IMPROVEMENTS IN DOCK GATES AND CAISSONS FOR CLOSING THE ENTRANCES TO DOCKS AND BASINS
Year: 1869

page_text: LETTERS PATENT to Edward Finch, of Beaufort Square, Chepstow, in
the County of Monmouth, for the Invention of "IMPROVEMENTS IN
DOCK GATES AND CAISSONS FOR CLOSING THE ENTRANCES TO DOCKS AND
BASINS."
Sealed the 26th April 1870, and dated the 3rd November 1869.
PROVISIONAL SPECIFICATION left by the said Edward Finch at
the Office of the Commissioners of Patents, with his Petition, on
the 3rd November 1869.
I, EDWARD FINCH, of Beaufort Square, Chepstow, in the County of
5 Monmouth, do hereby declare the nature of the said Invention for
"IMPROVEMENTS IN DOCK GATES AND CAISSONS FOR CLOSING THE ENTRANCES TO
DOCKS AND BASINS," to be as follows:-
This Invention has for its object improvements in dock gates and
caissons for closing the entrances to docks and basins.

page_text: In the construction of caissons and buoyant dock gates it has been
usual to admit water into them to regulate and adjust the amount of
buoyancy they shall possess, and when admitted to close the aperture or
valve through which it has entered, and when the quantity has become
in excess of what is required or has increased by leakage or when it is
required to empty the caisson or gate of water so admitted it has been
usual to pump it out either in part or wholly as may have been required
by means of force or lift pumps.
According to my Invention I form the caisson or dock gate in such
manner as to be able to admit water through holes or through a valve or
cock in the bottom or lower part of the caisson or dock. The upper part
of the same above the water I make air-tight, so that as the water is
admitted the air in this upper part or chamber becomes compressed
or by opening a cock is allowed to escape. When I want to regulate
the buoyancy of the caisson or gate or empty it of water I close this
cock and open another which shall be connected by pipes or flexible
hose to a chamber of compressed air or an air pump, and by either of
these means compress air into the space above the water and thus
drive or force out the water through the holes, cock, or valve through
which it entered at the bottom, and thus regulate the depth of immersion
of the dock gate or caisson in the water, or, if need be, drive out the whole
of the water.
This Invention also consists in forming caissons for closing the
entrances of docks and basins with shoulders, one at each end, to rest
on shelves formed in the masonry at the two sides of the entrance to
the dock or basin.
When it is desired to close the dock passage with the caisson it is
brought floating sufficiently high for the shoulders to come above the
shelves. Air is then allowed to escape from the upper chamber of the
caisson and water to rush in at the bottom until the shoulders rest upon
the shelves made to receive them. As the tide recedes the water in the
dock presses against the caisson and causes it to slide on the shelves
until the timber facing with which the caisson is furnished as usual
presses against the masonry like a valve to its seat.
For the convenience of stowing away the caisson when not required
or when ships are passing, there is a recess formed in the masonry
having similar shelves to those described above to receive the shoulders

page_text: of the caisson; in this recess it can remain perfectly safe whether there be
water in the dock passage or not.
The upper surface of the shelf and the under surface of the shoulders
on the caisson may be fitted with metal plates planed truly so that the
shoulders may slide freely over the shelves, or friction rollers may be
employed to reduce friction.
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said Edward Finch in the Great Seal Patent Office
on the 3rd May 1870.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, EDWARD
FINCH, of Beaufort Square, Chepstow, in the County of Monmouth, send
grecting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Third day of November, in the year
of our Lord One thousand eight hundred and sixty-nine, in the
thirty-third year of Her reign, did, for Herself, Her heirs and successors,
give and grant unto me, the said Edward Finch, Her special licenco
that I, the said Edward Finch, my executors, administrators, and
assigns, or such others as I, the said Edward Finch, my 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 "IMPROVEMENTS
IN DOCK GATES AND CAISSONS FOR CLOSING THE ENTRANCES TO DOCKS AND BASINS,"
upon the condition (amongst others) that I, the said Edward Finch, my
executors or administrators, by an instrument in writing under my,
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 Seal Patent Office within six calendar months next and imme-
diately after the date of the said Letters Patent.
NOW KNOW YE, that I, the said Edward Finch, do hereby declare
the nature of the said Invention, and in what manner the same

