IMPROVEMENTS IN AND RELATING TO STEAM ADMISSION AND EXHAUST VALVES, KNOWN AS PISTON VALVES
Year: 1884

page_text: I JOHN THOM of 39, Harrison Street, Barrow-in-Furness in the County of
Lancaster, Engineer do hereby declare the nature of the said Invention for
IMPROVEMENTS IN AND RELATING TO STEAM ADMISSION AND EXHAUST VALVES,
KNOWN AS PISTON VALVES to be as follows:
My Invention relates to a novel construction of what are known as piston valves
for steam engines. The construction of the valve being such that a communication
is formed between the ends of the cylinder through a passage, similar to the passage
employed in what is known as a Trick valve, and whereby a portion of the
steam from one side of the piston at terminal pressure is transferred from one end
of the cylinder to the other, and used over again on the return stroke.
«
My Invention consists in providing the working face of the piston valve with
a passage similar to the passage in a "Trick" valve, but having positive and,
negative exhaust lap at top and bottom of the cylinder, so that the negative
exhaust lap forms a communication between the opposite ends of the cylinder, just
before exhausting to the condenser and so that steam at its terminal pressure is
transferred from one side of the cylinder piston to the other through the passage,
such steam being then compressed nearly up to the initial pressure and used over
again on the return stroke of the engine. The exhaust may be single, or double.
If the exhaust is made double, this is done by forming a ring round the exhaust
Bide of the piston valve and making a double port in the cylinder valve face. This
arrangement greatly reduces the travel of the valves, and provides a better cut off
and steam admission than is obtained with the ordinary single ported piston valve.
The valve face of the piston valve is kept tight by packing rings and springs or
other known method, or it may be made a good working fit without springs.
The piston valve may be arranged so that the steam enters from the outside ends
of the piston valve and the exhaust takes place at the centre, or the steam may
enter at the centre and the exhaust take place at the ends of the valve, if more
convenient.
By the use of my improved piston valve, steam is taken through the passage in
the valve from one end of the cylinder after performing its usual work, and
compressed at the other end of the cylinder nearly up to the initial pressure, using
the work stored in the piston and other moving parts for this purpose, and causing
the engines at the same time to turn the centres especially the low pressure cylinder
of compound engines with less shock, due to having stean in the cylinder to
compress.
DIL
T

page_text: I JOHN THOM of 39 Harrison Street, Barrow-in-Furness in the County of
Lancaster, Engineer do hereby declare the nature of the said Invention for
IMPROVEMENTS IN AND RELATING TO STEAM ADMISSION AND EXHAUST VALVES,
KNOWN AS PISTON VALVES and in what manner the same is to be performed, to be
particularly described and ascertained in and by the following statement:-
My Invention relates to a novel construction of what are known as piston valves.
for steam engines. The construction of the valve being such that a communication
is formed between the ends of the cylinder through a passage similar to the passage
employed in what is known as a "Trick" valve and whereby a portion of the
steam from one side of the piston at terminal pressure is transferred from one end
of the cylinder to the other, and used over again on the return stroke.
My Invention consists in providing the working face of the piston valve with
a passage similar to the passage in a "Trick" valve, but having positive and
negative exhaust lap at top and bottom of the cylinder,, so that the negative
exhaust lap forms a communication between the opposite ends of the cylinder just
before exhausting to the condenser and so that steam at its terminal pressure is
transferred from one side of the cylinder piston to the other through the passage,
such steam being then compressed nearly up to the initial pressure and used over
again on the return stroke of the engine. The exhaust may be single, or double.
If the exhaust is made double, this is done by forming a ring round the exhaust
side of the piston valve and making a double port in the cylinder valve face. This
arrangement greatly reduces the travel of the valves and provides a better cut off
and steam admission than is obtained with the ordinary single ported piston valve.
The valve face of the piston valve is kept tight by packing rings and springs, or
-other known method, or it may be made a good working fit without springs.
The piston valve may be arranged so that the steam enters from the outside ends
of the piston valve and the exhaust takes place at the centre, or the steam may
enter at the centre and the exhaust take place at the ends of the valve if more
convenient.
The above being a general description of my Invention, that the same may be
more clearly understood, I will now proceed to describe with the aid of the
Drawings hereto annexed and which form a part of this Specification, how my
Invention may be carried out into practical effect by others skilled in the art to
which it appertains, like letters and figures in the Drawings being used to dénote
like, or corresponding parts throughout the views.
DESCRIPTION OF THE DRAWINGS.
Figure 1 illustrates a slide. valve and valve face constructed with my improve
ments applied thereto.
Figure 2 is a section through X X Figure 1.

page_text: With reference to the Drawings A is the valve. B is the valve face. C are the
cylinder ports. D is a portion of the piston. a is a passage through the valve,
having ports a¹ a². The passage a is in some respects similar to the passage in
what is known as a "Trick" valve, but the ports a¹ a² of the passage a are so
arranged in reference to the ports in the valve face (hereinafter described) that the
passage a serves to supply steam to the cylinder in a similar manner to a "Trick"
valve and also to form a communication between the opposite ends of the cylinder,
so that a portion of the steam from one side of the piston at terminal pressure is
transferred from one end of the cylinder to the other and used over again on the
return stroke. The annular chamber F round the valve A in Figure 1 forms the
exhaust space. In Figure 3 the annular chamber F forms the exhaust space also,
but in this case the exhaust steam enters the chamber F by the circumferential
passage F¹. bb¹ are the ports in the valve face, the ports b serving for both steam
and exhaust and the ports 6¹ serve for exhaust only. The annular passage b' serves
for the main exhaust for both ends of the cylinder.
In operation the working of the valve will be as follows: Upon reference to
Figure 1 the valve is shown at the point at which communication is opened
between the ends of the cylinder, so that the steam passes through the port a¹
passage a and port a³ to the opposite end of the cylinder. The valve travelling
along in the direction of the arrow closes the port a² and compression of the steam,
which has passed from one end of the cylinder to the other takes place. Soon after
the passage a is closed the exhaust is opened to the opposite side of the piston.
When the piston has arrived at the end of the stroke steam is admitted from the
outside of the valve and also through the "Trick" passage a and the return stroke
is made.
The valve face of the piston valve is kept tight by packing rings c kept up with
springs.
By the use of my improved piston valve steam is taken through the passage in
the valve from one end of the cylinder after performing its usual work, and
compressed at the other end of the cylinder, nearly up to the initial pressure using
the work stored in the piston and other moving parts for this purpose and causing
the engines at the same time to turn the centres especially the low pressure
cylinder of compound engines with less shock, due to having steam in the cylinder
to compress.
Having now particularly described and ascertained the nature of my said
Invention and in what manner the same is to be performed I declare that what
I claim is
•
First Constructing and arranging piston valves with a "Trick" valve arrange-
ment so that the inside edges of the ports of the "Trick" passage have a negative
lap thereby effecting a communication between the ends of the cylinder at the end
of the stroke of the piston as set forth and as shown in the Drawings hereto
annexed.
Second Constructing and arranging piston valves with a double exhaust and a
double steam port substantially as set forth.