While valves should be set for equal leads, which will make
the two cutoffs different, at times it may be advisable to set a valve for
equal cutoffs. First. Set engine on head end dead center.
Second. Shift the eccentric until it is as near its correct
position as can be estimated.
Third. Give the valve the desired lead on the head-end. Now
turn the engine over in the direction in which it is to run until cutoff occurs
on the head-end.
Fourth. Measure the distance the crosshead has moved and make
a chalk mark on the guide.
Fifth. Turn engine on over past crank dead center until cutoff
occurs on the crank end. Measure the travel of the crosshead from crank-end
dead center. If the distance is same as for the head-end, the eccentric is-in
the correct position.
Sixth. If the distances are different change the valve rod
lengths until cutoff occurs at same distance from the ends.
Seventh. Turn the engine to the head-end and give the valve
the desired lead by shifting the eccentric. Test the two cutoffs again. If
they are not equal adjust the valve rod length again. Turn over to head-end
and shift eccentric to give the desired head-end lead. Try again. Finally
check the crankend lead to see that it is not excessive... Best Method of
Setting D Valve
The above methods call for considerable shifting of the engine
and adjusting of the valve rod and eccentric. The method which follows eliminates
all this trouble and is recommended in all cases where exact setting is desirable.
Method. The valve should be lifted off its seat and a template
made of the valve seat and of the valve. This is done by... Setting Riding
Cutoff Valve
Many engines especially those driving air compressors make
use of a valve having a secondary valve riding on top of the main valve and
whose function is to control cutoff by covering the steam port in the main
valve.
The lead, exhaust and compression are completely controlled
by the main valve which, as indicated in the diagram Fig. 28, consists of
an ordinary D slide valve that is extended in length with two admission ports
P formed through it, each equal in width to the ports in the cylinder face.
The main valve is driven by an eccentric, in the ordinary way, and... Setting
the Corliss Valve Gear
The first step in setting a Corliss valve gear is to see that
the motion of the eccentric is properly transmitted to the wristplate. The
rocker arm should vibrate to equal distances on each side of a vertical line
passing through the center of the rocker fulcrum pin C. In Fig. 34 the distances
AD and DB should be equal. To check this a smooth board should be placed on
the floor under the rocker arm. The arm should be placed in a vertical position
and the plumb-bob dropped to just clear the board and a mark made. The engine
should be turned over...