IMPROVEMENTS IN THE CONSTRUCTION OF SLIDE VALVES FOR STEAM ENGINES
Year: 1876

page_text: LETTERS PATENT to Henry Bamford, of Pentonville, in the County of Mid-
dlesex, Engineer and Machinist, for the Invention of "IMPROVEMENTS IN THE
CONSTRUCTION OF SLIDE VALVES FOR STEAM ENGINES."
Sealed the 15th June 1877, and dated the 18th December 187
PROVISIONAL SPECIFICATION left by the said Henry Bamford at the Office
of the Commissioners of Patents on the 18th December 1876.
HENRY BAMFORD, of Pentonville, in the County of Middlesex, Engineer and
Machinist. "IMPROVEMENTS IN THE CONSTRUCTION OF SLIDE VALVES FOR STEAM
ENGINES."
My Invention has for its object the construction of the main slide or slides of a
steam engine in such a manner as to insure that, at whatever part of the stroke
steam is cut off, the exhaust port of that side of the piston shall remain closed, and
the exhaust port of the other side remain open till the end of the stroke, thereby
giving the full benefit of expansion and removing the disadvantage of compression,
which objects cannot be obtained in the ordinary slide. By this arrangement the
outside lap is alternately changed from end to end of the slide, being always on
the advancing or cut-off side, thereby allowing the steam in the cylinder to expand
until the steam port is opened at the opposite end, the exhaust port opening at the
same time. For this purpose the main slide valve of a steam engine is made to
consist of two principal parts, which may be called the inner and outer slides, and
which are caused to act in combination in the manner herein-after stated. These
two slides, or two parts of the slide valve, both fit and move on the same face,
which may be of the ordinary three-ported description, or may have any required
number of steam and exhaust ports in order to give increased area for the admission
and exit of the steam.
In the case of a three-ported slide face, the inner slide, or inner part of the com-
pound slide valve, will exactly correspond in its exterior or exhaust passage with
the inside of an ordinary D slide valve, the length of the opening being equal to
the width of the exhaust port and the two bars of the slide face together, or there-
abouts. The two outside end of this slide will when in a central position half
cover each steam port, or thereabouts. The outer slide surrounds the inner slide

page_text: like a rectangular frame, and corresponds in its outside edges with the outside of
an ordinary D slide valve with the required amount of outside lap. It fits closely
to the inner slide on the two sides parallel to the line of its motion; its inside
length in the direction of motion exceeds the outside length of the inner slide by
a distance equal to the amount of lap required. The thickness of its ends is equal
to half the width of the steam port, or thereabouts.
The two slides, or two parts of the compound slide valve, will be covered by a
plate or other suitable means for preventing the steam from entering between them,
and so arranged as to regulate the pressure of the steam on thein in such a manner
as to insure that the inuer slide will remain stationary on the face till the outer
slide has travelled the distance of the lap, when the inner slide will be moved
through the remainder of the stroke by the abutment of the outer slide against
its end, this action being reversed in the return stroke, and so on alternately.
The outer slide is connected to the slide rod, and driven by an eccentric or other
means in the ordinary manner.
The cut-off may be varied by altering the stroke of the outer slide, or by making
the outer slide in two parts adjustable by right and left handed screws, so as to
alter the outside lap, or by a combination of both.
The Invention is also applicable to long slides, when the two ordinary slides
would be replaced by slides constructed as above described.
SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Henry Bamford in the Great Seal Patent Office on the 16th June
1877.
HENRY BAMFORD, of Pentonville, in the County of Middlesex, Engineer and
Machinist. "IMPROVEMENTS IN THE CONSTRUCTION OF SLIDE VALVES FOR STEAM
ENGINES."
My Invention of "Improvements in the Construction of Slide Valves for Steam
Engines" has for its object the construction of the main slide or slides of a steam
engine in such a manner as to insure that at whatever part of the stroke the steam
is cut off the exhaust port of that side of the piston shall remain closed, and the
exhaust port of the other side remain open till the end of the stroke, thereby giving
the full benefit of expansion and removing the disadvantage of compression, which
objects cannot be attained in the ordinary D slide. By this arrangement the
outside lap is alternately changed from end to end of the slide, being always on
the advancing or cut-off side, thereby allowing the steam in the cylinder to expand
until the steam port is opened at the opposite end, the exhaust port opening at or
near the same time. For this purpose the main slide valve of a steam engine is made
to consist of two principal parts, which may be called the inner and outer slides,
and which are caused to act in combination in the manner herein-after stated.
These two slides or two parts of the slide valve both fit and move on the same
face, which may be of the ordinary three-ported description, or may have any
required number of steam and exhaust ports, in order to give increased area for the
admission and exit of the steam.
In the case of a three-ported slide face the inner slide, or inner part of the com-
pound slide valve, will exactly correspond in its interior or exhaust passage with
the inside of an ordinary D slide valve, the length of the opening being equal to
the width of the exhaust port and the two bars of the slide face together, or there-
abouts. The two outside ends of this slide will when in a central position half
cover each steam port, or thereabouts. The outer slide surrounds the inner slide
like a rectangular frame, and corresponds in its outside edges with the outside of
an ordinary Ď slide valve with the required amount of outside lap. It fits closely
to the inner slide on the two sides parallel to the line of its motion; its inside

