The Story of the Locks
The great locks at Panama through which ships are
lifted up from the sea to Gatun Lake and back down to the sea again, after a
thirty-seven-mile sail through fresh water, constitute a vast and wonderful engineering
work. Their total cost approximates $60,000,000. With their approach walls,
their aggregate length is nearly two miles. There are three steps on each side of
the isthmus by which ships are lifted up 85 feet on the one side and let down 85 feet on
the other Each of these steps has two lock chambers, making parallel shipways
through the locks. The side walls vary from 45 to 50 feet wide at the floor of the
locks, and at a point 24 1/3 feet above the floor they begin to step in 6-foot steps until
they are 8 feet wide at the top. The total width of the locks between the two side
walls is 280 feet In the middle of the locks, and running parallel with the side
walls, is a center wall, which divides the locks into two chambers this wall is 60
feet wide all the way up. At a point 42 1/2 feet above the floor of the lock the
solid construction ceases, and a U-shaped opening runs the entire length of the wall
This serves to provide three long tunnels, the full length of the center wall, one above
the other. The lowest of these tunnels is used for drainage purposes; the middle one
is used for the conduits through which the electric cables are run; the upper tunnel is
used as a passageway from one piece of operating machinery to another.
Running lengthwise through the side and center walls are three large water tunnels, or culverts, eighteen feet in diameter -- large enough to accommodate a modern passenger train. These huge culverts are used to carry the water down from the lake into the several locks. From these tunnels extend a series of cross culverts which pass under the floor of the locks. There are fourteen of these cross culverts in each lock chamber. Seven of them open from the side culvert and seven from the center wall culvert. These cross culverts are large enough for the passage of a two-horse team. Through each one of them there are five openings into the floor of the lock chamber itself, making seventy in all in the bottom of each lock chamber. These holes are so large that a sugar barrel could pass through each one without difficulty. The passage of water through the culverts is controlled by a large number of valves. In the large wall culverts, these valves consist of two huge gates, each 8 by 18 feet, which slide up and down in frames after the manner of a window. Each of these gates weighs ten tons, and must be able to hold in check a head of sixty feet of water. The gates which control the passage of the water from the wall culverts to the cross culverts have ordinary cylindrical valves. They are so arranged that each one may be opened or closed independently, or they may be opened or closed in series.
The gates which separate the several chambers of a flight of locks are of enormous size, ranging from 47 to 82 feet high, and are 7 feet thick. They are built in two leaves to each gate, each of these leaves being 65 feet wide. The weight of the leaves varies from 390 tons to 730 tons, depending upon the height of the leaf. They are swung to the walls of the lock chamber in such a way that when they are closed they extend across the lock in the shape of a flattened V, with the apex pointing in the direction from which the pressure comes. The lower sill of each gate leaf weighs approximately eighteen tons. The gates are built up of structural steel, and are covered with large riveted steel plates, just as the hull of a ship is covered. Each of these gate leaves is hung on huge pintles anchored to the walls of the lock. The hinges that are hung on them weigh 36,752 pounds each. They were made to stand a strain of 40,000 pounds before stretching, and 70,000 pounds before breaking. Under an actual test it was found that they were able to stand a strain of 3,300,000 pounds before breaking.
The movement of a gate leaf is accomplished through a huge connecting rod, one end of which is attached to the leaf about midway between the wall and the other end of the leaf; the other end is attached to a huge master wheel which lies flat on the top of the lock wall. This master wheel weighs 34,000 pounds and turns on a huge center pin which is keyed in a heavy casting, anchored securely to the concrete. The casting and the center pin weigh 13,000 pounds. The rim of the great master wheel is so heavy that its weight would break the spokes, and so it is supported in four places by rollers. One-half of this rim is cog geared. Through these it is revolved by an electric motor which drives a train of gears and pinions. These turn the rim of the wheel, which moves the connecting rod to the gate, causing the gate to pen or close in two minutes. the action is just the reverse of the action of the connecting rod on the driving wheel of a locomotive. If the reader can picture a locomotive suspended in the air, and the driving wheel moved by power applied to the rim, the resulting movement of the connecting rod with the piston will represent in general outline the method by which the gate leaves are moved back and forth. The motor is remotely controlled by an operator stationed in the controlling house near the lower end of the upper locks, a simple pull of a small switch being sufficient either to close or open a 700-ton gate.
