66 THE SLIDE VALVE PRACTICALLY CONSIDERED. BY N. P. BURGH, ENGINEER, AUTHOR OF 66 A TREATISE ON SUGAR MACHINERY;" 66 A POCKET BOOK OF PRACTICAL RULES FOR DESIGNING ETC. ETC. ETC. LONDON: E. & F. N. SPON, 16, BUCKLERSBURY. 1865. PREFACE. THE relative position of the engineer to the steam engine may be said, with some truth of comparison, to be analogous to that of the medical man and his patient. Of all the details (so to speak) of the human body, the heart is the most important. The same may be said of the slide valve, in comparison with the remaining details of the engine. In either case the defective action of the heart or valve impedes the progress of the whole. The present work is intended by the author to enable the student and interested observer to clearly understand the use and action of the slide valve. The rules relating to the equilibrium slide valves have been carefully digested; that portion relating to the "width of the large bar" is, perhaps, the most important of all, while the simplicity is perfect. The delineation of the eccentric circle should he well studied, it being remembered that from it the slide is proportioned. The angles assumed by the cranks at given grades of expansion are matters too often disregarded by the pupil and young engineer. It is not usually appreciated that the arc passed through determines the lap of the valve. In no case whatever should a valve be designed without first considering the direction of the crank pin, and the amount of expansion required. The proportion of lap to width of opening or port can only be obtained by the means alluded to. The lead of the slide valve has been duly considered in this work. The author would impress that the true versed sine and radius of the arc of supply steam can only be attained, by noticing the lead. The time for supply, expansion, exhaustion, and compression has been fully explained, so that its value and defects will be apparent. The delineation of the crank circle has met with due attention, and will be found of utility in proving the actual consumption of the steam at each stroke of the piston. In the chapter relating to "General Observations" will be found hints worthy of notice. The proportions alluded to are deduced from the best results. The index will be found lucid and copious, so that the allusion made to any detail in requisition is rendered perceivable per se. The author has carefully avoided theorizing on the subject on which he treats; all his remarks have been deduced from practical demonstrations -assumptions have not been admitted-therefore the data given will be found exact. THE SLIDE VALVE PRACTICALLY CONSIDERED. CHAP. I. ANTECEDENTS OF THE SLIDE VALVE AND STEAM PORTS IN THE CYLINDER. THE steam engine of the past and that of the present widely differ in the consumption of the fuel, or rather steam, per indicated horse power. Twenty years ago, eight to ten pounds of coal per actual horse power was deemed a good result, while in the present day two and a half pounds of coal per horse power is considered but a fair attainment. This great reduction is due to two causes,―perfection of manufacture and arrangement, and the application of natural laws. The friction due to the surfaces in contact of all bodies are alike in principle. The slide valve may be said to be a body moving on a given area, the pressure of the steam being the load on the same. An idea of the friction imposed can be attained by |