page_text: is to be performed, to be particularly described and ascertained in
and by the following statement thereof, that is to say :-
This Invention has for its object improvements in dock gates and
caissons for closing the entrances to docks and basins.
In the construction of caissons and buoyant dock gates it has been
usual to admit water into them to regulate and adjust the amount of
buoyancy they shall possess, and when admitted to close the aperture or
valve through which it has entered, and when the quantity has become
in excess of what is required or has increased by leakage or when it is
required to empty the caisson or gate of water so admitted it has been
usual to pump it out either in part or wholly as may have been required
by means of force or lift pumps.
According to my Invention I form the caisson or dock gate in such
manner as to be able to admit water through holes or through a valve or
cock in the bottom or lower part of the caisson or dock; the upper part
of the same above the water I make air-tight so that as the water is
admitted the air in this upper part or chamber becomes compressed,
or by opening a cock is allowed to escape. When I want to regulate
the buoyancy of the caisson or gate or empty it of water I close this cock
and open another, or I use a three-way cock, which answers the purpose
of the two cocks, which shall be connected by pipes or flexible hose
to a chamber of compressed air or an air pump, and by either of these
means compress air into the space above the water, and and thus drive
or force out the water through the holes, cock, or valve through which
it entered at the bottom, and thus regulate the depth of immersion of
the dock gate or caisson in the water, or, if need be, drive out the
whole of the water.
This Invention also consists in forming caissons for closing the
entrances of docks and basins with shoulders, one at each end, to rest on
shelves formed in the masonry at the two sides of the entrance to the
dock or basin.
When it is desired to close the dock passage with the caisson it is
brought floating sufficiently high for the shoulders to come above the
shelves; air is then allowed to escape from the upper chamber of the
caisson, and water to rush in at the bottom until the shoulders rest upon
the shelves made to receive them. As the tide recedes the water in the
dock presses against the caisson, and causes it to slide on the shelves

page_text: metal surface of the shelf when required to do so; I represents a three-
way cock, which is worked by the lever K acting upon the spur wheels,
as shewn.
Figure 2 shews an end view of the caisson; Figure 3 shews a vertical
section of the caisson on the centre line; Figure 4 shews a horizontal
section at C, D; Figure 5 shews a horizontal section at E, F; Figure 6
shows a plan of the top or deck of the caisson.
Figures 7 and 8 show enlarged detail Drawings of the three-way cock.
Lis the nozzle upon which the union joint which connects the hose pipe
from the air pump or accumlator with the caisson is applied; M is the
pipe through which the compressed air passes into the caisson or through
which it is allowed to issue out of the caisson according as the plug of
the three-way cock is turned; N is the pipe through which air liberated
from the caisson has to escape; O is the plug of the cock; and forming
part of it at the outer or front end is a shaft upon which a spur wheel is
firmly keyed, and by means of which the caisson is worked, as shewn
in the Figures previously explained.
Figure 9 shows the three-way cock in section and the plug that works
within it. This Figure represents the passage for air open from the air
pump or accumulator to the caisson. If the plug of the cock is turned
round one fourth of a circle from 1 to 2, the communication with the air
pump is cut off, and one will be made from the caisson to the escape
pipe, and so long as the plug of the cock is in this position the air in the
caisson will rush out. If the plug of the three-way cock is turned another
quarter of a circle in the same direction from 2 to 3 the communication
with the air pump or accumulator will still remain closed, and the com-
munication between the caisson and the escape pipe will also be closed.
This caisson is intended to be used for retaining or keeping back
water in docks and other similar places. It is adapted for the largest
or smallest passages through which vessels may have to pass and answers
all the purposes of ordinary gates of a caisson and of a bridge. It is
requisite to state that suitable preparations in the masonry will have to
be made to receive the caisson both when doing duty in its place and
also when removed and put aside to allow vessels to pass.
These preparations are as follows:-The caisson when in action presses
against a ledge in the masonry round the invert and up the sides of the
passage or lock. It is essential that this ledge should be dressed true, so
that the timber facing on the caisson should when pressed by the water

