AN IMPROVED METHOD OF AND APPARATUS FOR UTILISING COMPRESSED AIR IN THE MANAGEMENT OF RAILWAYS, IN SIGNALLING TRAINS, ELEVATING WATER, PROTECTING TELEGRAPH WIRES, AND FOR other' PURPOSES
Year: 1874

page_text: LETTERS PATENT to William Edgar Prall, of the City of Washington,
in the District of Columbia, and United States of America, for the
Invention of "AN IMPROVED METHOD OF AND APPARATUS FOR UTILISING
COMPRESSED AIR IN THE MANAGEMENT OF RAILWAYS, IN SIGNALLING
TRAINS, ELEVATING WATER, PROTECTING TELEGRAPH WIRES, AND FOR other'
PURPOSES."
.
PROVISIONAL SPECIFICATION left by the said William Edgar Prall
at the Office of the Commissioners of Patents, with his Petition,
on the 19th March 1874.
I, WILLIAM EDGAR PRALL, of the City of Washington, in the
District of Columbia, and United States of America, do hereby declare
the nature of the said Invention for "AN IMPROVED METHOD OF AND
APPARATUS FOR UTILISING COMPRESSED AIR IN THE MANAGEMENT OF RAILWAYS, IN
SIGNALLING TRAINS, ELEVATING WATER, PROTECTING TELEGRAPH WIRES, AND for
OTHER PURPOSES," to be as follows:-

page_text: for the employment of compressed air as an auxiliary in the management
of a railway, to ensure safety in the running of trains, economy in
supplying locomotives with water, protection to the telegraph wires, and
to afford motive power for various purposes. It embraces the following
several special and distinctive features which may be combined in the
one general system or be each used separately.
First. A main supply pipe extending the entire length of a railway
or of any portion thereof and kept constantly supplied with air under
"pressure by means of suitable air pumps, when combined with one or
more secondary signal pipes connected to signals arranged to be
operated by the admission of compressed air to or its exhaust therefrom,
said signal pipes being laid along those portions of the railway where
signals are required, and so connected with the main pipe and with
levers and valves or cocks arranged to be moved or shifted automatically
by passing trains that the movement of the levers and valves or cocks
shall operate to admit compressed air from the main pipe to the section
of signals on one side for the purpose of displaying or sounding said
signals, and to allow an exhaust of the air from the section of signals on
the other for the purpose of withdrawing, concealing, or silencing them;
the object of this feature of my Invention being to afford constantly
and automatically, by means of said apparatus, warning of the location
and movement of trains upon the road for any desired distance in front
and in the rear of each train through the agency of compressed air
constantly supplied as needed.
Second. An improved device (which I term a commutator") for
controlling the air supply to the signal in a pneumatic signal system
as above described, consisting mainly of suitable air passages con-
trolled by a perforated or hollow cock which is operated by a lever
so arranged that when it is thrown in one direction the air from the
main pipe through one connection will be admitted to the signal' pipo
on one side of the commutator, and when thrown in the opposite
direction it will produce the same result with reference to the signal
pipe on the other side, the cock and lever being morcover combined
with automatic valves operating to prevent an excessive consumption of
air, and so arranged in the air passages that when a communication
is established between the main pipe and the signal pipe on one side an
exhaust shall be opened from the signal pipe on the other side. and
vice versa.

