IMPROVEMENTS IN THE METHOD OF AND APPARATUS FOR CUTTING OFF STEAM IN THE CYLINDERS OF STEAM ENGINES
Year: 1875

page_text: PROVISIONAL SPECIFICATION left by John William Shaw at the
Office of the Commissioners of Patents, with his Petition, on the
15th February 1875.
I, JOHN WILLIAM SHAW, of Longwood, in the County of York,
Cotton Spinner, do hereby declare the nature of the said Invention for
"IMPROVEMENTS IN THE METHOD OF AND APPARATUS FOR CUTTING OFF STEAM IN
THE CYLINDERS OF STEAM ENGINES," to be as follows:-
-
This Invention relates to certain improvements in the method of and
apparatus for cutting off steam in the cylinders of steam engines by
means of cambs and eliptical wheels.
In the cut-off valves that are ordinarily used great difficulty is
experienced in getting a pressure of steam in the cylinder, approaching
to the pressure in the boiler in consequence of not being able to give the
valves sufficient area in the opening of the port at the commencement
of the stroke of the engine, and when in the act of cutting off the valves
travel so slowly that the steam is what is commonly called wiredrawn.
The object of my Invention is to so regulate the supply of steam as to
secure the full boiler pressure or at any rate much nearer that pressure

page_text: than is possible with the cut-off valves in ordinary use. I accomplish.
this in the following manner:-To any convenient part of the engine I
fix my improved apparatus, which consists of a metal framework, in
which is centred a shaft with a spur or bevel wheel, as the case may be,
keyed on to one end of the same, to which motion is imparted from
crank or any other shaft by means of gearing and shafts in the most
convenient way to suit the varying circumstances of each particular case;
on to the first named shaft is secured a spur eliptical wheel gearing into
another eliptical wheel secured to a second or intermediate shaft, on to
which is secured a spur pinion gearing into a spur wheel keyed to a
shaft, which revolves in framework, to which is also keyed a tappet;
into the last named spur wheel is geared another wheel having the
same number of teeth centred and secured to a shaft revolving in
framework, to which is attached another tappet. When the piston of
the engine is at the proper position for having steam admitted, the first
named tappet which is revolving comes in contact with a lever, one end
of which is centred on a stud; at the required distance from the said stud
is a jointed rod, one end coupled in the usual way by means of pins to
tappet lever and the other to a lever that is secured to valve spindle;
when either of the tappets come in contact with tappet lever the
cliptical wheels are so arranged as to give the lever a quick motion, and
revolve valve spindle on to which is secured a cylindrical valve fitting
into a suitable casing having openings communicating with the ports of
the cylinder; when the valve is twisted or revolves with the spindle
steam is admitted until the tappets which are made of various lengths
pass over the tappet lever, when the valve closes and admits no more
steam; when the piston has travelled the length of the cylinder the other
tappet presses the tappet lever in the opposite direction and opens tho
exhaust the full width of the ports quickly, thus giving the steam free
access into the condenser or atmosphere, as the case may be, and greatly
reduce the back pressure on the piston of high-pressure engines.