CERTAIN IMPROVEMENTS IN STEAM ENGINES
Year: 1853

page_text: PROVISIONAL SPECIFICATION left by George Holcroft and William
Jennings Hoyle at the Office of the Commissioners of Patents,
eorge постот
Jennings Hoyle at the Office of the Commissioners of Patents,
with their Petition, on the 2nd April 1853.
(Void by reason of notice to proceed not having been given within the
time prescribed by the Act.)
We, GEORGE HOLCROFT and WILLIAM JENNINGS HOYLE, both of
Manchester, in the County of Lancaster, Engineers, do hereby declare
the nature of the said Invention for "CERTAIN IMPROVEMENTS IN STEAM
ENGINES" to be as follows; that is to say-It relates, firstly, to engines
of that class commonly called trunk engines, and consists in a new
and improved mode of working the steam in them expansively. This
we effect simply by first admitting the steam to one side of the piston
during one stroke, or a part of one stroke, and then expanding the same
steam to the other side of the piston during the next stroke. For this
purpose we construct the trunk which passes through the cylinder cover
to terminate with the piston, so that the area of the piston is much
greater on one side than on the other; and we admit the steam in the
first instance to that side which has the least area, expanding it again
to the other and larger side for subsequent condensation. As the pres-
sures exerted during one entire revolution of the crank will by this

page_text: arrangement be necessarily unequal, wc effect an equalization of the
power by employing two cylinders, and we determine the relative posi-
tion of the two cranks in accordance with this view.
Our Invention has reference, secondly, both to engines of the above
construction and also to those engines which work expansively, by
having compound cylinders, commonly known as Wolff's Engines. It
consists in cutting off the expanding steam before the stroke due to it
is finished. In the trunk engine before described we carry out this
object by constructing the valve or valves so that the passage to the
expanding side will always be closed up at the point desired before the
termination of the stroke; while in double cylinder engines we either
place one or more cut-off valves between the two cylinders, or we give
such an amount of cover to the slide valve of the low-pressure cylinder
as will ensure the cut-off required. It will be perceived by this: arrange-
ment that the steam will undergo an extra amount of expansion, but at
the same time the necessity will be incurred of the steam in the high-
pressure cylinder, or on the high-pressure side of the piston, being
compressed in the steam chest and passages during a portion of the
stroke. If we wish to avoid any inconvenient degree of compression
we cut off this steam also at any point which may be desirable, so that
its elasticity may be diminished previous to the compression taking place.
By making use of this mode of treating steam in expansive engines of
the kind described, some economy will be found to result; but in double
cylinder engines another object is also attained by it which will be
readily seen by practical men, namely, that it enables us to work the
two cranks at any angle to each other.
Our Invention consists, thirdly, in an improved construction of double
heat valve, applicable to the admission of steam in the engines above
described, but which may also be employed with advantage in all
engines where double heat valves are used. In the ordinary valves of
this kind the admission of steam takes place so rapidly as to produce a
vibration on the engine. Our improvement consists in so constructing
the valve as to allow the steam to pass through slowly at first, and after-
wards quicker. This we effect by making a cylindrical projection pass t
the

page_text: face or seat of the valve during the first part of the lift, which projection
may be either vandyked or pierced with holes of any shape, so as to
give the desired effect; or, instead of cylindrical, it may be made conical,
in which case no piercing will be required. The projection may be
either attached to the seating or to the valve itself.