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DD-43 Casin - Machinery

The main propulsive machinery comprises an installation of Parsons turbines in combination with a small reciprocating engine, for use at cruising speeds up to 15^ to 1.6 knots. The turbines are designed to run at 550 r.p.m. when developing 16,000 S.H.P., and the cruising engine is designed to develop 700 I.H.P. at 270 r.p.m., corresponding to the speeds noted in preceding paragraph.

The engines are arranged on two lines of shafting which provides one ahead and one astern turbine on each shaft, the L.P. turbine including an astern turbine in the after end of its casing. The cruising engine is on the port shaft forward of the L.P. turbine, and fitted with clutch coupling for disconnecting from the turbine shaft when not in use. In addition to the cruising engine, two cruising stages are provided in the M.H.P. turbine casing, which are bypassed at the higher speeds alone or in combination with the cruising engine.

  • Full Speed Ahead. - The two ahead turbines are used for this purpose, steam being admitted to the M.H.P. turbine, bypassing cruising stages, and expanded through the L.P. turbine into the condenser. Under this condition the astern turbines revolve idly in a vacuum, which is maintained through the exhaust connections to the condenser.
  • High Cruising Speeds. - Two turbines are used at these speeds, steam being admitted to the M.H.P. turbine cruising stages, thence through the M.H.P. turbine and L.P. turbines, exhausting into the condenser ; the astern turbines revolving idly in a vacuum.
  • Low Cruising Speeds. - The M.H.P. and L.P. turbines are used for these speeds in combination with the reciprocating engine, steam being admitted to the latter, which exhausts through the reheater into the M.H.P. turbine, expanding through cruising and main stages into the L.P. turbine, and exhausting into the condenser ; the astern turbine revolving idly in a vacuum.

The reheater is installed in the cruising-engine exhaust to the M.H.P. turbine to assure a dry steam supply to the latter and consequent improved economy of operation. It contains 112.91 square feet of heating surface, the heating agent being exhaust steam from the cruising-engine cylinder jackets. For astern motion at any speed the astern turbines alone are used. The cruising engine does not reverse. The engines are controlled from the working platform.

When maneuvering, independent operation of the port and starboard shafts is accomplished by closing the valve, in the M.H.P. turbine exhaust trunk to the L.P. turbine, and opening the exhaust valve, permitting the M.H.P. turbine to exhaust direct to the main condenser via the exhaust trunk. The valve is of the self-closing type, closing toward the M.H.P. turbine, in order to prevent a back flow of steam to the latter, should the port ahead maneuvering steam be suddenly turned into the L.P. turbine. This valve is also arranged to be locked shut, thus securing positive isolation of the port and starboard turbines from each other. Each shaft can then be operated independently, either ahead or astern, as follows: The port shaft is controlled by the maneuvering valve, which admits steam to either the L.P. or astern turbines as desired. The starboard shaft is correspondingly controlled by the main throttle valve for ahead motion, and the maneuvering valve for astern motion, the steam exhausting direct to the condenser in either case, via the exhaust trunks, respectively. The cruising engine, though not used, is not necessarily disconnected when maneuvering. It is designed to be dragged at about 400 r.p.m. without injury.

Each turbine is of the customary Parsons design, consisting of a fixed part or cylinder, and a moving part or rotor, fitted with guide and moving blades respectively. The cylinders are of hard close-grained cast iron, divided into two parts at the axis on a horizontal plane, the lower half being provided with feet for bolting to the seating. Each rotor is built up of a drum of forged steel, securely fastened to a forged-steel wheel at each end, that is forged in one piece with the rotor shaft. The rotors are perfectly balanced when entirely completed, in order to prevent vibration when running. The dummies and rotor-shaft glands are steam packed with the usual labyrinth packing.

A micrometer for measuring the dummy clearances is provided at the forward end of the M.H.P. turbine only. All other turbines being fitted with dummy strips of the circumferential clearance type and having greater longitudinal blade clearances, do not require micrometer adjustment ; a finger plate pointing to three scribed marks on the shaft, indicating the mean and extreme safe fore and aft positions of the moving parts, alone being necessary for the other turbines.

There is a main bearing at each end of each turbine for supporting the rotor. All bearings consist of a pedestal cast with the turbine casing and fitted with bottom brass and cap.