Elaborate precautions have been taken against
accidents to the gate leaves. It is easy to see that this huge connecting rod,
driven by the powerful master wheel, pushing the gate shut or pulling it open, would cause
great damage in case the gate struck an obstruction, unless some method were devised to
stop the machinery automatically. Such a method was devised and is in
operation. At the gate end of the connecting rod there are two large nests of
springs, one of which comes into play when the gate is being opened, and the other when
the gate is being closed. These springs will bear a pressure of 60,000 pounds before
compressing in the slightest degree, and a pressure of 134,000 pounds before
breaking. In case a gate leaf is being closed, and a serious obstruction is
encountered, one nest of springs will be compressed. when they reach a certain
degree of compression a lever is automatically thrown which cuts off the electric power
from the master wheel and stops it instantly. The opposite nest of springs acts in
the same way when the gate strikes an obstruction on being opened.
The connecting rods and master wheels are so arranged that the greatest power is exerted when the most of it is needed. As a gate leaf is swung open it must force out the water in the V-shaped space between it and the lock wall, so that most power is needed just at that time. When a gate swings back against its recess in the wall the angle of the connecting rod is such as to give it great leverage but slow motion. The same wise provision has been made for holding the gate in position when closed. At this point the connecting rod is practically on a dead center, so that any pressure that may be exerted on it does not tend to revolve the master wheel.
It may be imagined that without many sealing devices there would be openings between the gate leaves and between the gates, walls, and floors that would leave them anything but water tight. One of the devices in se is known as a miter-forcing machine. This consists of a mechanism placed on the end of one gate leaf, which reaches out and takes hold of an engaging part on the end of the opposite leaf, when the gates are in the act of closing. It forces the two leaves together and holds them in rigid contact so long as the gates are shut. In opening the gates it is necessary first to release this miter-forcing machine. On the floor of the lock is placed a heavy timber which comes in contact with very heavy rubber flaps four inches wide, on the bottom of the gate, thus making a perfect seal.
Around no other canal locks in the world have so many safeguards been thrown. In the first place, across the locks ahead of each gate, a huge chain, whose links are fashioned out of three-inch iron, is swung in such a way that any ship not stopping in due time will ram its nose into the chain and will be checked by it before any damage can be done. This chain will stop within 70 feet a 10,000-ton ship moving at the rate of five knots an hour. Each of these protective chains has a great hydraulic paying-out arrangement at either end, which is imbedded in the lock walls. The chain begins to pay out when the pressure reaches 100 tons. It will not break under a pressure of less than 262 tons. Each chain is 428 feet long, and its two ends are attached to big plungers in cylinders imbedded in the lock walls. There is a broad surface of water under each plunger from which small valves open up when a pressure of 750 pounds to the square inch is brought against them. The harder the pressure, the greater the amount of water let out and the grater the resulting speed of the paying-out apparatus. The chain pays out four feet for each foot of movement of the piston. The hydraulic arrangement of the chains practically makes them vast water buffers against the progress of the ship. The paying-out process is rapid enough to prevent any undue strain on the fender chains, and yet slow enough to stop the ship before it can do any harm. There are twenty-four of these fender chains across the locks, and their normal position is one of readiness to stop any ship which approaches the lock gates when it is not under thorough control. These chains are raised and lowered in about one minute. As there is always danger that a paying-out mechanism may be flooded, a unique automatic pump has been installed. A flood valve is in position always ready to turn on an electric switch, which starts the pump the minute the paying-out mechanism is threatened with such an overflow of water. As soon as the water is pumped out, the switch is turned back by the same automatic process, and the pump stopped.
It has been demonstrated that the majority of accidents in the operation of locks are caused by ships passing through them under their own power. A single misunderstood order or a single moment of hesitation in executing an order passed from the lock operator to the man in the engine room may result in disastrous consequences, and has so resulted upon many occasions in various locks. At Panama no ship will be allowed to pass through the locks under its own power. All vessels are required to come up to the guide walls, where they are taken in tow by electric towing engines. There are engines on each of the two walls of a lock chamber, and with ordinary ships two of thee will be connected with the forward part of the ship by cables, while two other engines get behind to hold the vessel from moving too fast. In this way the average ship will have four engines attached to it by long cables, two for pulling it forward and two for preventing it from moving too fast, and they stop it exactly when a stop is desired. Each of these engines is provided with a windlass by which it may control a ship even when standing still. There are two tracks for these engines. The track used in towing a ship through the locks is a rack track to which the engine is geared. An ordinary railroad track is used for the towing locomotives when they run idle. These towing locomotives were built by the General Electric Company. The ones designed by the Canal Commission provided friction drums which would automatically permit the cable to pay out. It was found that these friction drums were unreliable, and they were discarded. Another trouble encountered with the first engine built was that the paying-out drum was too narrow, which caused the cable much injury in its operation. Still another difficulty was the are caused by the uneven surface of the jar caused by the uneven surface of the rack track, when the wheels which protected the locomotive from a side pull engaged it. This trouble was overcome by utilizing huge springs in a side-thrust-preventing mechanism. The solenoid brakes and friction clutches were substituted for hand brakes and clutches, and the windlass was made wider, so that the engine, as finally built, embodies the most approved ideas in towing locomotive design.
Another method of protecting the locks from injury is the provision of extra gates at every exposed position. These gates are seventy feet away from the operating gates. Should a ship, approaching the locks, by any change break the big fender chain which is intended to stop it, the safety gates would next be rammed. These gates are even more securely mounted than the main operating gates, and the apex of the two leaves is turned in the direction from which the ship would come. It would take tremendous force to ram down a pair of these protective gates. Every precaution will be taken to stop ships before they reach the fender chains, and it is to be doubted whether one in a thousand would ram its nose into these chains. Likewise, it is to be doubted whether one in a thousand of those which did encounter the fender chains would break them, so that there is not one chance in a million that the protective gates will be rammed. And it is probably a thousand to one that no ship which had negotiated these defenses would break down the protective gates. Thus the possibility of ramming the operating gates is seen to be exceedingly remote.
But in their unprecedented spirit of precaution the designers of the locks have provided against even so remote a chance as that. At the head of each set of locks they have built an emergency dam with which they may close up the lock chambers with sheets of steel, in the even that all other precautions fail. These dams are huge cantilever pivot bridges, one of which is built on each side wall of a set of locks. When out of use the dam reposes on the wall, parallel with its longitudinal axis. when needed to close the channel it is swung across the lock by electricity. To the floor beams of the end of the bridge which goes across the lock, there are attached a series of six wicket girders.
One end of each of these girders is free, and by steel cables they may be raised or lowered singly or in series. when it is desired to use the dam, the bridge is swung across the channel, and the free end of the girders let down to the bottom of the lock, where they engage in an offset. These thus make a sort of inclined railway, down which huge steel plates are run on live roller bearings. There are six plates resting on each girder, and when they are all in position they make a solid steel dam extending from the bottom of the locks to the floor of the bridge. Every precaution has been taken to make these dams efficient. The bridges are swung by electricity, and limit switches make certain that they will stop in exactly the right position. Electrically operated machinery drives the wedges which hold the bridge firmly in position. The emergency dams were made by the American Bridge Company, and each one had to be thoroughly tried out before it was accepted. It takes only a few minutes to swing the bridge across the channel, and not much longer to close up the channel with the steel-plated dam which swings down from the floor of the bridge to the floor of the locks. While all of the machinery of the emergency dams is operated by electricity, provision is made for their operation by hand in the even that they are needed in an emergency when no electric current is available. that these dams give efficient results is shown by experience at the Soo Canal. there a ship rammed the gates and started the waters flowing through the locks with destructive force. The emergency dam had been so long out of use that it could be operated only by hand. Yet with this difficulty, the Soo lock operators were able to check the flow of water in a very little while.
