Year: 1888

page_text: 1, BIAGIO BIANCHETTI, of Geneva, Switzerland, 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 :-
My invention has for its object to prevent the excessive outward pressure to which
the packing rings of steam engine pistons are subject by the steam which penetrates
into the groove of the piston, more particularly in engines working at very high
pressures, such as the double, triple, or quadruple expansion engines now largely
employed.
During the stroke of a piston, the steam acting on one side thereof penetrates into
the annular chamber formed between the bottom of the piston's groove and the inner
surface of the packing rings, which steam, after a certain number of strokes of the
piston, will acquire the full pressure and in pressing the packing rings outwards with
a corresponding considerable force, in addition to that due to the spring action of the
packing rings, causes excessive frictional resistance, resulting in a considerable loss of
power, and also, causing great wear and tear.
This pressure is practically maintained during the whole of each stroke of the
piston, as when the steam on the working side of the piston expands and then exhausts,
the steam in the said annular chamber cannot become reduced in pressure in a
corresponding manner, as it has no outlet beyond the very small crevices through
which it enters, and it would take as long to leak out through these as it did to enter
on starting the engine.
According to my present invention I obviate the above defect by providing in the
piston special passages which are automatically opened and closed at the required
moments for allowing the escape of steam pressure from such annular chamber on the
exhaust side of the piston, and at the same time for preventing the steam from
entering the chamber through such passages on the return stroke.
On the accompanying drawing is shewn by way of example an arrangement for
carrying out my said invention by means of two valves C and D which are in
communication with each other through the annular chamber E behind the packing
ring F.

page_text: The valve C puts the annular chamber in communication with the exhaust side of
the piston through the holes G when the steam is acting on the underside of the
piston while it prevents the steam from entering the chamber when it is acting on the
upperside. The valve D on the other hand puts the chamber in communication with
the exhaust side through the passage H when steam is acting on the upper side of the
piston and prevents the steam from entering when it acts on the underside.
Thus it will be seen that the pressure of the steam in the chamber E will practically
never exceed that of the exhaust, not taking into consideration the small weight of
the valves themselves.
Fig. 1 of the drawings shews a plan, Fig. 2 a section on line X X and Fig. 3 a
section on line Y Y.
The invention is applicable with particular advantage to high pressure engines, to
the high pressure cylinders of compound engines, to the high pressure and medium
pressure cylinders of triple expansion engines, and to the high pressure and two
medium pressure cylinders of quadruple expansion engines.
By the use of the invention a considerable saving will be effected both in fuel and
in wear and tear in all steam engines.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, I declare that -what
I claim is :-
1. In steam engine pistons, the provision of means whereby the space behind the
packing rings is automatically put in communication with the exhaust side and is
closed against the steam side, so as to prevent the accumulation of detrimental steam
pressure behind the packing, substantially as herein described.
2. The employment in a steam engine piston of two valves, such as C and D,
operating in combination with the space E behind the packing and with passages G
and H communicating respectively with opposite sides of the piston, substantially as
and for the purposes herein described.
Dated this 21st day of Inns 1000