page_text: in the dock against it make a water-tight joint. As the caisson when in
place rests upon and is supported by two shelves formed in the masonry
it is necessary to prepare them, and as it is made to slide on these shelves
they should have upon them metal surfaces planed smooth and suitable
for the purpose. When the caisson is removed to allow vessels to pass. it is
placed in a recess in the masonry, and this also should have shelves for it
to rest upon until required again: to close the entrance. This recess will
consequently have to be prepared. This is all that need be said about the
masonry.
The pneumatic caisson is made of wrought iron, and has one flat side
of a shape corresponding with the shape of the invert and sides of the
lock or passage it has to close, except that it has a margin or rim beyond
this, upon which wood is carefully attached, and it is by bringing this
margin with wood' surface against the ledge formed in the stonework
that a perfectly water-tight joint is made when the pressure of water
retained in the dock is brought to act against the back of the caisson.
It is box-like in. shape longer by the width of the wood margin on both
sides than the opening it has to close, and deeper by the wood margir
that is intended to press against the ledge at the invert. From front to.
back the width must be sufficiently great to give it the requisite strength
to bear the pressure of water brought against it. It must be made
perfectly air and water tight except at the bottom, and this is to be per-
forated with a number of small holes or fitted with a valve or cock. It.
is made to retain a vertical position when floating by having iron ballast.
fastened into the bottom of it. It is constructed with shoulders which
overhang the sides, as the Drawing will make clear, the under sides of.
which are provided with planed metal surfaces. In a convenient position
at or near the top of this caisson the three-way cock is placed.
From Figures 1 and 3 it will be seen that the caisson is constructed
of plates of wrought iron, the joints of which run horizontally in straight
lines from side to side. At the lower part these joints are formed by the
edges of the plates after being planed true, being butted upon and
rivetted to horizontal bars of T iron placed in the inside of the caisson..
In the upper part of the caisson plain strips of flat iron are used instead
of T irons to form the joints upon. At the lower part where the strain
is greatest the strength of the plates is supplemented by angle and
reverse angle irons; higher up where the strain is less single angle irons.
are used. The angle irons, T irons, and strips all run horizontally and in

page_text: a line with the joints of the plates. The two sides of the caisson are
kept asunder and sustained in position by frames and cross beams placed
at intervals, and which also strengthen the top and bottom of the caisson.
The bottom and sides have additional strength given to them by angle
irons which are placed on the outside of the caisson, and the top or deck
plate is also strengthened by angle irons placed outside, to which the
roadway is attached, as shown. At the bottom of Figure 3 the timber
attached to the margin of the caisson is shown pressing against the
masonry of the invert.
The position and number of the frames that keep the front and back
of the caisson asunder are shown at Figure 4, and how they are attached
to the horizontal angle irons; it also shows the angle irons outside that
strengthen the ends and plates that are at intervals introduced in the inside
to further strengthen them. The wood is also shown on the margin that
presses against the ledge in the masonry to form the water-tight joint.
Figure 5 illustrates how the shoulder is made, and shows plan of the
iron plate to which the metal plate having the planed sliding surface is
bolted, and how the timber margin above the shoulders presses against
the masonry and forms the water-tight joint. It also shows the position
of the three-way cock and how it is attached to the caisson.
Figure 6 shows how the roadway and parapet are formed and the
position of the wheel connected with that on the caisson for working the
three-way cock. I must state that an air pump is requisite either fixed
on the caisson and attached to the three-way cock before named or
communicating with the three-way cock from the shore, by flexible hose
pipe. For large openings an air chamber placed at any convenient
distance may be used to advantage, into which the pump may for any
requisite time be at work accumulating a reservoir of compressed air
available at any moment to any necessary extent by means of flexible
hose conveying it to the three-way cock on the caisson.
I will now go through the process of bringing the caisson from where
it has been constructed, putting it in place, and working it afterwards.
The caisson will be built near the water side on the flat with the face
upwards, so that the timber margin that is intended to press against the
masonry and form the water-tight joint may be well and accurately
attached and dressed off true. When completed it will be tested to
prove that it is all over perfectly air and water tight, with the exception
of the perforations in the bottom. These perforations are then to he