page_text: :
I
Third. A single pipe conveying compressed air from a suitable air
pump or reservoir, and connected with one or more signals arranged to
be operated by an admission of compressed air into said pipe, when
combined with a valve controlling an exhaust aperture therein and
actuated by a plunger baving an enlarged area, which when exposed to
the action of a charge of compressed air admitted thereto from a
reservoir filled from said signal pipe by the operation of a lever and
valve arranged to be shifted by a passing train, shall throw open said
exhaust valve, and by permitting an escape of the air from the signal
pipe cause a reverse movement of the signals actuated thereby. The
degree of compression of the air employed to move the signals and
valves may be regulated and determined by weights or springs combined
with said valves.
Fourth. The combination of a valve controlling an exhaust aperture
in the signal pipe of a pneumatic signal system as aforesaid with the
rod actuating a signal and, with a lever to be struck by a passing train,
so that the movement of the train lever shall throw open the exhaust
valve, and the reverse movement of the signal consequent upon an
exhaust of the compressed air sustaining it shall close said valve.
Fifth. The combination with a main supply pipe charged. with con.
pressed air as aforesaid, and with one or more suitable water tanks or
reservoirs fitted with discharge pipes and inlet openings, and. by
preference arranged to be filled automatically from a suitable water
supply of an intermediate air tank or reservoir connected with the
main by a very small open pipe so as to be constantly fed therefrom
without diminishing the pressure therein, and with each tank by a
pipe sufficiently large to allow when opened a very quick or nearly
instantaneous communication of the pressure from the one tank to the
other. The object of this feature of my Invention being to obtain an
instantaneous application of air pressure to the water in the water tank
and its consequent rapid discharge therefrom when desired without
thereby materially reducing by a sudden withdrawal of the required
full supply of air therefrom the pressure in the main pipo.
Sixth. The combination of one or more telegraph wires or cables with
a continuous main pipe charged as aforesaid with compressed air, and
the support and extension of the wires or cables by means of rubber
blocks engaging the same and properly supported within the pipes or

page_text: in suitable sockets connecting them. The object of this feature of my
Invention being to ensure a more perfect insulation of the telegraph
wires and to protect them more completely from atmospheric disturbances
by enclosing them in an envelope of compressed air.
This Invention embraces also the use of the compressed air supplied
by a main pipe as herein-before described for charging as often as may.
be required tanks upon the trains to actuate the brakes thereon, for
driving stationary engines at the various stations, and in the railway
slops along the road to facilitate the travelling of freight, and for other
purposes, more especially where the air can be cheaply compressed by
means of water power.
.
'
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said William Edgar Prall in the Great Scal Patent
Office on the 18th September 1874.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, WILLIAM
EDGAR PRALL, of the City of Washington, in the District of Columbia,
and United States of America, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Nineteenth day of March, in the year
of our Lord One thousand eight hundred and seventy-four, in the
year of Her reign, did, for Herself, Her heirs and
successors, give and grant unto him, the said William Edgar Prall,
Her special licence that he, the said William Edgar Prall, his executors,
administrators, and assigns, or such others as he, the said William
Edgar Prall, his executors, administrators, and assigns, should at
any time agree with, and no others, from time to time and at all
times thereafter during the term therein expressed, should and lawfully
might make, use, exercise, and vend, within the United Kingdom
of Great Britain and Ireland, the Channel Islands, and Isle of Man,
an Invention for "AN IMPROVED METHOD OF AND APPARATUS FOR UTILISING
.COMPRESSED AIR IN THE MANAGEMENT OF RAILWAYS, IN SIGNALLING TRAINS,
ELEVATING WATER, PROTECTING TELEGRAPH WIRES, AND FOR OTHER PURPOSES,"
upon the condition (amongst others) that he, the said William Edgar
Prall, his executors or administrators; by an instrument in writing