Every precaution has been taken to eliminate the personal equation in the operation of the locks at Panama. The man who operates a set of locks occupies a control house on the center wall of the upper flight of locks, thus giving him an unobstructed view of the whole series of locks with which he must deal. Further than this, he has a little model of the locks and every result of his manipulation of the levers and switches stands out before him on the model in his office. When he opens the mighty gates of the locks, he also opens the gates of the little lock model; when he operates the valves in the water supply culverts, he also operates the valves of his little model. In this way he is able at all times to know exactly what he has been ding. Further than this, he cannot make a wrong movement even if he should be careless. His system of levers and buttons is an interlocking one, and he simply cannot do the wrong thing. For instance, he cannot let the water through the large culverts until the gates which are to control this water have first been set into position. Likewise, he cannot operate the gates until he has first set the fender chains in their proper position. In this way practically every chance of accident from carelessness is eliminated.
Having seen now what the locks are, let us return and look at them in the process of construction. In building them enough concrete was used to build a row of houses reaching from Chicago to St. Louis. Upward of five million barrels were used in constructing the locks, spillways, and dams. The stone for the locks on the Atlantic side was brought from Porto Bello; that used on the Pacific side was quarried at Ancon Hill. Two different types of material handling machines were used. On the Atlantic side the concrete was handled by huge Lidgerwood cableways. The towers of these cableways were 85 feet high, and they were set on the banks of the canal so that the cableways would span the set of locks. The cables consisted of two and a half inch lock steel wire. They were guaranteed to carry six tons at a trip and to make twenty trips an hour. Each cableway was guaranteed for a life of 60,000 trips.
A circular electric railroad connected the storage piles of sand, stone, and cement with the concrete mixing machinery. The material in the storage piles had been brought to Gatun in barges, the sand from Nombre de Dios,the stone from Porto Bello, and the cement from the docks at Colon. The sand and stone supply was unloaded upon the storage piles by cableways like those used in handling the concrete in building the locks. It was taken from these piles and loaded upon the little cars of the circular railway, in exactly the right proportions. Then the cars were sent on their way to the concrete mixers, which could deliver a mixed charge or receive an unmixed one without stopping. The little cars on the circular railway ran without motormen. They had automatic governors that held them to a constant speed up hill and down, and when going down hill their motors were reversed into generators, thus making them furnish, in part, the current that lifted some other car over the incline.
After the concrete mixers and finished rolling around the stone, sand, cement, and water in their busy maws, they dumped the mixture out in big buckets mounted on little electric trains operated by a motorman on a third rail track. Each little train carried two buckets. One of them would pull up to the concrete mixers, receive its two bucketfuls of concrete, nearly six tons of it to the bucket, and then hasten away to a point under a Lidgerwood cableway. Here would come down out of the air two empty buckets, which would be set on the cars beside the two full ones. A little wig-wagging, and the full buckets were caught up into the air to the steel cableway where they struck a carrier that carried them across to the desired position over the locks. Here they were emptied and returned to be delivered to the net train that came along, in exchange for two other buckets filled with concrete.
On the Pacific side cranes were used in lieu of cableways, and dinkey steam locomotives instead of electric railways. One crane carried the materials to the concrete mixers, which turned over the concrete mixers, which turned over the concrete to the little trains, just as at Gatun. They conveyed it to the other crane, which lifted it up to the desired position, where it was dumped.
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from: The History of the
by Ira E. Bennett, 1915
March 25, 1999