222 THE PROPELLING MACHINERY OF THE U. S. S. LEVIATHAN. 



arranged between the two casings, so that the astern casing expands forward and 

 the mid-pressure casing aft. 



The rotor has an impulse wheel with four rows of buckets about ii feet 6 

 inches mean diameter at the steam inlet end, and this is followed by ten expansion 

 stages of impulse-reaction blades on a drum construction, having a diameter of ap- 

 proximately lo feet lo inches. There are sixty rows of impulse-reaction blades in 

 casing and rotor, the blade heights varying from 5^'2 inches to 13^ inches. 



A radial fin type of dummy is fitted to the steam belt, and the overall length 

 of the rotor drum is about 17 feet (Fig. 5, Plate 97). 



The rotor adjustment block is arranged in the pedestal between the two casings. 



When the mid-pressure ahead turbine is operating in triple series — that is, re- 

 ceiving exhaust steam from the high-pressure ahead — the impulse wheel is by-passed 

 and the work done by the steam is entirely through the impulse-reaction drum blad- 

 ing. It is only when this turbine is being operated under "maneuvering" conditions 

 that the impulse wheel buckets are in use, in which case the steam from the regulator 

 valve passes into three sets of nozzles arranged in the top half casing. Two ex- 

 haust branches, each 48 inches diameter, pass the steam over to the low-pressure 

 ahead turbines of the outboard shafts. 



Low-Pressure Ahead {Port and Starboard Outboard Shafts) . — These casings 

 are exceptionally large, made of cast iron and built up in a number of sections, and 

 the two halves are bolted together at flanges on the horizontal center line. 



The design of these turbines has this unusual feature — the dummy is arranged at 

 the aft end in the main exhaust belt, consequently the interior of the rotor is always 

 full of steam at the pressure of the inlet belt, and this is done possibty to overcome 

 any tendency of the rotor to distortion under varying conditions of temperature. 



The dummy is of the regular radial fin type. 



Cast-iron pedestals are bolted on to facings at each end of the casing body and 

 support the rotor bearings, etc. 



The diameter of the rotor drum is 12 feet 9^ inches, and it is made up of three 

 forged steel drums bolted together at internal flanges. The end discs are also bolted 

 to the drum with bolts. 



The overall length of the rotor drum and dummy is approximately 21 feet 3 

 inches (Fig. 6, Plate 98). 



There are sixty-three rows of impulse-reaction blades in casing and rotor, ar- 

 ranged in twelve expansion stages, the blade heights varying from 5J4 up to 24 

 inches. 



The internal diameter of the casing at the exhaust barrel is 16 feet gYz inches. 



The exhaust nozzle opening has an area of 81^ square feet, and directly under 

 this are arranged the fixed feet which transmit the propeller thrust to the hull, the 

 steam inlet branch to each casing being 48 inches diameter. 



Lozv-Pressure Astern {Port and Starboard Outboard Shafts) .■ — -These casings 

 are bolted rigidly to the aft end of the low-pressure ahead. The body is made of 

 cast iron built up in four sections, a vertical joint being arranged about the middle 



