Year: 1886

page_text: Date of Application, 8th Oct., 1886.
Complete Left, 8th July, 1887.
Complete Accepted, 6th Sept., 1887.
WM. P. THOMPSON & Co.,
Of 6, Lord Street, Liverpool,
Patent Agents for the Applicant.

page_text: I, THOMAS MUDD of Hartlepool in the County of Durham, Engineer, do hereby
declare the nature of this invention and in what manner the same is to be performed,
to be particularly described and ascertained in and by the following statement :-
The object of my invention is to construct a piston which shall be cheaper, more
durable, and more efficient in its working than those generally in use at the present
time.
I accomplish the object of my invention mainly, by a particular construction and
arrangement of the piston springs and rings. These parts are so constructed and
arranged, that while not diminishing, but rather increasing, the efficiency of the
piston, they at the same time are small in first cost, very durable, and capable of being
easily and expeditiously repaired and adjusted.
The attribute of cheapness in first cost I obtain by constructing the parts of a
simple form, which admits of them being made in quantity, and by making them as
far as possible interchangeable.
I obtain great durability in the rings by so arranging the springs that the pressure
between the former and the cylinder shall be equal or nearly equal at all points, and
by not allowing this pressure to be much greater than what is necessary to keep the
piston steam tight.
By making the springs of a simple form and interchangeable, they may be readily
and with very little skill adjusted or re-tempered.
The way in which I prefer to carry out my invention may be best described by
reference to the accompanying drawings in which,
Figure 1 is a plan of my improved piston with the junk ring removed.
Figures 2 and 3 are sections on lines x, x, and y, y, (Figure 1) respectively.
Figures 4, 4, and 5 show slight modifications of the foregoing.
In these A is the body of the piston, B is the junk ring. The packing consists of
an upper and a lower packing ring C and C¹ each being of plain rectangular section,
capable of being cheaply made by casting a lot together in the form of a cylinder,
and cutting them off in the lathe.
These rings are very strong and stout, and present a wide bearing surface to the
piston flange A and junk ring B. They are split transversely as usual and may be
made either with or without a tongue piece.
At intervals around the rings (, C, (varying in amount to suit the pressure of
steam uuder which the rings are to work) I make holes in the upper surface of the
lower ring, and in the under surface of the upper ring, and into these I insert vertical
springs D of a simple helical form, which are easily and cheaply made and can be
readily tempered.
When the junk ring B is screwed down, these vertical springs are compressed, and
a powerful pressure is exerted by them quite centrally to the section of the rings,
holding the rings with such force against the piston flange A¹ and junk ring B that
the steam pressure, which I hold must inevitably find its way into the ring recess, and

page_text: behind the packing rings, is powerless to press the rings unduly against the wall of
the cylinder, on account of the high frictional resistance set up between the lower
and upper faces of the rings against the piston flange and junk ring.
Between the holes for the vertical springs D, I make similar holes on the inner
periphery of the rings, so that radial springs D', quite similar in character, and
preferably in size, may be inserted in them and press against the piston body A, or
a separate solid floating ring, or any well known principle. In an ordinary split
piston ring, the pressure on the cylinder is greatest at the joint, and least at a point
diagonally opposite to this. The radial springs D¹ however, (which are preferably
interchangeable with the vertical springs D) are arranged so as to produce equal or
nearly equal pressure on all portions of the rings C and C₁, and they are prevented
from exerting undue pressure on the cylinder by the frictional resistance between the
rings and the junk ring or piston flange.
I taper the upper edge of the piston body or floating ring as at d to facilitate the
insertion of the ring in its place when all the radial springs are in position. The
section of the rings is sufficiently large to allow of a similar helical spring D* being
also inserted tangentially at the joint of each of the rings, if desirable.
It will thus be seen that all the pressures requisite, (namely longitudinally to the
cylinder, radially to the piston, and tangentially to the rings) are secured by one
universal form of spring, and that form a simple short helical coil of round or other
shaped steel wire, which it is within the power and capacity of every engineer in
charge of the machinery to temper and re-temper or otherwise adjust, as occasion
arises.
This universality of form for all positions, and for all pistons, is of the very highest
importance.
Also the section of the rings being a plain rectangle and uniform, their enlargement
in following up wear has no tendency to buckle them or prevent them sitting truly
and fairly on the piston flange and junk ring, and they are from the same cause
capable of much greater range of enlargement than rings of irregular section.
And further a steam-tight and most efficient piston packing is formed with the
minimum of friction against the walls of the cylinder, and at an exceedingly low cost,
the latter on account of the easy manufacture of the rings in the lathe, as above
described, and the simplicity and universality of form of the springs enabling them
to be made with great rapidity.
Though the best results may be obtained by using the radial springs I do not regard
them as an essential part of the invention as in some cases they may be found
unnecessary.
I am aware that helical springs placed radially as herein described have been
previously used in pistons. I do not therefore claim their use except as combined
with other parts of my invention.
In pistons of large diameter where two rings are used bearing against the cylinder
a bad effect is apt to arise from instability of the rings causing ridging at top and
bottom of the cylinder. The longitudinal spring forces being applied in the centre of
the breadth of the rings tends greatly to increase the stability; but to obviate all
trouble from this cause in pistons of large diameter and working at low steam pressure
I insert a plain ring outside the two rings described and between them and the
cylinder. This arrangement is shown in one form at figures 4 and 4° and another
form is shown in Figure 5 with the plain ring C2 next the cylinder and behind this
two rings and held to its face by their own elasticity or by radial springs D¹
either coiled or otherwise and forced apart longitudinally to the cylinder by a series
of vertical coiled or other springs D (around pins or otherwise). The radial springs
can be similar to the vertical ones as in the piston previously described, and can
either bear against the piston body or against a floating ring as preferred.
The method of inserting an outer wearing ring may be applied with advantage to
any of the existing forms of modern piston packings where two rings are used such
as Buckleys, Rowans, Maclaine's, Oldham's Mather & Platt's, Carlisle's, The
Lancaster &c.

page_text: 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 :-
1. In a piston, the combination of packing rings C of rectangular cross section
with helical springs D located between said packing rings and tending to force them
against their respective bearing surfaces on the junk ring and piston flange and with
similar helical springs D¹ placed radially to the said packing rings, and so arranged
as to cause the said rings to bear with equal or nearly equal pressure throughout
their contact with the cylinder, substantially as and for the purpose described.
2. In a piston, the combination with the packing rings C and C of a series of
helical springs enclosed between said rings, and forcing the same against their
respective bearing surfaces on the junk-ring and piston flange, whereby such a
frictional resistance is created between the said complementary bearing surfaces, as to
prevent any undue lateral pressure between the said packing rings and the cylinder,
substantially as and for the purpose shown and described.
3. In a piston, the use of a series of similar and interchangeable short helical
springs, whereby all the requisite pressures, namely, longitudinally to the cylinder,
radially to the piston, and tangentially to the rings, are secured by one universal form
of spring, said spring being simple to manufacture, and easy of adjustment.
4. In a piston having two or more packing rings pressed upon radially and
longitudinally to the cylinder in the manner herein described, a plain cut ring
placed outside said packing rings against the cylinder, said plain ring surrounding
the aforesaid packing rings, and extending the whole width between the junk-ring
and piston flange, substantially as and for the purpose set forth.
WM. P. THOMPSON & Co.,
⚫ Of 6, Lord Street, Liverpool,
Agents for the Applicant.