IMPROVEMENTS IN DIRECT-ACTING STEAM PUMPING ENGINES
Year: 1875

page_text: PROVISIONAL SPECIFICATION left by Henry Cherry at the Office of
the Commissioners of Patents, with his Petition, on the 10th
August 1875.
I, HENRY CHERRY, of Aston, near Birmingham, in the County of
Warwick, Mechanical Engineer, do hereby declare the nature of the said
Invention for "IMPROVEMENTS IN DIRECT-ACTING STEAM PUMPING ENGINES," to
be as follows:-
I construct the main valve or valves and port faces which control the
admission and emission of steam from the cylinder with such a con-
figuration of the edges controlling the admission and emission of the
steam, that a reduction in the length of stroke of the valve or valves
will reduce the area available for the admission of steam without
affecting that for the emission to a prejudicial extent.
I construct the subsidiary valve or valves which control the admission
and emission of steam to the piston or pistons, which move the main
valve or valves controlling the admission of steam to the cylinder, and the.
gear for moving the said subsidiary valve or valves in such a manner that.

page_text: while the main piston travels its normal stroke the main valve travels
its full stroke, but if the main piston travels beyond its normal distance
the travel of the main valve is reduced, and the area available for the
admission of steam is reduced also.
I construct the steam cylinder double, that is, with a smaller cylinder
within it, which smaller cylinder has a casing surrounding it forming a
steam jacket. There are two pistons one annular with packings working.
steam tight in the bore of the large cylinder and outside the casing of
the smaller cylinder. The other piston works in the smaller cylinder.
The main valve or valves while admitting steam to the front end of
the smaller cylinder allow the steam from the back end to exhaust into
the front annular space of the larger cylinder, and on the pistons
making their stroke the steam is expanded to whatever extent the
annular area exceeds that of the smaller piston. Similarly for the
return stroke the steam is admitted to the back end of the smaller
cylinder, and the steam from the front end exhausts into the back
annular space. The steam from the annular space may exhaust into the
atmosphere or into a condenser or otherwise.
I carry out these improvements in the following manner:-On the
steam cylinder I bolt the steam chest containing the main slide valve in
the usual way. The steam chest is bored out at each end to receive the
pistons which move the main valve. I cast these pistons in one piece
and place the subsidiary valve that admits steam to them on the
connecting part of the casting. The subsidiary valve is held between
fixed guides so that it cannot move with the said pistons, but can move
at right angles to their motion, and is moved by tappets or levers by the
main pistons. The ports and passages for the admission and exhaustion
of steam from the said pistons are formed in their casting, and I shape
the edges and exhaust cavity of the said subsidiary valves in such a
manner that in normal working the steam is cut off, and the exhaust
opened to the said pistons at such points in the stroke that the main
valve shall travel its normal stroke; but if the main piston travel
beyond its normal distance then the subsidiary valve will receive a
longer travel, and its edges, and exhaust cavity will be so disposed
that the steam will be cut off earlier, and the exhaust opened earlier
to the pistons which move the main slide valve, thus shortening its
stroke.

page_text: It will be understood that the motion of the subsidiary valve across
the said pistons opens the steam and exhaust ports to the said pistons,
while the motion of the said pistons beneath the subsidiary valve cuts off
the steam from the piston taking steam and opens the exhaust to it.