page_text: closed in a temporary manner and the caisson launched or floated into
the water. With a little trimming it will be made to swim on the
flat, and in this state towed any distance to its destination, where it
should arrive at high water. The perforations at the bottom should then
be opened and the water allowed to flow in. The bottom of the caisson
being the heaviest, as the water enters it will gradually sink until the
perforations are under water, and the air in the inside of the caisson is
so compressed as to balance the pressure of the water without. It will
then be necessary to open the three-way cock at the top of the caisson
to the atmosphere, and thus allow the pent up air to escape and the
caisson to sink vertically until it is immersed to a convenient depth
to be handily moved about; the three-way cock must then be closed to
prevent a further escape of air and to keep it from sinking deeper.
Floating still it must now be moved to the opening it is intended to
close with the planed surfaces on the under side of the shoulders hovering
immediately over the planed metallic surfaces on the two shelves of the
masonry. When adjusted to position the three-way air cock is again
opened, air escapes and the caisson gradually sinks in the water until
the planed surfaces under the shoulders come in contact with, take their
bearing and rest upon the planed metallic surfaces on the shelves. The
margin of the caisson covered with wood is then immediately opposite
the ledge prepared in the masonry round the invert and up the sides of
the passage.
As the tide recedes from the front side of the caisson the
pressure of water at the back causes the shoulders to slide on the shelves
of the masonry until the timber margin of the caisson comes up to and
presses against the ledge in the masonry; thus the opening is closed and the
water-tight joint is made. When the tide has gone out to its full extent
it will be well to place in the bottom of the caisson some cast-iron balls
as ballast; these in all future operations will cause the caisson to move
steadily when floating in the water, and will at the same time allow frec
ingress and egress for the water through the perforations in the bottom.
The caisson as so far described has closed the passage and is keeping
back the water in the dock or lock behind it while the tide recedes.
When the tide makes again the next process is to remove the caisson in
proper time so as to admit vessels in or out of the dock. As soon as the
tide outside has risen to the height of the water that has been pent up by
the caisson in the dock or lock a communication is made with the air
pump direct or by means of the flexible hose with the air accumulator

page_text: and the three-way cock at the top of the caisson; this cock is so turned
as to allow the compressed air free access into the caisson, this forces
the water out through the perforations in the bottom and causes the
caisson to rise and float. The cock is closed and the caisson is then frec
to be moved out of the way to the recess in the masonry provided for it.
It is then brought with the shoulders hovering again over shelves pre-
pared to receive them, the three-way cock is again turned in a direction.
to allow air to escape, the caisson sinks until its shoulders take a steady
bearing on the shelves, the cock is again closed, and the caisson is safely
at rest. When the vessels have all passed and it is time to close the
passage communication is again made by means of the three-way cock on
the caisson with the air pump or air accumulator, the eompressed air
as before rushes in and drives the water out of the caisson through the
perforations in the bottom, it again floats free and the cock is closed; it
is then moved to the passage as in the first instance described, and when
adjusted the three-way cock is turned so as to allow air to escape out of
the caisson until it gradually sinks, the shoulders taking their bearing on
the planed surfaces of the shelves, and as before when the tide begins to
recede the pressure of the water in the dock or lock against the back of
the caisson causes the shoulders to slide on the shelves of the masonry
until the wood margin of the caisson presses against the ledge in the
stonework; the water in the dock is thereby retained.
All future operations are repetitions of those described. I may now
speak of the merits of the pneumatic caisson :-
1st. It is simple in form, and can therefore be easily and cheaply con-
structed.
2nd. There is no machinery of any kind about it to get out of order.
3rd. Being made entirely of wrought iron any required strength may
be given to it.
4th. As the water-tight joint is made by the direct pressure of a flat
surface of wood against a corresponding flat surface of stone, and as this
surface of wood is brought parallel and at once against the stone by the
slightest pressure being brought against the back of the caisson accuracy
of bearing and a perfectly water-tight joint is ensured.
5th. By the shoulders of the caisson being brought to rest upon the
shelves of the masonry, and by the two surfaces which come in contact