page_text: under mis, or their, or one of their hands and seals, should particularly
describe and ascertain the nature of the said Invention, and in what
manner the same was to be performed, and cause the same to be filed
in the Great Scal Patent Office within six calendar months next and
immediately after the date of the said Letters Patent.
NOW KNOW YE, that I, the said William Edgar Prall, do hereby
declare the nature of my said 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 relates generally to a novel and comprehensive system
for the employment of compressed air as an auxilliary in the manage-
ment of a railway, to ensure safety in the running of trains, and economy
in supplying the locomotives with water, and for useful service in other
particulars.
It consists, primarily, in the use of an air main or supply pipe laid the
entire length of the railway or of any division or subdivision thereof
along which signals may be required, kept constantly filled with air
under compression by means of one or more suitable air compressing
engines and reservoirs, and communicating with a system of secondary
signal service pipes, each controlled by suitable valves provided for an
admission of compressed air thereto and its exhaust therefrom, and
connected with one or more signals arranged to be sounded or displayed by
the admission of the air to said service pipe, and be silenced or reversed
by its escape or exhaustion therefrom, or vice versa.
It consists, secondly, of improved automatic air valves or commutators
arranged to be actuated by trains passing upon the railway, and so
combined with the main air pipe and the signal service pipes as to
control the admission of the compressed air from the one to the other,
and its exhaust from the latter as herein-after set forth.
It consists, thirdly, in combining with the main air pipe and with one
or more water tanks, each provided with a suitable discharge pipe and
inlet valves, and arranged by preference to fill automatically from a
suitable source of water supply, an intermediate air tank connected with
the air main by a very small open pipe (which will permit a constant
flow of air from the main without sensibly diminishing the pressure
therein), and with each water tank by a pipe sufficiently large to allow

page_text: when opened a very quick or nearly instantaneous communication of
pressure from the one tank to the other, so as to provide for a sudden
and rapid discharge of the water from the water tank without thereby
reducing materially the pressure of air in the main pipe.
In the accompanying Drawings Figure 1 is a plan view illustrating
the relative connection of the continuous air main or supply pipe, the
signal service pipe and the commutators and signals as arranged for a
"block" system of signals upon a single track railway; Figure 2 is á
top view of my double air commutator; Figure 3 a vertical section
thereof in the line x, x, of Figure 2; Figures 4, 5, and 6 respectively
similar sectional views in the lines y, y, z, z, and w, w, of said Figure 1;
and Figure 7, a sectional view illustrating the combination of air and
water tanks with the air main and a water cistern for the purpose of
affording a water supply to the locomotives of the railway.
•
A, Figure 1, is a continuous supply pipe connected with one or more
reservoirs of air compressed by suitable machinery. This pipe may
extend the entire length of the road, and is to be kept constantly
charged with compressed air for use as herein-after described, in main-
taining automatically a constant system of train signals along the road.
The air from this pipe can be also utilised in elevating water at the water
stations and in driving machinery for various purposes, and upon many
roads may be obtained at a low cost by utilising the power of waterfalls
for its compression. I contemplate also extending a small insulated
cable covering one or more telegraph wires through this continuous
pipe to protect thereby the telegraph line from atmospheric disturbances
and save the expense incident to the exposed supports ordinarily
employed for the same. B; B', B³, are secondary signal service pipes,
each independent of the other, and which extend from one commutator
to another along the entire length of the railway where the "block
system" of signals is employed or otherwise, to extend along such
sections of the railway as may especially require signals. The
signals (C, C, Fig. 1), connected with each of the service pipes.
(B, B1, B2, &c.,) are all sounded or displayed simultaneously or nearly
so by means of the admission of a charge of compressed air to the pipe,
and are silenced or reversed by an exhaust of air therefrom. Said
signals may consist of whistles to be sounded by an admission of air to
them from the main pipe, or of flags, vanes, lights, or gates to be each
operated as required by means of a piston or diaphragm connected

