THE LOCK MACHINERY
One of the problems that had to be solved before the Panama Canal
could be presented to the American people as a finished waterway, was
that of equipping it with adequate and dependable machinery for its
operation. Panama canals are not built every year, so it was not a
matter of ordering equipment from stock; everything had to be invented
and designed for the particular requirement it was necessary to meet.
And the first and foremost requirement was safety. When we look over
the canal machinery we see that word "safety" written in every bolt,
in every wheel, in every casting, in every machine. We see it in the
devices designed for protection and in those designed for operation as
well. We see it in the giant chain that will stop a vessel before it
can ram a gate; we see it in the great cantilever pivot bridges that
support the emergency dams; we see it in the double lock gates at all
exposed points; we see it in the electric towing apparatus, in the
limit switches that will automatically stop a machine when the
operator is not attending to his business, in the friction clutches
that will slip before the breaking point is reached. Safety, safety,
safety, the word is written everywhere.
The first thing a ship encounters when it approaches the locks is the
giant chain stretched across its path. That chain is made of links of
3 inches in diameter. When in normal position it is stretched across
the locks, and the vessel which does not stop as soon as it should
will ram its nose into the chain. There is a hydraulic paying-out
arrangement at both ends of the chain, and when the pressure against
it reaches a hundred gross tons the chain will begin to pay out and
gradually bring the offending vessel to a stop. After a ship strikes
the chain its momentum will be gradually reduced, its energy being
absorbed by the chain mechanism. While the pressure at which the chain
will begin to yield is fixed at 100 gross tons, the pressure required
to break it is 262 tons. Thus the actual stress it can bear is two and
a half times what it will be called upon to meet. The mechanism by
which the paying-out of the chain is accomplished is exceedingly
ingenious. The principle is practically the reverse of that of a
hydraulic jack. The two ends of the 428-foot chain are attached to big
plungers in the two walls of the locks. These plungers fit in large
cylinders, which contain broad surfaces of water. They are connected
with very small openings, which are kept closed until a pressure of
750 pounds to the square inch is exerted against them. By means of a
resistance valve these openings are then made available, the water
shooting out as through a nozzle under high pressure. This permits the
chain plunger to rise gradually, while keeping the tension at 750
pounds to the inch, and the paying-out of the chain proceeds
accordingly. Of course not all ships will strike the chain at the
same speed, and in some cases the paying-out process will have to be
more rapid than in others. This is provided for by the automatic
enlargement of the hole through which the water is discharged, the
size of the hole again becoming smaller as the tension of the chain
decreases. This chain fender will stop the _Olympic_ with full load,
when going a mile and a half an hour, bringing it to a dead standstill
within 70 feet, or it will stop an ordinary 10,000-ton ship in the
same distance even if it have a speed of 5 miles. The function of the
resistance valve is to prevent the chain from beginning to pay out
until the stress against it goes up to 100 tons, and to regulate the
paying-out so as to keep it constant at that point, so long as there
is necessity for paying-out. Any pressure of less than a hundred tons
will not put the paying-out mechanism into operation.
When a ship is to be put through the locks the chain will be let down
into great grooves in the floor of the lock. There is a fixed plunger
operating within a cylinder, which, in turn, operates within another
cylinder, the resulting movement, by a system of pulleys, being made
to pay out or pull in 4 feet of chain for every foot the plunger
travels. The chain must be raised or lowered in one minute, and always
will have to be lowered to permit the passage of a ship. The fender
machines are situated in pits in the lock walls. These pits are likely
to get filled with water from drippings, leakages, wave action, and
drainage, so they are protected with automatic pumps. Float valves are
lifted when the water rises in the pits. This automatically moves the
switch controlling an electric motor, which starts a pump to working
whenever the water gets within 1 inch of the top of the sump beneath
the floor of the pit. Twenty-four of these chain fenders are required
for the protection of the locks, and each requires two such tension
machines.
No ship will be allowed to go through the canal except under the
control of a canal pilot. He will certainly bring it to a stop at the
approach wall. But if he does not, there is the chain fender. There is
not a chance in a thousand for a collision with it, and not a chance
in a hundred thousand that the ship will not be stopped when there is
such a collision.
But if the pilot should fail to stop the ship, and it should collide
with the fender chain, and then if the fender chain should fail to
stop it, there would be the double gates at the head of the lock.
There is not one chance in a hundred that a ship, checked as it
inevitably would be by the fender chain, could ram down the first, or
safety gate. But if it did, there would still be another set of gates
some 70 feet away. The chances here might be one in a hundred of the
second set being rammed down. From all this it will be seen that the
chances of the second pair of gates being rammed is so remote as to be
almost without the realm of possibility. But suppose all these
precautions should fail, and suddenly the way should be opened for the
water of Gatun Lake to rush through the locks at the destructive speed
of 20 miles an hour? Even that day has been provided against by the
construction of the big emergency dams. The emergency dams, like the
fender chains, are designed only for protection, and have no other use
in the operation of the locks. There will be six of these dams, one
across each of the head locks at Gatun, Pedro Miguel, and Miraflores.
