Lock

Background

Locks have been used to fasten doors against thieves since earliest times. The Old Testament contains several references to locks, and the first archaeological evidence of locks are about 4,000 years old. These are Egyptian locks depicted in the pyramids. These earliest locks were of a type known as pin tumbler, and they are actually not very different from common door locks in use today. The Egyptian lock consisted of a heavy wooden housing mounted to the door. A wooden bolt passed through the lock and was held in place by iron pins which dropped into slots and held it firm. The key was a straight piece of wood with pegs projecting up from its end. When the key was inserted and pushed upwards, the pegs on the key lifted the pins in the lock, and the bolt was freed.

The Greeks developed a simple door lock by about 700 b.c. This used a latchstring to pull a bolt through brackets in the door. By pulling the string, the homeowner could lock the door from the outside. Then, the string was stuffed back through the keyhole. The key itself was a sickle-shaped piece of metal from two to three feet long. The key could be fitted into the hole in the lock to pull back the bolt from the outside. The major drawback to this lock was that anyone with a curved stick or their own key could open it. And, the large metal key was cumbersome.

Romans adopted the Greek lock system, but solved the problem of the heavy key by chaining it to a slave, and then chaining the slave to the doorpost. Eventually, Romans developed a new kind of lock, called the warded lock. In the warded lock, notches and grooves called wards were cut into the keyhole, and the key was cut with corresponding notches and grooves. Only the proper key could fit into the keyhole, and then its tip engaged the bolt and withdrew it. The warded lock was much smaller than its predecessor, and keys were small enough that no slave was needed to take care of it. But because the classic Roman toga had no pockets, the key still wasn't easy to carry, and so it was usually attached to a finger ring. Warded locks were widespread in Europe by the thirteenth century and remained in use well into the eighteenth century. They persisted in spite of the fact that they were easy to pick, and were barely an obstacle to determined thieves.

The Romans also used padlocks, in which a key turned a bolt releasing a spring on a shackle. These were used for locking trunks. Similar locks were invented in China, India and Russia during the same era. The Chinese also invented the combination lock. It had moveable rings inscribed with numbers or letters, and its hasp was released only when the rings were aligned in the proper sequence of symbols. Combination locks found their way to Europe, and were used in the Middle Ages especially on couriers' dispatch boxes.

European locksmiths in the Middle Ages made beautiful, intricate locks which took appallingly long hours of work to build and offered little real security. Locksmiths apprenticed for 10 years to reach the journeyman level. To reach the rank of master, the locksmith had to complete a masterpiece lock for approval by his guild. These masterpieces took thousands of hours to complete, and the results were generally much more decorative than functional. Locks that offered improved protection against theft were not developed until the late eighteenth century, when an English locksmith, Robert Barron, patented what was known as the double-action lever-tumbler lock in 1788. Barron's lock had two interior levers held by a spring. These levers, or tumblers, had notches that hooked over the bolt and held it shut. The key also had notches on it corresponding to the notches on the levers. When the right key was inserted, it would lift both tumblers, and the bolt could be drawn. Other inventors added many more tumblers to this design, and it proved much more difficult to pick than the earlier warded locks.

Linus Yale Jr., an American locksmith born in 1821, made a significant improvement in lock design in 1861 with his invention of the modern pin-tumbler lock. The design principal was similar to the Egyptian lock. This lock has a rotating cylinder which is held fast in the bolt by a series of five spring-driven pins of different heights. The key has five notches on it that correspond to the heights of the five pins. When the correct key is inserted, the pins line up level, and the cylinder can be turned to disengage the bolt. If the wrong key is inserted, the pins catch. Picking a Yale lock proved extremely difficult, and the parts for the lock could be inexpensively mass-produced by machine. Within several years of its invention, the Yale lock became the standard, replacing virtually all earlier lock technology.

Even more sophisticated locks were developed in the twentieth century, including timer locks used in bank vaults, push button locks, and electronic locks that operate with a credit card like key. The manufacturing process that follows is for a standard pin-tumbler lock. This is the kind of lock that may be found on any front door or file cabinet drawer.