page_text: therewith, and so arranged as to be moved in one direction by the
pressure of air in the signal pipe, and in the opposite direction by the
action of a weight or spring when the air pressure is removed.
The reciprocating movement imparted to the piston or diaphragm by
the application of air pressure thereto, and its withdrawal thereform may"
be applied directly to the elevation and depression of the signal, or it
may be converted by means of the usual mechanical devices into a..
rotary movement to turn the same.
D, D, (Figure 1) are automatic air valves or commutators connecting
the signal pipes B, B', B², &c., with the air main A (by means of the
branch pipes A', A¹), and with suitable exhaust vents.
Figures 2 to 6. of the Drawings illustrate the construction of my
said commutators D. When designed for use in connection with two
independent signal pipes so as to open an exhaust vent in the one
at the same instant that it admits a charge of air to the other, and
upon a single track railway where it may be operated by trains running
in opposite directions. This form of double commutator contains a
single supply valve to control the admission of air from the main
pipe to the two signal pipes. A central three-way cock whose position
determines which of the two signal pipes shall receive the charge of air
admitted from the main when the supply valve is thrown open, and two
separate exhaust valves (one for each of the signal pipes) whose move-
ments are likewise controlled by the position of the central three-way cock.
For greater.convenience the commutator may be constructed of two
divisions D¹ and D which are bolted together, as illustrated in Figures
3 to 6, the lower division projecting beyond the front face of the upper
division to form an offset, as shown in Figures 2 to 6: E, E, E, are
cylindrical chambers formed and arranged in a right line with each
other at one end of the upper division D', and which communicate
by means of enlarged central apertures formed in the partitions separating
them. E¹, E', E', are a similar series of cylindrical chambers formed.
at the other end of the division D₁; F, F', are passages forming respec-
tively a communication between the lower chamber in each series-with
the signal pipe B' and B² at its appropriate end; G, Gi, are passages
connecting the two central chambers with an outward exhaust.vent, as
herein-after more fully described; a, a¹, are valves of rubber placed in
the lower chambers to close the openings between the lower and central

page_text: chambers on each side, free communication being otherwise established
between the respective signal pipes B and B through the passages F, F¹,
and the exhaust passages G, G¹, respectively, whenever one or the other
of the said exhaust valves a, a¹, are opened; I, I, are pistons working
closely within the two upper chambers, and K, K', are central rods
connecting the pistons with the valves a, a, respectively, said valves
being secured centrally thereto, substantially as shown in the Figs.
3 and 6. The rods K, K¹, are so adjusted in length as that when either
piston is depressed its valve will be thrown open, and vice versa. Elastic
or flexible diaphragms may be substituted for these pistons I, I'.
.
The piston and connecting rods K, K', are elevated, and the exhaust
valves automatically closed by means of springs u, u, arranged within
the central chambers and secured to the rods K, K¹; b, b, are plugs to
close the upper chambers E, E¹, after the pistons I, I', have been
inserted therein; H, H, are two superimposed connecting chambers
formed centrally in the lower portion of the division D³ of the commu-
tator (see Fig. 5), and i is a rubber valve arranged in the lower
chamber H to close the opening between the two; P is a rod secured
centrally to the valve i, and extending upwardly and outwardly through
suitable bearings formed to receive it, and centrally through, a third
chamber H³ formed in the upper part of the division D², as shown in
Figures 4 and 5; s is an outward exhaust vent pierced laterally in the
lower end of said chamber H³, and is a perforated plunger secured to
the rod P and working in the chamber, so that when forced down it
shall partially close the exhaust vent s. The exhaust passages G, G¹,
both communicate with said chamber H³ above the plunger ", as
shown in Figure 4 and 5. The air main A is made to communicate
directly with the lower chamber H, its communication with the second
chamber H being controlled and closed by means of the supply valve i,
as shown in Fig. 4; M (Figs. 3 and 4) is a hollow cock turning freely
in a suitable seat or bearing formed transversely in the upper division D¹
midway between the exhaust valve chambers E, E¹, c (Fig. 4) being a
plug closing the rear end of the cock; N is a passage way extending
from the lower portion of the seat of the cock to the chamber H¹ of
the supply valve, and communicating through it with the air main A
(see Fig. 4); L, I, are openings or passage ways affording communi-
cation respectively between the seat of the cock N and the passages
F, F, to the signal pipes B¹, B², as shown in Figure 3. These openings

