Lock Gates.—The lock gates, each composed of two leaves, are 65 ft. wide, from 47 ft. 4 in. to 82 ft. high, 7 ft. thick, and weigh from 390 to 73o tons. Each is a huge webbed steel box, the girders of which are covered with a steel sheathing. All por tions of the interior are accessible, with watertight compartments providing for the adjustment of the buoyancy so as to control within limits the dead load on the bearings, making the leaf practically float in the water. This watertight compartment is subdivided vertically into three sections, each independently watertight, so that if the shell should be broken or leak, probably only one section would be affected. An air shaft, 26 in. in diam eter, runs from the bottom compartment up to the top of the gate, and is also watertight where it passes through the upper half of the leaf.
The girders are made with manholes through the webs, provid ing communication from the top to the bottom of the leaf, and are connected by several sets of vertical transverse diaphragms of solid plates, running from top to bottom of the leaf, thus making a cellular construction, and dividing the spaces between the horizontal girders into small pockets, all of which are ac cessible through manholes. Each leaf rests at the bottom of its heel post upon a hemispherical pivot of forged nickel steel, and is hinged at the top to the masonry of the lock wall. It swings free on the pivot like a door, without wheels or other support beneath it. Intermediate gates are used in all except one pair of locks, and divide the space into two chambers, one 600 and the other 400 ft. in length. This makes possible a saving of water and time in locking small vessels through, for 95% of the vessels navigating the high seas are less than 600 ft. in length. The highest gates and the highest lock walls on the canal are those of the lower locks at Miraflores, and these locks are the only ones which have no intermediate gates. The depth of water on the mitre sills is 4o feet.
The locks are filled and emptied through the large and smaller culverts. The large culverts are controlled at points near the gates by large valves, and each of the small culverts feeds in both directions through the laterals, thus permitting the passage of water from one twin lock to another, effecting a saving of water if desired. The average time required to fill or empty a lock chamber is 8 min. if both centre and side wall culverts are used, and 12 min. if only one culvert is used. The average time to pass a vessel through the three flights at Gatun locks is an hour, from arrival to clearance ; for the one lift at Pedro Miguel half an hour, and for the two flights at Miraflores three-quarters of an hour.
The time of passage of a vessel from one terminal port of the canal to the other is 7 hours.
Before a lock can be entered, a fender chain, stretched across the walls of the approach, must be passed. If all is proceeding properly, this chain is dropped into its groove at the bottom of the channel. If by any chance the ship is moving too rapidly for safety, the chain remains stretched and the vessel runs against it. The chain, which is operated by hydraulic machinery in the walls, then pays out slowly by automatic release until the vessel is brought to a stop. If the vessel should get away from the towing locomotive and, breaking through the chain, ram the first gate, there is a second gate 5o ft. away, protecting the lock, which arrests further advance. When the leaves of this gate swing open, the vessel is towed in, and the gate is closed behind it.
Then, from 105 openings placed at regular intervals in the lock floor, water pours in, lifting the vessel to the level of the lock above.
The gates are opened and closed by a powerful machine in vented by Edward Schildhauer, an electrical engineer in the employ of the Isthmian Canal Commission. It consists of a crank gear or wheel moving through an arc of 197°, placed horizontally in the lock wall. To the outer rim of the wheel is attached a strut or connecting rod which is fastened to the top of a lock gate 17 ft. from the pintle or hinge. When the wheel turns in either direction the gate leaf is opened or shut, the operation taking two minutes. The crank gear, constructed of cast steel, is 19 ft. 2 in. in diameter and weighs approximately 35,000 pounds. It is connected with an electric motor, and a small electric switch sets it in motion. Every operation in the passage of a vessel through the lock, except the movements of the towing locomotives, is controlled by one man in a building at the top of the centre wall commanding an unobstructed view of every part of the locks.