Mechanism of Steam Engines Part 11

Tham khảo tài liệu 'mechanism of steam engines part 11', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 134 MECHANISM OF STEAM ENGINES by adjusting the lengths of the steam and exhaust links. The following table of laps and leads for various size Corliss engines is taken as representative of good current practice TABLE OP LEADS AND LAPS FOR DIFFERENT PISTON DIAMETERS r- 1 Pteoq Diameter lacfaea Lead Steam Lav T Eehamt CSeaeaoce ị i S-L4 1 A . i A 14-20 A A A 1 20-26 A 1 A 26-32 A A 3 -3 A 1 i 38-44 A A A Place the engine on either dead point the gear being connected up. Turn the eccentric on the shaft until it is about ninety degrees ahead of the crank and then turn it ahead slowly until the steam valve has the proper lead. Fasten the eccentric on the shaft and turn the engine to the other dead point. If the previous work has been carefully done the lead on this end should be the same as on the other. If it is not it may be made so by changing the length of the steam link this of course affects somewhat the steam lap but as cut-off is not dependent on the steam lap this is not a serious matter. Next block the governor about haff-way up and move the engine ahead until it reaches the point where cut-off is desired for normal lead. Adjust the length of the proper governor reach rod until the stop releases the valve. Repeat for the other end. Lastly with the governor in its lowest position and with the wristplate in one extreme position adjust the safety stop so that the hook-block will not be caught when the wrist-plate swings back. Repeat for the other extreme position. 104. Valve Setting with Steam. Very often valves are set by running the engine under steam and taking indicator cards. To the experienced man the indicator card tells just what is wrong with the valve adjustment and changes are made until the best possible card is obtained. It is of course necessary to set the eccentric in its approximate position and to roughly adjust the valve gear before the engine will turn over under steam. VALVE SETTING 135 However carefully the valves have been set without using

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