page_text: are controlled by valves J, J, opening inward toward said passages F, F¹,
so as to permit a free flow of air into the passages, but prevent its
return therefrom; m, m³, are openings made in the perimeter of the
hollow cock M in such relative positions as that when the opening m
is in register with the opening L¹ into the signal pipe passage F¹ on one
side, the opening L into the passage F on the other will be closed, and
vice versa, as shown in Fig. 3; e is a notch or recess cut in the upper
side of the cock of such a width and depth as that, whether the cock
is turned to close either the aperture L or the aperture L', said recess
shall be in register with a small central vent passage f pierced outwardly
therefrom through the upper division D₁ of the commutator, and with
one or other of two secondary passages 9, 9', pierced obliquely through
said division from the cock to the upper chambers E, 'E', of the exhaust
valves respectively, said notch e thus serving to establish communication
between the central outward vent or passage fand that one or other
of said chambers E, E', containing the piston of the exhaust valve which
needs to be closed. A third opening n is cut, in the perimeter of the
hollow cock M of such width as that whether the cock be turned to
uncover either opening L or L' it shall always be in register with the
supply passage N; t is a stom projecting outwardly from the face of
the cock M, as shown in Figure 4, in a right line intersecting that of the
projecting valve rod P.
Q is a lever whose lower end is made to encircle the stem / (see Fig. 5)
and which turns freely thereon, and whose upper end projects above the
commutator so as that it may be struck by a finger arranged to project
for the purpose from the locomotives or carriages of the railway. The
upper end of the valve rod P terminates in a yoke, which when the rod
is clevated closely encircles the lower end of. the lever Q, as shown in
Figure 5. The ends of the yoko bear closely against cars or lugs q, q',
projecting from either side of the lever, so that when the rod P and its
yoke is elevated the lever is carried up and sustained in an upright
position, as shown in Fig. 5, and when the lever is thrown over to onc
side or the other it will bear down the rod P. Pins v, v¹, project from
the face of the cock on each side of the lever Q in such position
relative thereto as that the pin von the side nearest that aperture or
way L, which is closed, shall when the lever is upright be in contact
therewith, the other lug being so far removed therefrom as not to come
into contact until the cock. has been turned far enough to open said

page_text: .
closed aperture L, and close that (L') which had until then remained open.
d, d, are cocks controlling small outward exhaust vents pierced in the
upper piston chambers E and E¹ of the exhaust valves in the commu-
tators to allow a gradual escape of the air admitted thereto after it shall
have forced down the piston and opened the exhaust valve. So soon as
the air has exhausted from either chamber through its said vent the
resilient power of the spring u will automatically carry up and close the
exhaust valve a. With a commutator thus constructed and its main
supply pipe A properly charged with compressed air the pressure of the
air from the main against the valve i will tend to keep it tightly closed
(see Fig. 4) and force up the rod P and its yoke against the lugs q, q',
on the lever Q so as to maintain the latter in an upright position, as
shown in Figure 5. If now the lever be struck by a train (passing for
example in the direction indicated by the arrow in the Drawing,
Figure 5), and thrown into the position indicated by the dotted lines,
Fig. 5, the lever in its movement will bear against the pin o' projecting
from the cock M, and turn said cock so as to establish communication
through it between the air supply passage N.and the signal pipe passage
F', as shown in Figure 3, and simultaneously. by the pressure of its
lug q upon the corresponding side of the yoke will force down the rod P,
and thereby open the valve i and admit à volume. of compressed air into
the air passage N, as indicated by the arrows in Fig. 4. The charge of
compressed air thus admitted to the passage N following the communi-
cation established through the cock M by means of the openings n and m'
therein will pass (see Fig. 3) into the passage F¹ to the signal service
pipe B, and operate to throw up all the signals connected therewith, the
opposite end of said pipe being closed by a valve a in the commutator
connected with that end. So soon as the passages N and F¹ and the
signal pipe B have thus become fully charged with compressed air from
the main the pressure of this air exerted outwardly upon the area of the
valve rod P. will automatically force up said rod and close the supply
valve a¹ and throw the lever Q back to its upright position. To prevent
too sudden a close of the valve i I combine a weight 10 therewith (see
Figure 4), and by varying the size of this weight the degree of pressure
required to close the valve i, and consequently the degree of pressure of
air admitted to the signal pipe, may be adjusted and determined with
precision. A like adjustment may be made by varying the diameter of
the rod P, as at p in Figures 4 and 5.
It will be observed that the automatic return of the lever Oto it's