Raw Materials

Standard five-tumbler key locks are made of various strong metals. The internal mechanisms of locks are generally made of brass or die-cast zinc. The cam, which is the tongue that protrudes from the lock to secure it, is usually made of steel or stainless steel. The outer casing of a lock may be made of brass, chrome, steel, nickel or any other durable metal or alloy.

The Manufacturing
Process

Design

• 1 Locks come in grades, from low-security to high-security. A low-security lock is generally made from cheaper materials, and its parts can be mass-produced. A company that manufactures low-security locks may have two or three available models, and keep in stock the parts needed to customize them. Beyond low-security, the lock manufacturer is generally what is called an original equipment manufacturer, meaning that they make the parts for their locks as well as the final products. This kind of manufacturer may keep only the most basic and common parts in stock, and most of its orders require custom design.

  The process begins with the manufacturer assessing the customer's specifications. The customer orders a lock to fit a certain size door for example, and asks that the locks can be opened with a master key. The lock manufacturer then comes up with the best design for that customer's needs. In some cases, a customer may have purchased locks in the past from one company, and now wants more identical locks from a different manufacturer, who promises to make them more economically. Then, the lock manufacturer examines the customer's original locks and goes through what is known as a reverse engineering process. The manufacturer's design team figures out from the existing lock how to make their product match it. In many cases, the customer's first lock company has patented aspects of its lock construction. The second manufacturer may not duplicate it without infringing the other company's patents. So, the designers "design around" the first company's product, producing a lock that will match the customer's originals and serve the same purpose, but using different mechanisms. Medium and high security locks in most cases go through this design stage, making the production of locks a time-consuming process. A reputable manufacturer making anything but low security locks may take from eight to 12 weeks to produce locks for an order, from the time the specifications are given to when the locks are packed and shipped.

The key

• 2 For the standard five-tumbler key lock, the key is made first. The lock manufacturer buys key blanks and cuts the ridges, or combinations, in each key. Each key has five bumps on it that are cut to different levels. These levels are designated by numbers. A low cut is one, next up is two, then three. In many cases, there are only four levels, though some manufacturers may use as many as seven. A five-tumbler key lock with four levels in the key yields four to the fifth power, or 1024, different possible combinations of ridges in the key. The five ridges are listed by the height of each level, yielding what is called the combination for the key. A key with the combination 12341 is cut with the first ridge at level one, the second at two, the next at three, and so on. The lock manufacturer chooses the combinations from a random list and cuts each key differently.

Internal mechanisms

• 3 The internal mechanisms are made next. These have been designed to fit this particular lock order, and the machinery that makes them may have to be re-tooled or reset. Because the tiny interior parts, specifically the pins, must be manufactured to exceedingly fine tolerances, the machinists may make a trial run before starting a big job. Then the machines may be re-set if necessary. The machining of small brass parts takes many steps. They may be cast, then grooved, ridged, jeweled, and polished. Precision tools handle these jobs, cutting the metal to within tolerances of plus or minus 0.001 of an inch.

Other parts

• 4 The manufacturer also makes the other parts of the lock. The cylinder, or plug, that the key fits into, guard plates, washers, the bolt or cam, and the casing, are all made according to design specifications, by die-casting and then further machining. The number of parts varies with the design of the lock, but even a small and relatively simple lock may have thirty separate parts, and some of these parts require multiple toolings. The process of making the lock components can take several weeks.

Assembly

• 5 When all the parts are ready, the locks are assembled by hand. Lock workers sit at well-lit tables with a kit of the pieces of the lock in a bin, and the key on a stand in front of them. An experienced worker can tell the combination of the key just by looking at it. The worker first fills the plug, or cylinder, of the lock with the pins that correspond to the combination of the key. The worker inserts a tiny spring and then the lock pin, using a small tool called an assembly pick to hold the small parts. The assembly pick has a small screwdriver on one end and a point on the other, and the worker uses it to prod the delicate parts in where they belong. Once the plug is filled according to the key combination, the worker snaps or screws together the other parts around the lock. Though it is skilled work, it takes no special training, and these workers are not locksmiths.

Final steps

• 6 Once a lock is fully assembled, the worker checks it with the key to make sure it works. It may pass to a quality control station at this point, and then be dusted or polished. Workers package the completed locks and box them for shipment.

Quality Control

The most important aspect of quality control in lock manufacturing is ensuring that the tiny machined parts are the exact sizes specified. For a new custom order, the machinists usually produce trial samples of the parts, and each one of these may be inspected and measured manually, using precise gauges. If all seems to be going well, the machinists will run the rest of the order, and then perhaps one of every 500 or 1,000 parts is checked. After the worker assembles the lock, he or she tests it with the key to make sure it works properly. A quality control specialist may also spot check the locks at this stage.

The Future

Many entities such as universities and large corporate headquarters that use large numbers of locks are converting to electronic pass-key systems. These use a magnetic swipe card to open a door. The cards can have a bar code on them, and computers can be used to store information on who goes in through each door, raising privacy issues for some concerned people. Other high-tech locks open with voice activation or palm or fingerprint recognition. Such locks offer relatively high security, but are generally too expensive and elaborate for the ordinary citizen's home. However, the trend towards these kinds of electronic and computer-controlled locks is growing in the late 1990s, and they will undoubtedly be more prevalent in the future.

Where to Learn More

Books

Roper, C.A. The Complete Book of Locks and Locksmithing. Blue Ridge Summit, Pennsylvania: Tab Books, 1991.

Tchudi, Stephen. Lock and Key. New York: Scribner's, 1993.

Periodicals

Belsie, Laurent. "Slide Toward Surveillance Society: New Technology Allows Government and Corporations to Cut Fraud and Boost Security, but Privacy Concerns Mount." Christian Science Monitor. (March 4, 1999).

Leigh, Bobbie. "An Alarming Trend: Bulletproof Living." Wall Street Journal. (November 29, 1996).

—AngelaWoodward

Lock

History

Construction and operation

Resources

A lock or water lock is an enclosed, rectangular chamber with gates at each end, within which water is raised or lowered to allow boats or ships to overcome differences in water level. Locks have been used over 2,000 years, and although they are most often used by boats on canals, they also are used to transport massive ships between seas. All locks operate on the simple buoyancy principle that any vessel, no matter what size, will float atop a large enough volume of water. By raising or lowering the level of a body of water, the vessel itself goes up or down accordingly. Locks are used to connect two bodies of water that are at different ground levels as well as to “walk” a vessel up or down a river’s more turbulent parts. This is done by a series of connecting or “staircase” locks. Locks contributed significantly to the Industrial Revolution by making possible the interconnection of canals and rivers, thus broadening commerce. They still play a major role in industrial society.

History

The ancestor of the modern lock is the flash lock, also called a navigation weir or stanch. It originated in China and is believed to have been used as early as 50 BC. The flash lock was a navigable gap in a masonry dam or weir that could be opened or closed by a single wooden gate. Opening the gate or sluice very quickly would release a sudden surge of water that was supposed to assist a vessel downstream through shallow water—often a very dangerous process. Using the flash lock to go upstream was usually safe, but extremely slow since the gap in the dam was used to winch or drag a vessel through.

At some point, what now seems a very obvious improvement was made, and a second gate was added to the flash lock, thus giving birth to the pound lock. The first known example of a pound lock (whose dual gates “impound” or capture the water) is in China in AD 984. Supposedly built by Chiao Wei-Yo on the West River section of the Grand Canal near Huai-yin, it consisted of two flash locks about 250 feet (76.2 m) apart. By raising or lowering guillotine gates at each end, water was captured or released. The space between the two gates thus acted as an equalizing chamber that elevated or lowered a vessel to meet the next water level. This new method was entirely controllable and had none of the hazards or surges of the old flash lock.

