THE ACTION OF STEAM.
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How Steam is Employed to Develop Power in the Compound Engine of an Over-type Steam Wagon.
THE growing popularity of the overtype steam wagon and the great extension of its use as the general purpose wagon On heavy transport work calls for a clearer understanding of 'the principal duties of its construction. This article briefly describes the action of the steam in the cylinder, the Clayton being taken as an example of an efficient piston-valve engine. Outwardly the cylinder appears to be a simple casting, lint, as a matter of fact, is the most intricate part of the vehicle, demanding experience, skill, and scientific knowledge in both its design and construction. As the power generator, the heart of the engine, an, efficient
cylinder is of first importance. The passages must be ample, yet/not too large, and with as few bends tand corners as possible, so as not to hinder the free flow of the steam.
The illustrations show details of a twocylinder compound type—that is, one With high-pressure and low-pressure cylinders, both cylinders being fitted with piston valves. In practice, the piston type of valve has shown less wear than the flat D-type valve fitted on some engines.
Referring to Fig. 1, steam from the boiler enters the opening at "A," and is free to flow round both cylinders and piston valves, through the opening " B "
and roand the steam easing " " at the top. The passage " B " between the cylinders is kept as narrow as possible (as will be seen in Fig. 2), and so prevents any tendency of water, due to priming, reaching the stop valve. The stop or steam-regulating valve is placed at the highest point on the cylinder to ensure dry steam only entering the cylinders. The valve itself works between the guides shown at " 0," the spindle being, of course, led to a convenient position by the driver's)qest. It is usually of the flat type.
With the engine working compound, die action of the steam is as follows ;— The stop or regulating valve is pushed over, uncovering a port which a/tin:tits steam into passage "D " (see Fig. 2); that is, to the centre of the piston valve. The piston is, of course, attached to the link motion which causes the valve to move forward and backward, admitting steam alternately to the front and back ends of the cylinders through passages " E " and "F," and exhausting at both ends " C-" alternately. This exhaust steam, after it has done its work in the hi.p. cylinder, flows through the passage "iG" along passage "H" (Fig. 2) to the centre of the 1.p. steam chest, passing on its way through the double
high-pressure valve "J" (Figs. 1 and 2). The link motion again regulates the steam admission through passages " K " and " L " into the 1.p. cylinder (Fig. 2). After having done its work, it is exhausted back through the passages "K" and " L," and is free to travel along passage " M " into the exhaust pipe, thence through the silencer and up the funnel.
• That is, when working compound, the same steam is used in both cylinders, which is a great economy when compared with the two-cylinder, high-pressure type of engine. illhte great feature of the steamer, and of the overtype wagon in particular, is its easy flexibility and enormous reserve of power (in many cases as much as 100 per cent.). This is obtained by working both cylinders with high-pressure steam in the following manner.
The stop valve is set for "double high pressure," and, in addition, the double high-pressure cock is pushed over, so as to prevent the h.p. exhaust steam from entering the 1.p. steam chest.
Live or h.p. steam is admitted to the h.p. passages in the usual way and, in addition, the stop or regulating valve uncovers a small port at N " (Fig. 3), which allows the steam to enter passage "P "and so pass to the centre of the 1.p. piston valve. It is then admitted to and exhausted from the 1.p. cylinder in the manner already described. The h.p. steam, after having done its work in the h.p. cylinder, passes along passage " H " but, in place of entering the 1.p. steam chest, is diverted by the double high-pressure plug direct to the exhaust pipe and so up the funneL This fitting should, of course, only be used in emergencies, as in starting up on a steep incline with load or when negotiating very difficult ground.