. Railway mechanical engineer . Fig. 21 Fig. 22 See inside admission piston valves and direct 22. By using indirect rocker with this combination of rodsthe lead can be changed from decrease to increase. Valve Diafirnms—After determining the amount the leadincreases from full gear to mid-gear, it usually develops thatif both forward and back motion blocks are set line and linethe lead increases to such an amount that the port opening is so great even with the reverse lever on center that cut-off possible has been found to be nearly 30per cent, of the stroke. To overcome
. Railway mechanical engineer . Fig. 21 Fig. 22 See inside admission piston valves and direct 22. By using indirect rocker with this combination of rodsthe lead can be changed from decrease to increase. Valve Diafirnms—After determining the amount the leadincreases from full gear to mid-gear, it usually develops thatif both forward and back motion blocks are set line and linethe lead increases to such an amount that the port opening is so great even with the reverse lever on center that cut-off possible has been found to be nearly 30per cent, of the stroke. To overcome this defect set theback motion blind enough to reduce the lead to 5/16 in. inmid-gear, as determined by the Zeuner valve : Valve travel 6)4 in., lead increase 7/16 in. Jh/s^rc demrmines Leae^af any Poin\ befi^een R/flQear and Mia Gear. from line and line, lap 1J s i- To find the amount toblind, back up to produce 5/16 in. lead on center with for-ward motion line and line. See Fig. 23. For some unknown reason the lead does not increase asit should by using the indirect rocker with crossed rodsand it has been found necessary to set one class of Con-solidation type with 5/16 in. lead in the corner to have3/16 in. lead on the center, but this type of constructionis very old and only a few such engines are still in ex-istence. SOUTHERN VALVE GEAR All locomotives having Southern valve gear are designedfor constant lead, and should Ik- so set. It is not possibleto set this gear for variable lead and it should never beattempted. By adopting the process of elimination, provingone part at a time, the best results are obtained. All of the motion to the valve is imparted from the ec-centric crank. Since the lap and lead depends on the
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectrailroadengineering
