The Application of Superheated Steam to Locomotives
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The Application of Superheated Steam to Locomotives |
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There were 2 distinct types of superheaters for locomotives, invented by Dr. Wilhelm Schmidt.
No differences exist between these two types with regard to economy or efficiency, but there were advantages of the smoke tube type over the smoke box type, like water distribution, weight, accessibility and simpler design. An illustration of a smoke tube superheater element is depicted below.
The smoke tubes were located in the upper part of the boiler, as shown in Figure below.
They were between 100 mm (4 inch) and 133 mm (5-1/2 inch) in diameter and expanded into the firebox and into the smoke box
tube plate. A double U-type superheater element was inserted into each one of the smoke tubes, which then was bolted to a
two-section header at the smoke box end. One section represented the steam inlet into the superheater tubes, while the other
half served as the superheater outlet side. An earlier design consisted of two separate single U-tubes, which had larger heat
exchange surfaces and consequently higher metal temperatures. They therefore had a shorter life span.
The superheater elements were made of seamless steel tubes.
Function of the Superheater - The combustion gases divided into
two streams, one passing through the ordinary boiler tubes and the other through the larger smoke tubes. The heat carried
by the gas in the smoke tubes was partially transferred to the water surrounding those tubes, and partially to the steam contained
in the superheater tubes. Dampers of different designs controlled the gas flow through the smoke tubes, and by this the steam
temperature. As long as the regulator was shut the dampers were kept closed by either a counter weight or by a spring, but
immediately the steam is turned on, the damper is gradually opened in a controlled manner to control the steam temperature.
The controller consisted of a piston in a cylinder and was controlled by steam pressure. To avoid overheating of the superheater
tubes the controller prevented the combustion gases from entering the smoke tubes. Method of cleaning – Soot and ashes could be removes from the large smoke tubes and from the
superheater elements inside them by means of either steam or compressed air through a hose and nozzle. This operation was
preferably carried out from the firebox, but if necessary it could also be done from the smoke box. Cleaning by brushes was
possible, but cleaning by steam or compressed air was a much faster method. Special Advantages – The main features of the new and improved type was its thorough intercheangability
and accessibility. Each individual superheater element could easily be removed and examined without disconnecting the whole
arrangement, by merely loosening a single nut, which kept the superheater tube in position. Adaptability – This type of superheater could be adapted for use on either new or existing locomotives.
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