Referring to the point of cut off finally, it is determined upon by a
governor of the fly wheel type. The eccentric is loose about the
shaft, and arms projecting therefrom are connected by other arms to
the extremity of an arm upon which is mounted a weight, and which is
attached to the spokes of the fly wheel, or special governor wheel in
this case, and which is fastened to the crank shaft. As the speed
increases through throwing off a portion of the load the governor
weights fly out, and this movement is transferred through the lever
connections to the eccentric, causing it to be turned ahead, and the
manner hastening the movement of the cut off valve on its seat and
causing it to reach and cover the edge of the steam port earlier in
the stroke. This engine was the pioneer in governors of this
character, the advantage being, in addition to its necessity for the
work of turning the eccentric ahead or back, that the liability of the
engine to run away, as very often happens from the breaking of the
governor belt or a similar cause, was not possible.
The cut off valve has a travel considerably beyond the edge of the
steam passage after the valve is closed, and this has one advantage,
that the valve is less liable to leak, and to this must be added the
loss from the friction of this moving valve, and moving too in
opposition to the main valve.
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