Although a primitive form of lock was used in Belgium as early as 1180, the first pound lock in Europe was built at Vreeswijk, Holland, in 1373. Like its Chinese ancestor, it also had guillotine/up-and-down gates. The pound lock system spread quickly throughout Europe during the next century and was eventually replaced by an improved system that formed the basis of the modern lock system. During the fifteenth century, the multitalented Italian artist Leonardo da Vinci (1452-1519) served the Duke of Milan as engineer and devised an improved form of pound lock whose gates formed a V-shape when closed. In 1487, da Vinci built six locks with gates of this type. These gates turned on hinges, like doors, and when closed they formed a V shape pointing upstream— thus giving them their name of miter gates. Da Vinci realized that one great advantage of miter gates is that they were self-sealing by the water pressure (since they point upstream). Also when there is a difference in water level between one side and the other, the pressure holding the gates together is at its greatest.

Most of the great canals of Europe use locks. In France, the Briare Canal, completed in 1642, included forty locks, one series of which was a staircase of six locks that handled a fall of 65 feet (20 m). The famous Canal du Midi that leads to the Mediterranean was finished in 1692 and used 26 locks to surmount the 206-foot (61 m) difference from Garonne to Toulouse. It then descended 620 feet (189 m) through 74 locks. The first lock in England was built in 1566, but it was not until 1783 that a lock was completed in North America at Lake St. Francis in Canada.

Construction and operation

The earliest locks were built entirely of wood, with stone and then brick eventually becoming standard materials. The gates themselves were always wooden, with some lasting as long as 50 years. Filling or emptying these early locks was often accomplished by hand-operated sluices built in the gates. On later and larger locks, conduits or culverts built into the lock wall itself were not only more efficient, but let the water enter in a smoother, more controlled manner.

Nearly all locks operate in the following manner: (1) A vessel going downstream to shallower water enters a lock with the front gate closed. (2) The rear gate is then closed and the water level in the lock is lowered by opening a valve. The vessel goes down as the water escapes. (3) When the water level inside the lock is as low as that downstream, the front gate is opened and the vessel continues on its way. To go upstream, the process is reversed, with the water level being raised inside the lock. What the operators always strive for is to fill or empty the lock in the fastest time possible with a minimum of turbulence.

In modern locks, concrete and steel have replaced wood and brick, and hydraulic power or electricity is used to open and close the gates and side sluices. Movable gates are the most important part of a lock, and they must be strong enough to withstand the water pressure arising from the often great difference in water levels. They are mostly a variation of da Vinci’s miter gates, except now they usually are designed to be stored inside the lock’s wall recesses.

Probably the best known locks in the world are those used in the Panama Canal—the most-used canal in the world. Completed in 1914, the Panama Canal is an interoceanic waterway 51 miles (82 km) long that connects the Atlantic and Pacific Oceans through the Isthmus of Panama. It has three major sets of locks, each of which is built in tandem to allow vessels to move in either direction, like a separated, two-way street. Each lock gate has two leaves, 65 feet (20 m) wide by 7 feet (2 m) thick, set on hinges. The gates range in height from 47-82 feet (14-25 m), and are powered by large motors built in the lock walls. The chambers are 1,000 feet (305 m) long, 110 feet (33.6 m) wide, and 41 feet (12.5 m) deep. Most large vessels are towed through the locks. As with all modern locks, they are operated from a control tower and use visual signals and radio communications. Any future major changes or improvements in the canal or its locks must consider the fact that ocean-going vessels are simply becoming too large to pass through. The future may see the construction of a sea-level canal 10 miles (16 km) west of the existing canal. If so, it, like the Suez Canal, will contain no locks of any kind.

KEY TERMS

Flash lock —A simple wooden gate that was placed across a moving body of water to hold it back until it had become deep; the sudden withdrawal of which would cause a “flash” of water downstream that would carry a boat over the shallows below.

Guillotine gate —An early wooden gate on a lock that was operated by being raised or lowered.

Miter gate —An improved type of lock gate that turns on hinges, like a door, and meets to form a vee pointing upstream.

Pound lock —A name for an early form of two-gate lock in which a chamber is enclosed at either end by vertically-rising gates and into which water is admitted or released to change its water level and allow a vessel to do the same.

Staircase lock —Two or more locks sharing a common gate that form a series of water steps and allow a vessel to negotiate a steep rise.

