Titanic’s two sets of reciprocating engines were four-cylinder triple-expansion designs balanced by the Yarrow, Schlick and Tweedy system. The cylinder diameters were 54 inches (137.2cm) and 84 inches (213.4cm) for the high pressure (HP) and intermediate pressure (IP) units respectively, and 97 inches (246.4cm) for each of the low pressure (LP) cylinder pair; all shared a stroke of 75 inches (190.5cm). It is interesting that each engine featured two LP cylinders according to the balancing system, rather than two IP units, as was more common for four-legged triple-expansion engines. An LP cylinder was arranged at each end of the engines. The typical steam conditions at the various stages were: HP cylinder inlet (215 lb/in2/394oF); IP cylinder inlet (78 lb/in2/322oF); and LP cylinder inlet (24 lb/in2/266oF).
Each engine developed 16,000 ihp at 75 rpm, with steam supplied at a pressure of 215 lb/in2 exhausting from the (four) LP cylinders of both engines to the single turbine at 9 lb/ in2 abs/188oF. A key element of the machinery was a huge changeover valve to direct the exhaust steam from the LP cylinders to either the main condensers or the turbine. The exhaust steam turbine was non- reversible, so manoeuvring the ship was executed using the wing propellers alone; once the ship was full away the turbine was brought into action.
The reciprocating main engines with an LP cylinder at each end were equipped with the traditional Stephenson’s Link motion valve gear but their size called for two D-type slide valves for each LP cylinder. The two valves worked side-by-side and were connected to a common crosshead operated by the usual double-bar links and eccentrics. For the other two cylinders of each engine, a single piston valve served the HP cylinder while two piston valves were fitted to the IP cylinder. Each engine drove its associated 28-inch (71.1cm) diameter propeller shaft through a thrust block of the old multi-collar type, incorporating no less than 14 collars to each thrust unit.
Aspinall-type governors fitted to the engines relieved the watchkeeper from the tiresome task of manipulating the throttle in rough weather, while a ball governor coupled to the turbine acted directly on the control gear for the changeover valves between steam engines and turbine. In the event of the turbine running away, the engine exhaust steam could be automatically directed to the condensers, thus shutting off the steam supply to the turbine. The Parsons multi-stage reaction
design
LP exhaust turbine developed around 16,000 shp when running at 165 rpm, an idea of its
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Plan of the main machinery rooms showing the two reciprocating steam engines forward of the Parsons low pressure exhaust steam turbine, which drove the centre propeller
Marine Propulsion I February/March 2012 I 17
overall size given by a rotor that was 12ft (3.7m) in diameter and almost 14ft (4.3m) long over the blade section. The complete turbine weighed 420 tons, of which the rotor accounted for 130 tons; its Parsons laced- type blades ranged in length from 18 inches (45.7cm) to 25½ inches (64.8cm). The 16½ft-diameter/22-ton central propeller driven by the turbine had four blades, while each wing shaft drove three-bladed 23½ft-diameter (7.2m)/38-ton propellers. The blades were bolted on to a cast steel hub, each secured by eight nuts and studs.
Providing a steam supply to match the
massive reciprocating engines was a challenge for the machinery designers, resulting in the provision of 29 boilers, each 15ft 9-inches (4.8m) in diameter and 20ft (6m) long. Six furnaces were incorporated in the 24 double- ended units and three furnaces in the five single-ended types. A total of 159 coal-fired furnaces were thus deployed, consuming around 850 tons of fuel a day.
No.1 boiler room, closest to the engines, housed the five single-ended boilers abreast; Nos. 2, 3, 4 and 5 boiler rooms each contained five double-ended boilers abreast; and right forward only four boilers would fit into the
Transverse section of the forward engineroom housing the twin reciprocating steam engines
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