IMPROVEMENTS IN THE SLIDE VALVES OF STEAM AND OTHER MOTIVE-POWER ENGINES, AND IN APPARATUS CONNECTED THERE WITH
Year: 1870

page_text: PROVISIONAL SPECIFICATION left by James Marshall and William
Bishop Harding at the Office of the Commissioners of Patents, with
their Petition, on the 22nd December 1870.
We, JAMES MARSHALL and WILLIAM BISHOP HARDING, both of
Gainsborough, in the County of Lincoln, Engineers, do hereby declare
the nature of the said Invention for "IMPROVEMENTS IN THE SLIDE VALVES
OF STEAM AND OTHER MOTIVE-POWER ENGINES, AND IN APPARATUS CONNECTED
THERE WITH," to be as follows:-
This Invention has for its object improved arrangements of the slide
valves and apparatus connected therewith for varying the admission of
steam to the cylinders of steam or other motive-power engines. For
this purpose the main slide valve is provided with two or more openings
or ports, through which the induction steam must pass on its way to
the cylinder. The passage of the steam through the ports in the main
valve is controlled by two supplementary or expansion valves placed
at the back of the main valve, such supplementary valves being so
arranged that whilst they have a constant reciprocating motion com-
municated to them, either through the medium of the main valve or
by other suitable mechanism they are at all times at liberty to be

page_text: adjusted by any variation of the governor, so as to advance or retire
over the induction ports in the main valve. This adjustment is effected
by cranks or lever arms keyed on to a spindle controlled by the governor
and mechanism connected therewith, the cranks or lever arms acting
upon inclined surfaces formed at the back of the supplementary or
expansion valves to adjust their position over the induction ports of the
main valve in order to regulate the supply of steam to the cylinder as
the speed of the engine varies. Inclined surfaces may be substituted
for the cranks or lever arms, and arranged to act on the back of the
supplementary or expansion valves to adjust their position as previously
described, or the required adjustment may be obtained by means of right
and left hand screws.
We are thus enabled to dispense entirely with the necessity for using
the ordinary throttle valve, the wiredrawing action of which causes a
considerable loss of the useful effect of the steam. Whilst a constant and
positive reciprocating motion is given to the expansion valves (through
the medium of the main valve or otherwise), they are throughout the
whole stroke of the engine at liberty to be adjusted by the governor in
relation to the induction ports in the main valve, a slight increase or
decrease in the speed of the governor is sufficient to vary the admission
of steam from so small a quantity as shall be just sufficient to drive the
engine alone to admitting the steam up to the point where it is cut off
by the lap on the main valve. The lead and release points are in no
way affected by the variation in the point of cut-off. Any variation
in the point of cut-off is made equal for both ends of the cylinder.
According to our Invention the governor can be caused to act on
two sets of valves simultaneously, so that our improvements are equally
applicable either to single or double cylinder engines.