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DD-47 Aylwin - Machinery

The propelling units are two Cramp-Zoelley turbines and two compound reciprocating engines. These are twin-screw vessels with combinations of turbines and reciprocating engines. The turbines are of the Cramp-Zoelly type, to be used when speeds greater than 17 knots are desired. For cruising speeds below 17 knots there is on each shaft a reciprocating engine.

The turbines are of the compound impulse type arranged on two shafts and designed to develop 16,000 S.H.P. at about 620 revolutions per minute. The reciprocating engines, two in number, are of the vertical, inverted, two-cylinder, compound type located just forward of the turbines. These are brought into use by means of a power-controlled clutch of the friction type. This clutch is so designed that the engines are capable of being connected or disconnected without slowing down and is interlocked with the maneuvering valves so that steam can not be admitted to the ahead or astern turbines until the reciprocating engines are disconnected. There is also fitted a governor valve, which secures the reciprocating engine from running away in case the clutch should become disconnected. The turbines consist of two essential parts : the fixed part or casing and the moving part or rotor. Within the casing are secured the fixed diaphragm plates, the intermediate-guide blades and the expanding-guide blades, and on the rotor are secured the discs and drum carrying the moving blades. The rotor is supported at the forward and after ends of the casing by bearings secured thereto.

• Full Speed Ahead. - Steam at full pressure is admitted to the full-head chest and allowed to expand through all the stages of the turbines until finally exhausted into the condensers. The astern turbines under these conditions are running idly in a vacuum.
• High Cruising Speeds.- At these speeds the steam is admitted to the intermediate-ahead chest, throttled to suitable pressure, and passes through the same paths as under full-speed conditions.

• Low Cruising Speeds. - The reciprocating engines are used in connection with the turbines at these speeds. Steam is expanded through the reciprocating unit from which it is exhausted into the reheater, thence to the intermediate-ahead chest, through the turbines and into the condenser. The heating agent in the reheaters is the exhaust steam from the reciprocating-engine cylinder jackets.
• For astern motion at all speeds the astern turbines alone are used, and for maneuvering the turbine units only are in use.

An interesting feature of the design of machinery in this class of boat built at the Cramp's yard is the "change valve." By means of this valve the supply of steam to either of or both the main and intermediate-ahead chests in the interests of economy or regulation of speed, may be regulated.

There are two lines of shafting, each in seven sections, namely, the crank shaft for the reciprocating engines ; the intermediate shaft connecting the reciprocating and turbine units ; the rotor shaft, within the turbine casing, supported by the thrust bearings : two sections of line shafting, supported by spring bearings; the stern-tube shaft, supported by the stern-tube bearings, and one propeller shaft, supported by the strut bearings. All shafting is of Class "A" steel forging.

There is one main bearing at each end of each turbine, the pedestal of which is cast with the turbine casing. The bottom brass is arranged to roll out without lifting the shaft after the weight of it has been taken up with the lifting gear, and the top brass to come off with the cap.

All turbines are provided, at the forward end, with thrust bearings, carried in the cylinder casting. It is halved, and so designed that the upper half will take the steam thrust and the lower half the propeller thrust. The collars are of brass, semicircular in shape, let into bushings and caulked into place, fitted into corresponding collars on the shaft. There are four spring bearings for the line shafting, of the self-oiling type, secured to foundations built upon the frame of the ship.

Each shaft is fitted with hand-operated turning gear, carried by brackets on the turbine casing. It consists of a worm wheel upon the shaft, meshing with a worm operated by a ratchet wrench arranged so that the gear may be readily connected or thrown out. An efficient hand-operated gear is provided for the main turbines.

There are two three-bladed propellers. The starboard propeller is right-hand and the port is left. The hubs and blades are of manganese bronze, cast solid. The blades are true screw machined to pitch and polished. An improved type of Gary-Cummings torsionmeter is provided for each line of shafting, for ascertaining the shaft horsepower developed at the various speeds.

There are two main condensers of elliptic-triangular section, located outboard of the low-pressure turbines. They are of the bent-tube type, with the tubes expanded into the tube sheets. There are two Blake vertical, twin, beam-bucket air pumps, located in the auxiliary room just abaft the forward bulkhead, and immediately inboard the two shafts. For each condenser there is a single-inlet centrifugal circulating pump, driven by a single-cylinder inclosed reciprocating engine. These pumps are located on the extreme outboard sides of the engine room, just forward of the condensers.

There is located in the auxiliary room on the port side abaft the forward bulkhead a feed and filter tank of 874 gallons capacity. In the top of the tank is located the filter tank of 166 gallons capacity, so arranged that the water is admitted to and delivered from the top of the chambers, thus keeping them filled with water and the filtering material submerged. A three-quarter-inch connection is provided for the admission of lime-water solution.

Located in the port forward corner of the engine room are two Blake vertical simplex, piston, double- acting pumps, 15 inches X 10 inches X 16 inches. These pumps are provided with suctions from the main feed tanks and discharge to the boilers through the feed heaters or through by-passes.

The auxiliary condenser, of 256 square feet cooling surface, is in the port after corner of the auxiliary room. Immediately below, and connected to the condenser, is a Blake (5 inches X 8 inches X 8 inches X 7 inches horizontal, simplex, combined air and circulating pump. The condenser is connected to all the machinery through the auxiliary exhaust line.

The main bearings, thrust bearings and main circulating-pump engines are provided with forced lubrication. The system comprises two oil pumps, one oil cooler of 175.2 square feet of cooling surface, one oil-cooler circulating pump, one oil-drain tank, an oil-settling tank, and the necessary piping and fittings.

The system functions as follows : The oil pumps draw oil from the drain tank and deliver to the bearings via the oil coolers at a pressure of about 15 pounds. Macomb strainers are fitted at both ends of the pump and a by-pass is arranged around the oil coolers. Troughs formed in the bearing bases catch the oil, from which it is led by gravity to the drain tanks. At each bearing are fitted lock cocks for regulating the supply of oil, and sight glasses for observing the flow of oil. Thermometers are also provided at each sight glass, to show the temperature of oil leaving the bearings.

The oil pumps discharge to a settling tank through a branch of the main discharge. A steam coil is provided to assist in settling the oil, which is drained back to the system by gravity or drawn off by the pumps, a Macomb strainer being fitted in the connection next to the tank.