Improvements in Steam Engines.
Year: 1887

page_text: Date of Application, 29th July, 1887.
Specification Accepted, 13th Sept., 1887.
Improvements in Steam Engines.
1 JAMES YATE JOHNSON of 47 Lincoln's Inn Fields in. the County of Middlesex
Gentleman do hereby declare the nature of this Invention which has been com-
municated to me from abroad by Augustin Normand et Cie. of 67 rue du Perrey
Havre in the Republic of France Engineers and in what manner the same is to be
performed to be particularly described and ascertained in and by the following
statement:
The compression of the Steam at the end of the stroke of the piston presents the
advantages, as is well known, of neutralising entirely or partially the prejudicial
influence of clearance and of heating the surfaces of the cylinder which come in
contact with the entering steam and also of enabling the Engine to run at high speeds
which would otherwise be dangerous.
When the exhaust and admission of Steam are controlled by a single valve it
appears impossible, with the arrangements ordinarily employed, to vary the expansion
without producing corresponding changes in the compression. Consequently the
compression cannot be regulated properly for all conditions of expansion.
When the Stephenson link motion, or other analogous arrangements are employed,
the degree of compression increases rapidly with the ratio of expansion, and even
when a special or separate slide valve is employed for the exhaust, there is always a
risk of the slide being slightly out of order and when this occurs the compression
may become excessive so that the pressure of the steam in the cylinders is liable to
rise much higher than that in the valve chest. This is especially the case with the
high pressures now used, where a few degrees of superheating will prevent steam from
condensing without a large increase of pressure.
In order to provide against this danger and obtain from compression all the
advantages that it presents in theory, and render it independent of the ratio of
expansion, the cylinders of steam engines constructed according to this Invention are
provided with safety valves so arranged as to blow off into the valve chest instead of
into the open air. This renders it impossible for the pressure within the cylinder ever
to greatly exceed that in the valve chest and the steam being blown off into the valve

page_text: chest is not wasted. The loss of power resulting from this arrangement is little or
none, as the opening of exhaust is delayed, and in any case the portion of the curve
of the indicator lost by the compression when the Engine is working with great
expansion, corresponds with the end of the stroke where the useful effect produced
upon the crank shaft is almost nil.
The safety valves are pressed to their seats by the pressure existing within the slide
valve chest so that an extremely slight spring is sufficient to ensure perfect contact
with the seats, and a prompt closure directly the excess of pressure which has opened
or lifted, the valve is removed. Moreover the period of time available for closing the
valve is always sufficient even when the Engine is running at a high speed, as it is
equal to that comprised between the admission and the cut off of steam.
Valves which are almost noiseless in their action are now employed in air pumps,
and it is evident that the same or analogous arrangements may be employed in the
present case with like results. Moreover there is not the same tendency to produce a
loud noise as there is with ordinary valves which require to be heavily loaded. By
making the joint of the valve with lead or other but slightly elastic substance a
noiseless action can be ensured.
Slide valves arranged to lift slightly in case of an excess of pressure in the interior
of the cylinder could not be employed with the same effect, as the rubbing surfaces
would wear out rapidly, and the noise produced would be objectionable. These new
valves enable the ordinary safety or blow off valves of the cylinders to be dispensed
with. They suffice to let off any water that may accumulate in the cylinders a single
blow off cock being placed on the valve chest.
Figure 1 of the accompanying drawings represents a section of a part of a steam
engine constructed according to this Invention the section being taken along the
line IJ figure 2. Figure 2 is a section taken along the line KL figure 3 and
Figure 3 is a section taken along the line M N figure 2. Figure 4 represents one of
the blow off valves in a section taken along the line OP figure 3. In this engine
which is merely given as an example to show how the Invention may be carried out
in practice the steam cylinder is represented at A the supply passages at B and the
exhaust at C. The valves which allow the excess steam compressed by the piston at
the end of the stroke to escape into the valve chest are indicated in section at D in
figures 1 and 4 and are seen in dotted lines in figures 2 and 3.
These valves communicate on the one hand with the interior of the cylinder through
passages EE (Figures 1 and 2) and open directly into the steam chest on the other
hand as indicated in the drawing.
Having now particularly described and ascertained the nature of the said Invention
and in what manner the same is to be performed I declare that what I claim is :-
First. A steam engine having safety or blow off valves at each end of the cylinder
or cylinders the said valves being arranged to blow off into the valve chest for the
purpose of enabling a suitable amount of compression to take place at the end of the
stroke with any desired degree of expansion and rendering it impossible for excessive
pressure to be created by the compression substantially as hereinbefore described.
Second. The general arrangements and combinations of parts constituting the
improved steam engine substantially as hereinbefore described with reference to the
accompanying drawings.
3011
T
1007
J. H. JOHNSON & Co.,
47, Lincoln's Inn Fields, London, W.C.,
Agents.