page_text: Fig. 1 is a longitudinal section through the slide and passages of a steam cylinder
with an ordinary three-ported face; Fig. 2 is a half plan of the same; Fig. 3 is a
longitudinal section of a slide working on a face with three ports at each end, and
one exhaust port in the centre; and Fig. 4 is a half horizontal section of the same
on the line Y, Z, of Fig. 3.
In these several Figures the same letters of reference indicate corresponding
parts.
A is the cylinder face, B, B, are the steam ports, C, the exhaust port. D is the
inner slide or inner part of the slide valve, and E the outer part of the same,
which two parts are made to fit and move on the face A as required; F is the rod
for working the valve, which rod is connected to the outer part E of the valve.
In Fig. 1 the part D regulates the exit of the steam from the cylinder only.
It corresponds.in its interior or exhaust cavity with an ordinary slide, the distance
from a to b being equal to the width of the exhaust port C and the two bars of the
slide face A. It also carries on its back the plate G, which for convenience of fitting
may be made separate, and fastened to it by screws or other means. The under
face of this plate is faced perfectly true, and is paralled to the slide face on the
cylinder.
The part E regulates the admission and cut-off of the steam only, and is con-
nected to the rod F by any of the means now in use; it fits sufficiently close to the
part D on the two sides parallel to its line of motion to keep this part D always
parallel with it, but at the same time is sufficiently loose to allow of its travelling
the distance c, d, independently of the part D. The thickness of the ends of the
part E is such that when it abuts against the part D the width of the two together
(from e to f) will exceed the width of the steam port as much as may be desired.
The steam is prevented from entering between the two parts D and E by the ring H,
which is kept tight against the plate G by the pressure of the steam between it and
the part E, which is also kept tight on the slide face A by the pressure of the steam.
This arrangement with a ring may however be varied if preferred. The total
pressure on the back of the two parts D and E can be divided between them, so as
to make them wear equally on the cylinder face by properly proportioning the area
exposed to steam pressure on each of such parts, the inside area of the ring H

page_text: (when such ring is employed) regulating the pressure on the part D, and the area
beyond it regulating the pressure on the part E.
The action of the slide is as follows:-Supposing the slide to be at the end of
its stroke, the steam would be entering the cylinder port at B¹, the other port
being open to the exhaust passage, a distance as much in excess of the steam opening
as the distance from e to f exceeds the width of the steam port. On the return of
the excentric the part E would be carried with it, and be caused to cut off the steam,
the part D remaining stationary. The part E alone would continue to move until
it had travelled the distance d, c, when it would abut against the part D, and carry
it with it for the remainder of the stroke; the parts D and E would then be in the
reverse position to that shown in the Drawing. The excess of the distance from e
to over the width of the steam port would cause the exhaust passage to close
Blightly before the end of the stroke, thereby forming a steam cushion at each end
of the cylinder.
It is necessary that there should be a communication between the two ends of
the space between the two parts D and E, in order that there may be no com-
pression of the steam that may be between them.
The part D can be relieved of part of the steam pressure on its back by a ring
or other means commonly used, in which case the ring G would be made of larger
internal area, in order to reduce the pressure on the part E.
In the form of slide valve, represented at Figures 3 and 4, the part D is made
with two bars across its inner or exhaust cavity, so as to open and close two ports
nt each end simultaneously. The action of this slide valve is exactly similar to
the three-ported slide, the part E being connected to the rod (not shown), and
travelling the distance c, d, independently of the part D, which is then taken with
it for the remainder of the stroke.
The two end ports are used for the admission of steam only; the centre ports
at each end are used for both admission and exit of steam, and the two inner ports
at each end are used for the exit of the steam only, thereby making always two
ports open for the admission and two for the exit of the steam, as indicated by the
arrowa in Fig. 3. A ring of the ordinary description can be fitted to the back of
the slide to relieve it of some of the pressure.
The Invention, as above described, is applicable also to engines worked by com-
pressed air, gas, or other elastic vapour.
Having thus described the nature of the said Invention, and in what manner the
same is to be performed, I hereby declare that what I claim as of my Invention is,
the construction of slide valves in two parts kept on the slide face by the pressure
of the steam, as above described, for the purpose of reversing the whole or part of
the lap alternately from end to end of the slide, as herein-before described.
In witness whereof, I, the said Henry Bamford, have hereunto set my
hand and seal, the Sixteenth day of June, in the year of our Lord One
thousand eight hundred and seventy-seven.
Witness,
WILLIAM SPENCE,
8, Quality Court,
Chancery Lane.
HENRY BAMFORD. (L.S.)