page_text: upright position under the influence of the outward movement of the
valve rod P will not operate to turn or move the cock M; and that
the communications established through it, will consequently remain
unchanged until the lever is thrown in the opposite direction. Hence
if a second locomotive follow the first in the same direction, and the
lever is therefore thrown over in the same direction as before, the effect
will only be to admit a second charge of compressed air to follow the
same course as that before admitted. Thus the primary effect of a move;
ment of the lever Q in either direction is to admit compressed air to the
signal pipe on that side, and to display all the signals connected with
said pipe; but simultaneously the same movement of the lever effects a
second result, viz., the discharge of the air from the service pipe which
has been passed by the train before reaching the commutator, and
consequent reversal of all the signals connected therewith. This result
is accomplished by the passage of a portion of the compressed air
admitted to the passage N by the opening of the supply valve i up
through the cock M, its aperture m, and the communicating passage g¹
into the upper piston chamber E of the exhaust valve a. This charge of
air bearing upon the piston I will force it down, as illustrated in Fig. 3,
and thereby throw open the exhaust valve à, and allow the air in the
pipe B and its passage way F, by which the signals were maintained, to
escape frcely through said valve opening into the passage G, and out
through the vents in which the passage terminates. The vents is so
far closed by the perforated plunger r, when the air supply valve is
thrown open, as that the air admitted to the chamher H³: from the
exhaust passage G, as just described, will bear temporarily upon the rod P
to force it downward, and consequently hold the valve i open until an
equilibrium of pressure is attained in the two chambers H3 and H³. The
same effect may be produced by reducing the size of the perforations in
the plunger v, so as to partially confine the air escaping through the
same. The plunger may however be entirely dispensed with, and a
simple cock be combined with the vent s to regulate the exhaust of the
air, and its pressure upon the rod P; or the exhaust may be left entirely
free, and be made without reference to the rod P, in which case the
passages G, G¹, are not needed, simple open vents being substituted
therefor.

page_text: piston chamber is opened, which by regulating the rapidity with which
the air (whose pressure upon the piston I serves to keep the valve open)
shall exhaust will operate to control the time within which the pressure
shall be so far reduced as to allow the spring u to close the valve.
As the lever Q is automatically thrown up so soon as sufficient air has
entered either signal service pipe (for example B²) to throw up its
signals, it is at once ready for operation, either to throw a second charge
of air to the same pipe (B²), as above described; or if struck by a train
coming from the opposite direction to reverse the cock, and consequently
admit air to the pipe B¹ and permit an exhaust of air from the pipe B².
A locomotive passing to and fro upon the road will thus surely cause
a display of the signals in advance of it by an admission of air to the signal
pipe extending in advance, and as surely cause those already displayed,
and which it has passed, to drop, by permitting an exhaust of air from the
signal pipe left behind; the signals which are displayed along any one
signal pipe remaining so until the train has reached the next section.
It is evident that where, as in a double-track railway, the trains
invariably pass over a given track in one direction only, a reversing
cock M is not required in a commutator for operating tho signals, and
that but one exhaust valve is needed therein.
.
In Figure 7 of the Drawings, S is a water tank, which may be sub-
merged in a cistern, well, pond, or running stream, or otherwise placed
so that water may naturally flow into and fill the same when empty
through a pipe or an opening T fitted with a valve to permit a free
ingress of the water but prevent its reflow. By burying or submerging
the tank it is protected from all exposure to frost. U is a discharge pipe
opening into the tank near the bottom thereof, and extending upward
either to connect with a water crane on the railway or to be carried to any
other desired point. V is an air tank of such size with relation to the
water tank S as that it will in itself hold a quantity of compressed air
sufficient to force out and discharge all the water in the water tank, the
relative proportions of the two differing necessarily with the degree to
which the air is compressed. W is a small open pipe connecting the air
tank V with the main pipe A, and which is of such a reduced diameter as
that a flow of air through the same from the main pipe cannot be rapid
enough to materially reduce the pressure in said main whilst the air com-
pressor is in operation. R is the air compressing engine for maintaining
a pressure of air in the main pipe A, X is a larger pipe closed by a