These emergency dams will be mounted on pivots on the side walls of
the locks about 200 feet above the upper gates. When not in use they
will rest on the side wall and parallel with it. When in use they will
be swung across the locks, by electric machinery or by hand, and there
rigidly wedged in. It will require two minutes to get them in position
by electricity and 30 minutes by hand. There is a motor for driving
the wedges which will hold the dam securely in position, and limit
switches to prevent the dams being moved too far.
When a bridge is put into position across the lock, a series of wicket
girders which are attached to the upstream side of the floor of the
bridge are let down into the water, the connection between the bridge
and one end of each girder being made by an elbow joint. The other end
goes down into the water, its motion being controlled by a cable
attached some distance from the free end of the girder and paid out or
drawn in over an electrically operated drum. This free end passes down
until it engages a big iron casting embedded in the concrete of the
lock floor. This makes a sort of inclined railway at an angle of about
30 degrees from the perpendicular, over which huge steel plates are
let down into the water. There are six of these girders, and they are
all made of the finest nickel steel. When they are all in position, a
row of six plates are let down, and they make the stream going
through the locks several feet shallower. Then another row of plates
is let down on these, and the stream becomes that much shallower.
Another row of plates is added, and then another, until there is a
solid sheet of steel plates resting on the six girders, and they make
a complete steel dam which effectively arrests the mad impulse of the
water in Gatun Lake to rush down into the sea. The plates are moved up
and down by electrical machinery, and are mounted on roller-bearing
wheels, so that the tremendous friction caused by their being pressed
against the girders by the great force of the water may be overcome.
That the emergency dams will be effective is shown by the experience
at the "Soo" locks, on the canal connecting Lakes Superior and Huron.
There, a vessel operating under its own power, rammed a lock gate.
Although the emergency dam had grown so rusty by disuse that it could
be operated only by hand, it was swung across the lock and effectively
fulfilled its mission of checking the maddened flow of the water.
Another protective device for the locks is the big caisson gates that
will be floated across the head and tail bays when it is desired to
remove all the water from the locks for the purpose of permitting the
lower guard gates to be examined, cleaned, painted, or repaired, and
for allowing the sills of the emergency dams to be examined in the
dry. The caisson gates are 112-1/2 feet long, 36 feet beam, and have a
light draft of 32 feet and a heavy draft of 61 feet. When one is
floated into position to close the lock, water will be admitted to
make it sink to the proper depth. Then its large centrifugal pumps,
driven by electric motors, will pump the water out of the lock. When
the work on the lock is completed these pumps will pump the water out
of the caisson itself until it becomes buoyant enough to resume its
light draft, after which it will be floated away.
The machinery for opening and closing the lock gates called for
unusual care in its designing. The existing types of gate-operating
machinery were all studied, and it was found that none of them could
be depended on to prove satisfactory, so special machines had to be
designed.
A great wheel, resembling a drive wheel of a locomotive, except that a
little over half of the rim is cog-geared, is mounted in a horizontal
position on a big plate, planted firmly in the concrete of the wall
and bolted there with huge bolts 11 feet long and 2-1/4 inches in
diameter. This plate weighs over 13,000 pounds, and the wheel, cast in
two pieces, weighs 34,000 pounds. As the weight of the rim of the
wheel on the eight spokes probably would tax their strength too much
when the wheel is under stress, this is obviated by four bearing
wheels, perpendicular to the big wheel, which support the rim. Between
the crank pin and the point of attachment on the gate leaf there is a
long arm, or strut, designed to bear an operating strain of nearly a
hundred tons. The wheel will be revolved by a motor geared to the
cogged part of the rim.
An ingenious arrangement of electric switches is that used to protect
the gate-moving machines from harm. The big connecting rod between the
master wheel and the gate leaf is attached to the gate leaf by a nest
of springs capable of sustaining a pressure of 184,000 pounds, in
addition to the fixed pressure of 60,000 pounds. Should any
obstruction interfere with the closing of the gate and threaten a
dangerous pressure on the connecting rod, the springs, as soon as they
reach their full compression, establish an electrical contact and thus
stop the motor. Likewise, should any obstruction come against the gate
as the connecting rod is pulling it open, the springs again permit the
establishment of an electrical contact and stop the motor. All of
these precautions are entirely independent of and supplemental to the
limit switches, which cut off the power from the gate-moving machine
should the strain reach the danger line. These big machines move the
huge gate leaves without the slightest noise or vibration. Such a
machine is required for each of the 92 leaves used in the 46 gates
with which the locks are equipped. The operator can open or close one
of these big gates in two minutes.
[Illustration: ONE OF THE 92 GATE-LEAF MASTER WHEELS]
The control of the water in the culverts of the locks is taken care of
by an ingeniously designed series of valves. The big wall culverts, 18
feet in diameter, are divided into two sections at the points where
the valves are installed, by the construction of a perpendicular pier.
