Monday, 30 September 2013

TWIN QUADRUPLE EXPANSION ENGINES.

If one peruses the literature on the Waratah, there are two clearly contradictory pieces of information about the Waratah's steam engines. Wikipedia quotes the following:

"power: 5 x steel boilers

Propulsion: 2 x 4-cylinder triple expansion reciprocating steam engines

Speed: approximately 13.5 kn (25.0 km/h; 15.5 mph) service speed."

If one looks at the Lloyd's report, it is as follows:

"She was fitted with two sets of reciprocating compound quadruple expansion direct-acting vertical inverted engines, with five steel boilers having a working pressure of 215 lbs., and developing 548.4 nominal, 5,400 indicated, horse-power."

"Her speed was 13 knots. Engines and boilers were also by Messrs. Barclay, Curle."

"The quadruple expansion engines with 8 cylinders of 23, 32 1/2, 46 1/2 & 67 inches diameter each pair; stroke 48 inches;
1,003 nominal horsepower;
5 single ended boilers;
20 corrugated furnaces; grate surface 376 sq. ft.;
heating surface 14,967 sq. ft"

A compound steam engine has more than one cylinder, and as stated in the Lloyd's report, there were 4 cylinders per engine (twin engines). The cylinders were graded according to diameter which translates into steam pressure differences and a gradient between the cylinders, thus creating a sequence of the steam expansion =  four separate stages.

The Waratah had four (quadruple) expansion cylinders, not three (triple). Built by Alexander C. Kirk at Govan in Scotland, this type of steam engine was first used in the SS Aberdeen, 1881. Direct acting means that the cylinders were connected directly to the crankshaft via the piston rods or connecting rods. The cylinders (inverted) were directly above the crankshaft similar to the standard internal combustion engine, except for the fact that a steam engine's force in the cylinders is both up and down - double acting. These vertical engines were sometimes referred to as 'hammer' engines.

By 1908, vertical steam engines predominated in marine vessels. These direct-acting engines were 40% lighter than the preceding formations (beam or side-lever engines), and required smaller engine rooms.  However, they were prone to wear and tear and required higher maintenance.Vertical engines became so popular in marine propulsion during the 19th century that they required further nomenclature eg. compound, triple or quadruple expansion etc.

Efficiency, maintenance costs and speed improved with the technology. The engines were constructed in such a way that the rear or aft cylinders were high pressure (Waratah: 23 inch diameter) graded to lowest pressure fore (Waratah: 67 inches). One of the advantages of this system is that the low pressure cylinder could be disconnected when the vessel required less power, allowing the high and intermediate power cylinders to be run together as a compound engine, more economically.

"It should be noted that the term "vertical" for this type of engine is imprecise, since technically any type of steam engine is "vertical" if the cylinder is vertically oriented. An engine described as "vertical" should therefore not be assumed to be of the vertical inverted direct-acting type unless the term "vertical" is unqualified."

The Waratah was capable of taking about 2,100 tons of coal in the permanent bunkers, to feed the five boilers of the steam engines, an average of 80 tons consumption per day. Her power output of 5400 ihp was relatively under powered for a ship of this size - I shall explore this further in coming posts by comparing with other period steamers.


triple expansion engine


cross section standard steamship

vertical triple expansion steam engine



cross section engine room and boilers

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