page_text: three-way cock and connecting the air tank V with the water tank S,>
and of such proportions as that when opened it will permit a quick.
passage of the air from the tank V. to the tank. S, so. that the full
pressure in the former may be instantly communicated to the latter upon
opening the valve. Y is a three-way cock placed in the pipe X, and so
arranged as that when communication between the tanks V and S is.
thereby closed communication will be established between the tank Sand
the outer air, so as to allow a quick free exhaust of air from the tank,
which said communication will in turn be closed by the movement of tho'
cock to open the pipe X. The cock Y may be arranged to be operated'
by a lever Z or otherwise from a point convenient to the water crane.'
With the apparatus thus constructed it is only necessary to turn tho
cock Y to admit a flow of the compressed air in the tank V into tho
tank S. Its pressure upon the surface of the water will thereupon
operate to close the check valve in the supply pipe T and force the water
out through the discharge pipe. U to its full capacity. So soon as a suffi-
cient quantity of water has been drawn from the tank S and the cock Y is
closed the closing of the cock will permit an exhaust of the compressed
air remaining in the tank and allow a supply of water to flow in through
the pipe T to refill it. So soon as air is drawn as above from the tank F
a supply commences to flow thereinto from the main A' and tho
flow continues until the tank is filled again, although in consequence of
the small diameter of the connecting pipe W the operation is made so
gradually as not to reduce materially the pressure in the main.
tho
I contemplate combining two or more air tanks with a single water
tank, so that when it is necessary to empty the latter oftener than the
gradual filling of a single air tank will allow without too great delay,
required charge of compressed air may be drawn from the one while the
other is yet filling. It is also evident that two or more water tanks may
in like manner.be combined with a single air tank to save delay where
the flow of water is slow at the desired point.
I do not claim as new the use of compressed air for operating railway
signals nor for expelling water from a self-filling water tank, but I claim
as my Invention,
1. The combination of a continuous air reservoir or main supply pipe A
with a railway, and with a system of signal service pipes B, B¹, con
trolled by suitable supply and exhaust valves, and arranged to be charged
with air from said main pipe as required for the purpose of displaying

page_text: or sounding cautionary signals, substantially in the manner herein set
forth. :
.
2. A valve combined with an air pressure pipe A, an air service pipe
or passage N, and a plunger rod P extending outwardly from the valve
chamber, and operating automatically to close the valve i, substantially 5
as and for the purpose herein set forth.
t
3. An exhaust valve a combined with an air pipe or passage F, an
escape vent or passage G, and a piston I of enlarged area playing in a
chamber E open at one end and communicating with an air pressure pipe
or passage g' at the other, substantially in the manner and for the purpose 1
herein set forth.
4. The cock M, constructed and operating substantially as described
in combination with the air passages L, L', N, f, g, and g¹.
5. The lever Q and its lugs q, q, in combination with the cock M and
its projecting pins v, v', and with the forked end or yoke of the rod P,. 1
substantially as and for the purpose herein set forth.
6. The combination substantially as herein described of one or more
water tanks S provided with suitable discharge pipes and inlets, with an
extended pipe or main A to be kept charged with compressed air, and
with one or more intermediate air tanks V, each connected to the main 2
pipe A by a pipe W of so small a diameter with reference thereto as that
the constant pressure maintained therein will not be materially reduced
by the escape of air through said connecting pipe substantially as herein
set forth.
In witness whereof T the soid William Dimon Dall 1