IMPROVEMENTS IN VALVE GEAR FOR STEAM, GAS, AIR OR WATER ENGINES
Year: 1882

page_text: PROVISIONAL SPECIFICATION left by William Roger Dawe at the Office
of the Commissioners of Patents on the 25th May 1882.
WILLIAM ROGER DAWE of Castle Gate Grantham in the County of Lincoln
"IMPROVEMENTS IN VALVE GEAR FOR STEAM, GAS, AIR OR WATER ENGINES
"
The Invention has for its object improvements in valve gear for steam, gas, air
or water engines and relates to an improved arrangement of parts for communicating
a variable extent of motion to the valve by the governor in order to maintain as
nearly as possible a regular speed to the engine.
For this purpose I employ a slotted disc or link which is mounted with capability
of revolving upon a stud or pin fixed to a slide which is raised and lowered by a
link from the governor. This slotted disc or link has the slot extending across and
perforating it except at the centre where it is provided with a boss through which
its pin passes.
A die-block works in this slot and is attached by a pin at the lower end thereof
to the eccentric rod, by a pin at the upper end to the valve rod and by a pin at
the centre thereof to a radius rod which controls its position with regard to vertical
movement.
When the slotted disc or link is at its normal position and the engine is running
at its normal speed the centre pin of such disc or link is maintained by the governor
exactly behind the pin of the radius rod attached to the die block, that is the two
axes are on the same line, and the motion of the eccentric is transmitted by the
disc or link revolving through a certain arc and giving to the valve rod the motion
imparted to the other end of the lever or die block by the pin at the lower end
thereof so that the valve has its normal travel; but on the speed of the engine
increasing the centre pin of the disc or link is raised by the governor and as the
die block is constant in position the pin at the upper end of that block approaches
the centre of the disc or link and at the same time the pin at the lower end thereof
recedes and the leverage of the upper arm of lever being decreased and that of the
lower arm thereof being increased the motion given to the lower pin of the die
block by the eccentric is imparted by the pin at the upper end thereof in a smaller
ratio, and the travel of the valve is thus shortened and in an extreme case supposing
the upper pin of the die-block were to correspond with the centre pin of the slotted
Di Q71

page_text: disc or link the eccentric rod would merely cause the said disc or link to rock on
its centre pin and no motion would be given to the valve rod.
On the speed of the engine becoming reduced the governor allows the slotted
disc or link to fall and the reverse action takes place the lower arm of the lever
being decreased in length and the upper arm increased, the motion given by the
lower pin is magnified at the upper pin and the valve travel correspondingly
lengthened.
The valve used may be the ordinary "locomotive" D slide valve, or a cut-off
valve on the back of a slide valve, or other suitable valves may be used,
The eccentric may be re-placed by a crank or cam.
A balance weight to disc, link or governor may be used.
The slotted disc or link may be replaced by a link of solid slotted H or other
section and may be of curved or straight form and the die block varied to suit
link and the distances or leverages may have any ratio or lengths.
The travel of the valve may be adjusted while the engine is running by a right
and left hand screw and nut used to increase or decrease the length of the link
connecting the governor with the slide.
Any kind of governor may be used and the slide and slotted disc or link may be
used as the weight of the "Porter" governor.