This makes two openings 8 by 18 feet. The big gates of steel are
placed in frames to close these openings just as a window sash is
placed in its frame. They are mounted on roller bearings, so as to
overcome the friction caused by the pressure of water against the
valve gates. They must be mounted so that there is not more than a
fourth of an inch play in any direction. The big wall culvert gates
will weigh about 10 tons each, and must be capable of operating under
a head of more than 60 feet of water. They will be raised and lowered
by electricity.
The electric locomotives which will be used to tow ships through the
locks are one of the interesting features of the equipment. There will
be 40 of them on the 3 sets of locks. The average ship will require
four of them, two at the bow and two at the stern, to draw it through
the locks. They will run on tracks on the lock walls, and will have
two sets of wheels. One set will be cogged, and will be used when the
locomotives are engaged in towing. The other set will be pressed into
service when they are running light. When a vessel is in one lock
waiting for the water to be equalized with that in the next one and
the gates opened to permit passage, the forward locomotives will run
free up the incline to the lock wall above, paying out hawser as they
go. When they get to the next higher level they are ready to exert
their maximum pull. Each locomotive consists of three parts: two
motors hitched together, and the tandem may be operated from either
end. The third part is a big winding drum around which the great
hawsers are wound. This towing windlass permits the line to be paid
out or pulled in and the distance between the ship and the locomotives
varied at will. The locomotive may thus exert its pull or relax it
while standing still on the track, a provision especially valuable in
bringing ships to rest. In the main, however, the pull of the
locomotive is exercised by its running on the semi-suppressed rack
track anchored in the coping of the lock walls. Each flight of locks
will be provided with two towing tracks, one on the side and one on
the center wall. Each wall will be equipped with a return track of
ordinary rails, so that when a set of locomotives has finished towing
a ship through the locks they can be switched over from these tracks
and hustled back for another job. When they reach the inclines from
one lock to the next above the rack track will be pressed into service
again until they reach the next level stretch.
Here again one meets the familiar safeguard against accident. Some
engineer of one of these towing locomotives might sometime overload
it, so the power of doing so has been taken out of his hands. On the
windlass or drum that holds the towing hawser there is a friction
coupling. If the engineer should attempt to overload his engine, or if
for any other reason there should suddenly come upon the locomotive a
greater strain than it could bear, or upon the track, or upon the
hawser, the friction clutch would let loose at its appointed tension
of 25,000 pounds, and all danger would be averted.
When the locomotives are towing a ship from the walls it is natural
that there should be a side pull on the hawser. This is overcome by
wheels that run against the side of the track and are mounted
horizontally. All of the towing tracks extend out on the approach
walls of the locks so that the locomotives can get out far enough to
take charge of a ship before it gets close enough to do the locks any
damage.
[Illustration: A _Mauretania_ IN THE LOCKS]
From the foregoing it will be seen that a great deal of electric
current will be required in the operation of the locks. This will be
generated at a big station at Gatun, with a smaller one at Miraflores,
and they will be connected. The overflow water will be used for
generating the required current, and in addition to the operation of
the lock machinery it will operate the spillway gates, furnish the
necessary lighting current, and eventually it may furnish the power
for an electrified Panama Railroad.
In passing a ship through the canal it will be necessary to open and
close 23 lock gates, of an aggregate weight of more than 25,000 tons,
to lower and raise 12 fender chains, each weighing 24,000 pounds, and
to shut and open dozens of great valves, each of which weighs tons.
All these operations at each set of locks will be controlled by one
man, at a central switchboard. In addition to these operations there
is the towing apparatus. The arrangement at Gatun is typical; there 4
fender chains must be operated, 6 pairs of miter gates, and 46 valves.
In all not less than 98 motors will be set in motion twice, and
sometimes this number may be increased to 143. Some of them are more
than half a mile away from the operator, and half of them are nearly a
quarter of a mile away.
The operator in his control house will be high enough to have an
uninterrupted view of the whole flight of locks over which he has
command. His control board will consist of a representation of the
locks his switches control. On his model he will see the rise and fall
of the fender chains as he operates them, the movement of the big lock
gates as they swing open or shut, the opening and closing of the
valves which regulate the water in the culverts, and the rise and fall
of the water in the locks.
A system of interlocked levers will prevent him from doing the wrong
thing in handling his switches. Before he can open the valves at one
end of a lock he must close those at the other end. Before he can
open the lock gates, the valves in the culverts must be set so that no
harm can result. Before he can start to open a lock gate, he must
first have released the miter-forcing machine that latches the gates.
Before he can close the gates protected by a fender chain, he must
first have thrown the switch to bring the fender chain back to its
protecting position, and he can not throw the switch to lower the
chain until he first has provided for the opening of the gate it
protects. All of this interlocking system makes it next to impossible
to err, and taking into consideration the additional safeguard of
limit switches, which automatically cut off the power when anything
goes wrong, it will be seen that the personal equation is all but
removed from the situation.