page_text: being planed smooth and lubricated, the caisson slides to its place with
great ease and always comes to one and the same position.
6th. As any injurious leakage will be of air from the upper portion of
the caisson this can at all times be discovered and prevented.
7th. As in working the caisson water is required to be admitted and
expelled alternately through the perforations at the bottom there will
never be any deposit of mud in the caisson however dirty the water may
be in which it is used.
8th. As the caisson will be completely afloat always when it has to be
moved, a comparatively small amount of power will only be requisite to
shift it from the passage it has closed to the recess prepared for it when
not in use, and to remove it back from this when the passage is
required to be closed again.
9th. By fixing a floor, parapet, and railway on the top of the caisson it
will form a bridge to carry any requisite weight.
10th. Sluices may be made through the caisson worked in the usual
way for scouring purposes or for lowering the water in the dock behind
the caisson.
11th. As the caisson has a flat bottom intended to be properly protected
it can be removed at any time to any place having a flat surface for it
to rest upon, and can there be placed standing upright and the water be
allowed to leave it.
12th. If occasion should occur for a caisson to be removed and
another substituted no delay whatever need take place in making the
change.
As compared with gates it has no hollow quoin to make tight, no heel
post pivot or top straps to contend with, no rollers or roller paths to get
out of order, no friction of any kind to overcome beyond that which is
produced by its being moved while afloat through the water, all
powerful crabs and strong chains and chain rollers are dispensed with. A
few warps and a capstan or two of small power either on the caisson or
on shore is all that is required.
As compared with an ordinary caisson the penumatic caisson always
frees itself from mud, the water being admitted and expelled through the
bottom; the ordinary caisson on the contrary admits the water and has it
pumped out when required, the consequence is all the mud in the water
is deposited at the bottom of the caisson and has to be dug out. This

page_text: caisson slides freely on its shoulders to its place; the ordinary caisson has
its bearing at the bottom and sides and requires therefore great force to
press it to its bearing, and it is unwieldly and unmanageable. My
caisson is as manageable as a boat and can be made to. do. all you will it.
The accumulator is a cylindrical chamber of wrought iron, and may be
placed in any convenient out of the way place at any distance from tho
dock entrance. A small steam engine may be employed for any requisite
length of time in forcing air into this chamber or reservoir of
power, from
which a pipe must be laid to a convenient position near the caisson; here
a cock will be placed upon which by a union joint one end of a length
of flexible hose will be attached, whilst the other end will connect with
the three-way cock on the caisson; by this means communication will be
made with or cut off from the accumulator, and thus the caisson may
when required be made expeditiously buoyant. The compressed air in
the accumulator may be used to work crabs or capstans for moving the
pneumatic caisson or other purposes.
If thought expedient the surfaces under the shoulders of the caisson
and the surfaces on the shelves may be made oblique, falling towards the
recess in the masonry, so that when the caisson is brought to bear on the
shelves the weight given to it will at once bring it up to the recess in the
masonry and cause the water-tight joint at once to be made without
waiting for the tide to fall and pressure to come from behind.
Buoyant dock dates may be similarly constructed, but I prefer to
employ caissons capable of being floated freely from place to place..
Old caissons and hollow lock gates may frequently be advantageously
altered in accordance with my Invention.
Having thus described the nature of my said Invention, and the manner
of performing the same, I would have it understood that what I claim
is,—
First. The construction of hollow caissons and dock gates with per-
forations or entrances at the bottom of them or thereabouts to allow
water to come in and be driven out of them, all other parts being made-
air and water tight so that they may be floated by forcing air into them
and allowed to settle down into their scats by permitting the air to
escape, substantially as herein described.
Second. I claim the construction of hollow caissons and dock gates
with shoulders upon them, which shoulders are caused to rest and move

page_text: on shelves provided in the masonry to receive them, substantially as
hercin described.
Third. I claim the construction of hollow caissons and dock gates,
substantially as herein described.
In witness whereof, I, the said Edward Finch, have hereunto
set my hand and seal, this 26th day of April, in the year of
our Lord One thousand cight hundred and seventy.
EDWARD FINCH. (L.S.)