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Mechanism of Steam Engines Part 5

Tham khảo tài liệu 'mechanism of steam engines part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 46 MECHANISM OF STEAM ENGINES VALVE DIAGRAMS 47 to position OM in Fig. 55 E is the actual position of the eccentric center. Then ST is the valve displacement if the valve has harmonic motion. EST i8o ọo a 1 90 a 0 In Fig. 55 BOD a Ớ . Therefore OBD 90 a Ớ . Hence OBD EST and since OB SE the triangles EST and OBD are equal. Therefore BD ST. Referring still to Fig. 55 if L is equal to the head-end steam lap and N the head-end exhaust clearance A h is the crank position for H.E. admission. Ch is the crank position for H.E. cut-off. Rh is the crank position for H.E. release. Kh is the crank position for H.E. compression. CHAPTER IV TYPICAL PROBLEMS ON THE SLIDE-VALVE ENGINE 41. The following examples will serve to illustrate the manner of studying the action or design of a slide-valve mechanism certain proportions of which are known. An understanding of the constructions here given will also give more familiarity with the slide valve its possibilities and its limitations than could be obtained in any other way. The student should constantly guard against becoming so involved in the geometry of the diagrams that he loses sight of the real mechanism. 42. Given Ratio connecting rod to crank 4 to I. Ratio eccentric rod to eccentricity 6 to I. Valve to be a plain D valve driven direct. Angle between crank and eccentric known eccentricity known piston positions for cut-off and compression known for both ends. To find Laps leads and piston positions for release. Here the ratio of eccentric rod to eccentricity is so small that the valve moUon departs materially from harmonic motion. Consequently any one of the diagrams which depends upon harmonic motion of the valve would be inaccurate in this case. The valve ellipse however takes into account all the irregularities and can be used. The first step will be the plotting of the ellipse. This is shown in Fig. 58 where the valve displacements are taken from Fig. 57. The method of plotting the ellipse should be clear from the .