Improvements in Valve Reversing Gear for Steam Engines and the like, including Locomotive Engines.
Year: 1895

page_text: Date of Application, 29th Mar., 1895
Complete Specification Left, 5th June, 1895-Accepted, 20th July, 1895
PROVISIONAL SPECIFICATION.
Improvements in Valve Reversing Gear for Steam Engines and the
like, including Locomotive Engines.
THOMAS HUNTER THOMS The Beeches Didsbury, Lancashire Engineer. I do
hereby declare the nature of this invention to be as follows:-
My invention has for its object the simplification of the valve reversing gear for
steam engines and the like where at present what is ordinarily termed a link motion
is now used for regulating the distribution and the expansive working of steam
supplied to the cylinder.
In the construction of this valve reversing gear, instead of using two eccentrics
as are usually employed for the working of a link motion, one eccentric only. is
necessary for each valve, and where a pair of engines are driving on the same shaft
or axle as in the case of a locomotive engine, both valves can be actuated
simultaneously and in the same proportion.
Having determined the necessary amount of travel required for full forward and
full backward gears, the amount of eccentricity and angle for lead can be fixed as
for a simple engine, only the eccentric sheave is made to travel across the shaft or
axle from forward to backward gear & vice versa this being arranged according to
the dimension of the shaft or axle and the amount of transverse travel to allow for
positions of eccentric sheave in full forward and full backward gears.
The part of
the axle or shaft on which the eccentric sheave has to traverse is made of square
or oblong section so that twisting is prevented which is of the utmost importance
for the free travel of the eccentric sheave on the axle.
For the required purpose of actuating the eccentric sheave I employ a sliding
disc with sleeve-bearing on the shaft which is worked by a clip or strap which
permits the free revolving of the disc with the axle or shaft, (the pathway for the
sleeve on the axle or shaft being made of square or oblong section also).
The disc is made to slide along the axle or shaft by levers attached to studs or
pins on the clip or strap, and where as in locomotive engines a variation from the
working of the springs takes place, short links are introduced between the levers
and the clip or strap to overcome the rise and fall of the axle. On the sides of
the disc are bosses for coupling to ends of connecting links which at the other end
are attached by pins or bolts to bell crank levers pivotted on shaft, the part of
shaft where pivots are fixed being increased in strength to allow for the holes for
pivot studs; the bell-crank levers are at the right angled ends connected to sliding
blocks or dies in the eccentric sheave, which operate when moving the eccentric
transversely on the shaft. Any thrust that may arise on the eccentric is taken
first on the sliding blocks, transmitted to the bell-crank levers, and carried on by
the links to the sliding disc which is held in position eventually from a reversing
shaft by a reversing handle, and notched sector, reversing screw, or fluid
reversing gear as may be considered most convenient in its arrangement on the
engine.
28th March 1895.
THOMAS HUNTER THOMS,
The Beeches, Didsbury, Lancashire, Engineer,

page_text: Figs. 5, 6 and 7. Sectional end elevations shewing the three positions of the
eccentrics.
In the construction and arrangement of this valve reversing gear with single
eccentrics A the axle or crank shaft B is formed with flat surfaces at b and b'.
Upon the flat surfaces the eccentrics A are fitted so as to slide across or trans-
versely to the longitudinal axis of the axle. For the purpose of guiding the
eccentrics in their travel side collars are left or formed of sufficient width to
project past the flat surfaces and so obviate any likelihood of the eccentric
becoming twisted
on the shaft while being traversed from one position to
another. The axle is also left of a stronger section by a continuation of the
projecting collars which permits of a reduction in area for the pivots or fulcrum
studs e.
The centre part of the axle b' is also preferably made with flat surfaces or what
is generally termed square or oblong in section in place of the ordinary round at
that part. Upon this square or oblong portion on the axle is fitted a sliding
disc which regulates the position of the eccentrics when working in full gear
forward or backward or for any degree of expansive working in either gear.
The eccentrics A which are single for each side of the engine are each provided
with an oblong slot a through which the axle passes and which is fitted on to the
flat surface b upon which it slides. The slot a is of sufficient length to allow of the
full travel of the eccentric from full forward to full backward gear.
Each eccentric is fitted with two slide blocks D one placed at either side of the
slot a.
These blocks are made a sliding fit in holes provided for them and have a
sliding movement from one side of the eccentric sheave to the other to compensate
for the radial movement of a bell crank lever E connected thereto, by which the
eccentric is caused to traverse across the axle from one position to another.
The bell crank levers E are pivoted upon pins or studs e secured to the axle B
and are connected to the slide blocks D of the eccentric by the pins d. The other

page_text: ends of the bell crank levers E are connected through links F with the sliding
disc which is fitted upon the central part b' of the axle B. The sliding disc C
forms a connection to actuate both sides of the engine simultaneously when two
cylinders are driving on the same axle and the links Fare connected to it by the
pins which pass through bosses c on the sides.
The cranks are represented at K and L.
The sliding disc C is provided with a sleeve c¹ bearing on the axle B to give
greater bearing surface and is caused to slide laterally on the axle by a clip
ring or strap G which encircles it and also permits of its revolving freely with
the axle. The sliding disc is actuated by the shaft H and levers J through
the connecting links attached to pins g on the clip ring or strap G and any
degree of movement can be transmitted to alter the eccentrics for any position in
either gear.
By the insertion of the links between the levers J and the clip ring or
strap G any movement is permitted between the axle and the body of the
engine which may arise from the working of the springs when the reversing
gear is applied to a locomotive engine without any appreciable change taking place
in the valve gear.
The actuating shaft H is coupled to a reversing handle with sector or other gear
as may be required.
When the engine is running any thrust or pull strain which may arise on the
eccentric sheaves A is transmitted from the eccentrics to the sliding blocks D and
through them to the bell crank levers E and sliding disc C.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed, I declare that what
I claim is :-
1. A reversing valve gear comprising a single eccentric moving across the crank
axle or shaft fitted with sliding blocks and actuated or controlled by bell crank
levers pivoted on the axle substantially as described.
2. In reversing valve gear the combination with the single eccentric formed with
a slot upon which it traverses across the axle or crank shaft from side to side of
sliding blocks fitted therein with a movement from one side of the sheave to the
other pivoted bell crank levers connected thereto and a sliding disc capable of
lateral movement upon the axle substantially as described.
3. A reversing valve gear having the several parts constructed and arranged in
combination substantially as described and shown.
Dated this 4th day of June 1895.
WM. P. THOMPSON & Co.,
6, Bank Street, Manchester, Patent Agents.