The Panama Canal. Frederic J. Haskin
train engines which passed back and forth hard by. The cranes would take their filled buckets and leave empty ones in exchange, and this was kept up day in and day out until the locks were completed. When the plant was removed from Pedro Miguel to Miraflores, a large part of the concrete was handled directly from the mixers to the walls by the cranes without the intermediary locomotive service.
The cost of the construction of the locks was estimated in 1908 at upward of $57,000,000. But economy in the handling of the material and efficiency on the part of the lock builders cut the actual cost far below that figure. On the Atlantic side about a dollar was saved on every yard of concrete laid—about $2,000,000. On the Pacific side more than twice as much was saved.
Before the locks could be built it became necessary to excavate down to bed rock. This required the removal of nearly 5,000,000 cubic yards of material at Gatun. Then extensive tests were made to make certain that the floor of the locks could be anchored safely to the rock. These tests demonstrated that by using the old steel rails that were left on the Isthmus by the French, the concrete and rock could be tied together so firmly as to defy the ravages of water and time. A huge apron of concrete was built out into Gatun Lake from the upper locks at that place, effectively preventing any water from getting between the rocks and the concrete lying upon them.
CHAPTER V
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