a rapid decline in economy if the clearance between the stationary and moving elements was not reduced to as small a fraction as possible.
As before stated, the stationary discs are firmly secured to the interior walls of the casing. At intervals on the outside periphery of these discs are located the stationary or guide vanes. These are made of drop forged steel. They are set in a groove on the outside edge of the disc and fastened with rivets. Both disc and vanes are then ground, giving the vanes the profile that they should have for the most efficient expansion of the steam. After this is done a steel ring is shrunk on the outside periphery of the vanes and the steam
channels in the disc. These discs are then placed in the grooves in the casing at regular intervals, and in the spaces between them are the running wheels.
The casing is divided into an upper and lower half. The running wheels are built with a cast steel hub having a steel disc riveted on to each side, thus forming a circumferential ring space into which the running vanes are riveted. A thin steel band or rim is tied on the outer edge of the vanes, thus forming an outer wall to the steam channels and confining the steam within the vanes. These vanes are also milled on both edges, on the influx and efflux side of the wheel, thus forming chem to the shape correspording to the theoretical diagram.
The running vanes conform in section somewhat to the Parsons type, but the action of the steam upon them and also within the stationary vanes is different. The expansion of the steam and consequent development of velocity takes place entirely within the stationary vanes, which also change the direction of flow of the steam and distribute it in the proper manner to the vanes of the running wheels, which, according to the claims of the makers, the steam enters and leaves at the same pressure, thus allowing the wheel to revolve in a uniform pressure.
Fig. 141 shows a general view of the HamiltonHolzwarth turbine, and the action of the steam within the machine may be described as follows: After leaving the steam separator that is located beneath the bed plate, the steam passes through the inlet or throttle valve, the stem of which extends up through the floor near the high pressure casing and is protected by a Hoor stand and equipped with a hand wheel, shown in Fig. 141. The steam now passes through the regulat
ing valve, which will be described later on. From this valve it is led through a curved pipe to the front head
of the high pressure casing or cylinder. In this head is a ring channel into which the steam enters, and from whence it flows through the first set of stationary vanes. In these vanes the first stageof expansion occurs, the velocity of the flow is accelerated, and the direction of flow is changed by the curve of the vanes in such manner that the steam impinges the vanes of the first running wheel at the proper angle and in a full cylindrical belt, imparting by impulse a portion of its energy to the wheel. Passing through the vanes of this wheel, the steam immediately enters the vanes of the second stationary disc, which are larger in area than those of the first, and here
occurs the second stage of expansion, another acceleration of velocity, and also the proper change in direction, and the steam leaves this distributer and impinges the vanes of the second