Improvements in Differential Pressure-reducing Apparatus.
Year: 1894

page_text: Date of Application, 21st Dec., 1894-Accepted, 23rd Feb. 1895
Improvements in Differential Pressure-reducing Apparatus.
I, CARL GUSTAF PATRIK DE LAVAL of 16 Handtverkaregatan, Stockholm,
Sweden, Doctor of Philosophy and 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 :—
This invention refers to differential pressure reducing apparatus that is to say
an apparatus for automatically maintaining a previously determined constant
difference between the pressures of two fluids independent of the variations in
pressure which may obtain in one or both of these fluids. The apparatus is
especially intended for use with steam boilers for high pressure where a water
pressure is desired for regulation which independent of the variations in the steam
pressure keeps somewhat higher or lower than the steam pressure.
On the annexed drawing which is a longitudinal section of the apparatus, a is a
piston which is movable in the cylinder b. This piston is provided with two cross
passages c and d which communicate by the length passage e.
The passage c
connects by the passage in the pipe g with a conduit from the feed pump while
the passaged by means of the passage in the cylinder wail communicates with a
space below the cylinder or forming part thereof. This space has an outlet
pipe for that water the pressure of which is kept at a certain and constant
distance from the steam pressure..
The piston a is with a spindle part continued into this space and is influenced by
the spring fixed at its upper end and the pressure of which on the piston a can
be adjusted by the nuts m. The upper end of the cylinder forms a steam inlet.
The water coming from the pump at a greater pressure than that of the steam
acting upon the other end of the piston a and the pressure of which is desired to
be reduced in the manner stated enters by gfeed h into the space i filling it at
last and flowing out by the pipe k.
But as soon as the water pressure on the piston a rises so high that it together
with the pressure of the spring on the piston overcomes the pressure of the steam
on the other end of the piston, the piston is shifted and the water admission
through e ed is shut off or throttled. The pressure in the space i then goes down
until equilibrium is effected between, on the one hand the steam pressure on the
upper end of the piston and on the other hand the water pressure and that of the
spring on the other end provided that the outflow at k is less than by fully opened
passages ce d.
The degree of pressure in the space i will thus always be at a certain distance
from the steam pressure acting on the upper end of the piston however much the
water or steam pressure may vary. For as soon as the former tends to rise the
piston is pushed upward thereby throttling the inlet until equilibrium is established.
Vice rerra when the water pressure diminishes the piston is pushed down whereby
the inlet is opened. In like manner the piston is pushed up or down if the steam
pressure rises or falls. The pressure in the space i will thus by this arrangement
independently of the pressure variations of the water or the steam be kept so
much lower than the steam pressure on the upper end of the piston as is the
pressure of the spring at the lower end of the piston. As this spring pressure
may be regulated as desired by means of the nuts m the pressure of the water
passing through the apparatus described will be reduced to a pressure which is to
a desired degree lower than the steam pressure that is to say I attain a desired and
constant difference.

page_text: The spring I may of course be arranged on that side of the piston a which is
acted on by the steam but the arrangement shewu is probably preferable. It
should here be noted that as the desired difference between the pressure of the
steam and water in the aforesaid arrangement is obtained by acting on the piston a
with a force which is just as great as this difference this force ought to be constant
in the various positions of the piston in so far as it is desired that the difference
should be constant. It would therefore be more correct to load the piston with a
weight instead of the spring or to make it so heavy that its own weight produces,
the required throttling of the water. But in order to alter easily the desired
difference it may be more suitable to apply a spring which is made so long that
the varying pressure exerted by the spring on the piston in the various positions of
the latter has no material influence.
The pressure of the water flowing off through k may of course in the apparatus
described be kept somewhat higher than the steam pressure by reversing the
pressure action of the spring or weight.
In order to avoid a displacement of the piston a and a jambing of same because
of the pressure action of the in-flowing water in case the throttling device as in
the example shewn consists of the piston itself (which for that purpose is provided
with passages c d communicating with the water inlet g and with the space i) the
inlet passage runs at right angles to the direction of motion of the piston and
terminates symmetrically round the piston that is to say in an annular groove fl
in the cylinder. The piston thus becomes balanced and insensible to the inlet of
the water.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed I declare that what I
claim is :-
1. Apparatus for producing in connection with steam boilers a constant difference
between the steam pressure and a water pressure, independent of the pressure
variations of these fluids, for the purpose of regulating for instance the power
supply to the motor by keeping the water pressure somewhat lower or higher than
the steam pressure consisting of a piston or diaphragm movable in a cylinder and
connected with a throttling device for the water (or itself forming a throttling
device) such device being on one side acted on by the steam pressure and on the
other by the reduced water pressure and by the force practically constant in all
positions of the piston, of a spring or weight, substantially as set forth.
2. In an apparatus of the kind firstly claimed in the case where the piston itself
forms the throttling device, the termination of the water inlet opening symmetrically
round the piston for the purpose of avoiding the shifting or jambing of the piston
by reason of the pressure action of the water substantially as set forth.
Dated this 20th day of December 1894
JENSEN & SON,
77, Chancery Lane, London, W.C., Patent Agents.
JENSEN & SON,
77, Chancery Lane, London, W.C., Patent Agents.