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to the shafting by which its propel- ler is revolved. Each set of propelling machinery develops 2500 shaft horsepower, or a total of 5000 shaft horsepower for the vessel, at full power. Under these conditions the turbines run at 2550 revolutions per minute with a reduction ratio to the propeller of 17.56 to 1 which gives about 202 revolutions per minute for the pro- peller. Each turbine consists of a rotor and an outer casing having an ex- ternal support at each end to carry the bearings in which the rotor re- volves. The rotor is fitted with rows of blades known as ‘‘moving’’ blades on to which the steam is directed by similar rows of blades known as ‘fixed’ blades projecting inward from the turbine casing or cylinder between the rows of ‘‘moving”’ blades. Steam issuing from the exit edge of one row of ‘‘moving’’ blades is guided by the “‘fixed’’ blades to the next row of “moving” blades and so on throughout the turbine. The lengths of the blades, both rotor and cylinder, gradually increase from the steam end to the exhaust and the openings between the blades are also correspondingly greater to allow for the passage of the steam, the volume of which gradually increases as the pressure falls during its passage through the turbines to the con- denser. The first stage of the high pres- sure ahead blading consists of an impulse wheel fitted with two rows of ‘“‘moving’’ blades and one row of “fixed”? blades. Following stages or expansions of the turbine are fitted with end-tightened reaction blading of Parsons’ type which allows large clearances in the radial direction. For running astern high and low pressure turbines are provided. The high pressure astern cylinder is in- corporated in the high pressure ahead turbine casing, but isolated from the same by a diaphragm gland consisting of a number of rows of rings arranged in the same man- ner as for the turbine glands. The low pressure astern cylinder is ar- ranged at the forward end of the low pressure ahead casing. When running astern, the valve supplying steam to the high pressure ahead eylinder is closed and the valve to the high pressure astern cylinder is open. Minimum Drag in Reverse The moving and fixed blades of the astern cylinders are oppositely handed to those of the ahead tur- bines in order to reverse the direc- tion of rotation. A vacuum is main- tained in both the high pressure and low pressure astern cylinders when the turbines are running in the ahead direction, and in the high pressure and low pressure ahead cylinder when the turbines are running astern. 14 Maximum economy of steam con- sumption is obtained by suitable ad- justment of the axial blade clear- ances. The low pressure ahead turbine is fitted with ordinary reaction blading throughout. The high pressure astern turbine is fitted with a single two-row impulse wheel only and the low pressure astern turbine has a two-row impulse wheel followed by three stages of reaction blading. Steam is led into one end of the high pressure turbines through which it flows with a continuous drop in pressure and thence to the low pres- sure ahead turbine from which it ex- hausts into a condenser fitted direct- ly to the under side of the low pres- sure casing. As the pressure of the steam, in its passage through the turbine, exerts an end pressure in the direction of its flow, a balancing ring termed a ‘‘dummy’”’ is fitted on the other side of the steam inlet. The function of this ‘‘dummy’”’ is to bal- ance the steam thrust by presenting an opposing surface of about equal diameter on which the steam can exert pressure, thus reducing the load to be earried by the thrust block fitted at the steam end of the turbine. This thrust block carries the unbalanced end thrust of the rotor, and maintains the rotor in its correct axial position, Flexible Coupling Used On the other end of the rotor there is provided a toothed claw and sleeve, which with a similar arrange- ment on the pinion shaft, constitute a flexible connection in the form of a double claw coupling between the rotor and the pinion shafts. Where the rotor ends project through the turbine casing steam sealed glands are fitted, These glands are made up of a series of fixed and moving rings alternated in the same manner as the turbine blades. Pockets, beyond these rings, which are maintained at a slightly above atmospheric pres- sure and segmental carbon rings be- yond these pockets prevent’ the escape of steam into the engine room, To guard against overspeed which might occur in the remote event of loss of propeller or breakage of shafting, an emergency governor is fitted at the steam end of each rotor to shut down the turbine by closing the steam valve before the speed can exceed a given figure. As a protection against failure in the supply of oil under pressure to the rotor bearings this emergency governor is also ar- ranged to shut off the steam supply to the turbine should the oil pres- sure fall below a certain value. The transmission of power to the shaft is by means of single reduction gears of the double helical type, cut on machines of special construction to obtain the high degree of accuracy necessary for quiet running. For MARINE REVIEW—September, 1934 lubricating the gear wheel teeth, jets are arranged spaced 11% inches apart across the whole width of the tooth face. Lubrication of the rotor and gearing bearings is by oil supplied. under pressure and the supply of oil to the gearing sprayers is taken from the same source, Special consideration has’ been given to the maneuvering of the main turbines. The control levers of both port and starboard sets have been brought to a single point and are so arranged that both turbines cau be controlled by one engineer. Auxiliary Machinery Particulars The auxiliary machinery is steam driven and operates under full boiler pressure, (250 pounds per square inch) saturated steam being supplied to all units with the exception of the generator sets which operate with the same degree of superheat (500 degrees Fahr.) as the main turbines. The main condensers are of the regenerative type and are designed to maintain a vacuum of 28% inches (barometer, 30 inches) in service. Two-stage feed heating is used, the first stage being supplied with the exhaust steam from the auxiliaries, and the second with steam bled from the main turbines. Special attention has been given to the feed water supply. A fresh water evaporator and filtrators are installed. An auxiliary condenser of vacuum type is installed provided with its own self contained circulating water pump and air pump. As mentioned before a_ pressure system of forced lubrication is used, the oil being supplied by two steam driven pumps, each of which is capable of dealing with the whole installation. Propeller shaft thrust blocks are of the Michell type. Yarrow Watertube Boilers Boilers, of which there are four in each vessel, are of the latest Yarrow -watertube type equipped with superheaters and _ airheaters. The tubes are all straight, giving rapid and unimpeded circulation and facilitating inspection and cleaning. A large proportion of the heating surfaces is exposed to direct radiant heat and the furnace is of such ¢ca- pacity that complete combustion is cbtained before the gases reach the tubes. The Yarrow superheater is con- structed of U-bend tubes expanded into a forged drum. The tubes are steeply inclined and _ self-draining and the large integral drum, which is hollow forged, conserves a valu- able reserve of steam for maneuver: ing. For access to both boiler and superheater tubes, it is only neces- sary to remove the manhole doors at the ends of the drums from which internal inspection and cleaning are (Continued on Page 40)