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Ed wrote:

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I got a lot of my questions on boilers answered, thanks.

Now, lets move down the piping to the steam turbine. It is my understanding that high pressure steam turned the turbines at a very high RPM, 8,000 to 10,000 RPMs. Was the turbine speed constant at all ships speed?

No. It varied with the amount of steam admitted. This was with either direct drive (no gearing) or geared turbines.

I know the reduction gears were used to reduce the high shaft RPMs down to a propeller speed (about 185 RPMs for a SoDak at 28 knots, and 195-200 RPMs for an Iowa at 33 knots). But was the reduction gears the only thing the turbine drove?

For the main engine turbines, yes. The devices were consumers of what was called at least in the USN 'main steam,' the highest pressure and temperature steam produced by the boilers. The only other consumer of this steam were the Ship's Service Steam Generators (SSTGs), AND, the reducing stations that reduced the pressure to that needed by the many auxiliary devices in the plant. By comparison these 'consumers' used very little of the boiler output, and did not need the high pressure/temp steam of the main engines and generators.

The SSTGs can be considered miniature main engines, with their own turbine, gearing, lube oil pumps and condensers.


Did they also drive other accessories like generators? Why did a turbine need to turn so fast? How many of the turbine sections drive, just the first stage, or all stages? Was the steam, after it drove the turbine blades still high pressure? What was done with the steam after it exited the turbine? Was the steam still useful in other applications?

Turbines operated more efficiently at high rpms. The gearing solved the dichotomy between their speeds and those of the propeller shafts. The next step up in the turbine business from the original Parsons design of the early 20th century was gearing, to make more efficient the 'direct drive' arrangement.

USN plants like SoDak had two turbines per shaft, an HP and LP turbine. The former was smaller and got the steam from the boiler first, exhaust from it passing through a cross-over pipe to the LP turbine. Steam coming out of the HP had traded some of its thermal energy to the kinetic energy necessary to drive the gearing. The LP turbine's blading was larger as a consequence, and its exhaust entered the main condenser at about 100 deg F, compared to 850 deg F (max) as it entered the HP turbine. These two tubines set alongside each other forward of the gearing.

Exhaust steam from the main engines and SSTG entered sea-water cooled condensers directly under the LP turbine for the engines, and nearby the SSTGs for them. I've addressed the other steam consumers in the plant - exhaust steam from these devices (forced draft blowers, condensate pumps, main feed booster pumps, main feed pumps, fire and flushing pumps, and a variety of non-rotating devices) went into a piping system know as 'auxiliary exhaust' which led to the Deaerating Feed Tank. This tank performed two other functions; is served as a surge tank when the ship was changing speeds and the water balance in the plant was changing with steam demand), and it 'dearated' the feed water to protect boiler tubes from oxygen pitting. Condensate pumps taking water from the previously-mentioned condensers also discharged into the DFT.

By naming convention, all that condensed water prior to the DFT was 'condensate' and all after it was 'feed water.' The main feed booster pumps took suction from the DFT and provided a positive suction head to the main feed pumps. The latter pushed the feed water into the boiler against the boiler's operation pressure.

This is probably more than you wanted to know, and does not address so-called 'steam cycles' in other plants in the USN or other navies.

Ed