Complicating the issue is that not all 'taper' boilers were wagon tops -- the Niagara boiler, which has a straight top but is tapered on the bottom, is an example. (That locomotive also has carefully-designed separators ahead of its dry pipe to reduce problems with priming.)
Many later boilers have a 'reverse taper' on the rear portion of the boiler which follows the angle of the crown in the inner wrapper.
According to John H. White Jr., in his book "A History of THE AMERICAN LOCOMOTIVE, Its Development: 1830-1880", the main reason for the development of this design (known as the wagon-top boiler) was to provide more steam room. With more volume of steam above the water there was less chance of priming which could occur when a sudden release of steam would cause a pressure drop which would cause the water to boil more furiously, increasing the chance of water being carried into the dry pipe along with impurities in the dirty water often used in those days. He also mentions more weight on drivers and higher volume of water over the fire as other advantages.
I love this book: ISBN 0-486-23818-0
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"A stranger's just a friend you ain't met yet." --- Dave Gardner
Conical
Same me, different spelling!
How's that work?
Another thing is that the taper minimizes the effect of the change in water level when the engine negotiates upgrades and downgrades.
Wasn't the point to save weight? The boiler only needs maximum fatness at the point where steam enters the drypipe, so fat boiler there and skinnier elsewhere means less steel.
Some steam locomotives were built with tapered boilers... what was the advantage of tapered over cylindrical boilers?
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