The M.H.P. turbine and L.P. and astern turbine are provided with thrust blocks at the forward end, consisting of a number of brass rings, in halves, fitted into corresponding collars on the shaft. The lower half of the M.H.P. turbine thrust bearing is for taking the ahead and the upper half the astern thrust, and that on the L.P. and astern turbine takes both ahead and astern thrust on the entire surface of the thrust collars. All main bearings and thrust bearings are fitted with a closed system of forced lubrication, as described elsewhere.

A hand turning gear is provided for each line of shafting. It comprises a worm wheel on each shaft, meshing with a worm operated by a ratchet wrench, the worm being readily thrown in and out of gear. An efficient lifting gear is provided for the main turbines. The lifting mechanism is hand operated.

There are two lines of shafting, of four sections each, consisting of two line shafts supported by three spring bearings, one stern-tube shaft supported by the two stern-tube bearings, and one propeller shaft supported by the strut bearing. All stern-tube and strut bearings are lined with lignum vitae and the shafts are composition bushed at these bearings. The shafting within the stern tube is covered with a casing of seamless drawn brass tubing, shrunk on.

There are two three-bladed propellers. The port propeller is left-hand and the starboard propeller is right-hand. The blades and hubs are of manganese bronze and cast in one piece. The blades are true-screw machined to pitch.

There is one main condenser of circular section located on the center line of the vessel between the turbines. It is of the curved-tube type, with the tubes expanded in both tube sheets, which are bumped outward to a radius of ninety-five inches. Two Warren, vertical, twin, bucket, single-acting air pumps are provided for the main condenser. Each pump has a single steam cylinder 14 inches in diameter, and two water cylinders 28 inches in diameter each, with a common stroke of 18 inches. The condenser is provided with a small centrifugal circulating pump, driven by an independent single reciprocating engine, for use in port and when maneuvering. Under normal service conditions the circulating water is forced through the condenser by means of a scoop on the main injection, the circulating pump not being used. The customary Parsons vacuum augmenting apparatus is provided, consisting of a small condenser of the curved-tube type, steam jet and water seal, connected to the main air-pump suction piping in the usual manner.

A feed and filter tank of about 800 gallons gross capacity located in the port forward end of the engine room. The filter chamber is in the top of the tank, and so arranged that the entering water will flow over the top of a plate and leave through perforated plates in the bottom of the chamber after passing through the filtering material.

There is an auxiliary condenser in the auxiliary-machinery room connected through the auxiliary exhaust line to all auxiliary machinery. It is of the curved-tube type with tubes rolledin both tube sheets. The condenser has a 6-inch X 8-inch X 8-inch X 7-inch Warren, horizontal, single, double-acting, combined air and circulating pump. Two Warren 15-inch X 10-inch X 16-inch main feed pumps of the vertical, double-acting, single type are located in the port forward corner of the engine room. The pumps have suctions from the main feed tanks and discharge to the boilers through the feed-water heater or by passes. There is a feed-water heater of the direct-flow type installed in the engine room, on the discharge side of both the main and auxiliary feed pumps. The heating agent is the exhaust steam, a back pressure being kept in the auxiliary exhaust line for this purpose by means of a spring relief valve at each condenser connection, opening toward the condenser.

The main bearings, thrust bearings and circulating-pump engine are provided with forced lubrication. The system comprises two oil pumps, one oil cooler of 202.33 square feet of cooling surface, one oil-cooler circulating puinp,* one oil drain tank of 200 gallons capacity, an oil-settling tank of similar capacity and the necessary piping and fittings.

The system functions as follows : The oil pumps draw oil from the drain tank and deliver it via the oil cooler to the various parts to be lubricated at a pressure of about 15 pounds. Macomb strainers are fitted in the pump suctions and a bypass arranged around the oil cooler. After the oil has passed through the bearings it is caught in troughs formed in the bearings bases and drained by gravity back to the drain tank, whence the cycle is repeated. Lock cocks are fitted at each bearing for regulating the supply, and sight glasses for observing the oil flow are fitted in the drain from each bearing. A thermometer is also fitted at each sight glass to show the temperature of the oil leaving the bearings. The oil pumps also discharge to a settling tank through a branch off the main discharge. The tank is provided with a steam coil to assist in settling the oil, and is drained back into the system by gravity, or drawn off by the pumps, a Macomb strainer being fitted in the connection next to the tank.



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