Resources

BOOKS

Paget-Tomlinson, Edward. The Illustrated History of Canal & River Navigations. Sheffield, England: Sheffield Academic Press, 1993.

OTHER

Rideau Canal Waterway (Ontario, Canada). “History of the Rideau Lockstations: The Basics of a Rideau Lock” <http://www.rideau-info.com/canal/history/locks/lock-basics.html> (accessed December 2, 2006).

Leonard C. Bruno

lock¹ / läk/ • n. 1. a mechanism for keeping a door, lid, etc., fastened, typically operated only by a key of a particular form: the key turned firmly in the lock. ∎  a similar device used to prevent the operation or movement of a vehicle or other machine: a bicycle lock. ∎  (in wrestling and martial arts) a hold that prevents an opponent from moving a limb. ∎  [in sing.] archaic a number of interlocked or jammed items: a street closed by a lock of carriages.2. a short confined section of a canal or other waterway in which the water level can be changed by the use of gates and sluices, used for raising and lowering vessels between two gates. ∎  an airlock.3. (a lock) inf. a person or thing that is certain to succeed; a certainty.4. archaic a mechanism for exploding the charge of a gun. • v. 1. [tr.] fasten or secure (something) with a lock: she closed and locked her desk | [as adj.] (locked) behind locked doors. ∎  (lock something up) shut and secure something, esp. a building, by fastening its doors with locks: the diplomatic personnel locked up their building and walked off | [intr.] you could lock up for me when you leave. ∎  enclose or shut in by locking or fastening a door, lid, etc.: the prisoners are locked up overnight Phil locked away the takings every night. ∎  (lock someone up/away) imprison someone. ∎  (lock something up/away) invest money in something so that it is not easily accessible: vast sums of money locked up in pension funds. ∎  (lock someone down) confine prisoners to their cells, esp. so as to gain control. ∎  [intr.] (of a door, window, box, etc.) become or be able to be secured through activation of a lock: the door will automatically lock behind you.2. make or become rigidly fixed or immovable: [tr.] he locked his hands behind her neck | [intr.] their gaze locked for several long moments. ∎  (lock someone/something in) engage or entangle in (an embrace or struggle): they were locked in a legal battle. ∎  trap or fix firmly or irrevocably. this may tend to lock in many traders with their present holdings. ∎  (lock someone/something into) cause to become caught or involved in: they were now locked into the system. ∎  (of land, hills, ice, etc.) enclose; surround: the vessel was locked in ice.3. [intr.] go through a lock on a canal: we locked through at Moore Haven.PHRASES: have a lock on inf. have an unbreakable hold on or total control over.lock horns engage in conflict.lock, stock, and barrel including everything; completely: the place is owned lock, stock, and barrel by an oil company.under lock and key securely locked up.PHRASAL VERBS: lock onto locate (a target) by radar or similar means and then track.lock someone out1. keep someone out of a room or building by locking the door.2. (of an employer) subject employees to a lockout.lock someone out of exclude someone from: those now locked out of the job market.DERIVATIVES: lock·a·ble adj.lock·less adj.lock² • n. a piece of a person's hair that coils or hangs together: she pushed back a lock of hair. ∎  (locks) chiefly poetic/lit. a person's hair: flowing locks and a long white beard. ∎  a tuft of wool or cotton. ∎  (locks) short for dreadlocks.DERIVATIVES: locked adj. his curly-locked comrades.

Lock

A lock or water lock is an enclosed, rectangular chamber with gates at each end, within which water is raised or lowered to allow boats or ships to overcome differences in water level. Locks have a history of over 2,000 years, and although they are most often used by boats on canals, they also are used to transport massive ships between seas. All locks operate on the simple buoyancy principle that any vessel, no matter what size, will float atop a large enough volume of water. By raising or


lowering the level of a body of water, the vessel itself goes up or down accordingly. Locks are used to connect two bodies of water that are at different ground levels as well as to "walk" a vessel up or down a river's more turbulent parts. This is done by a series of connecting or "staircase" locks. Locks contributed significantly to the Industrial Revolution by making possible the interconnection of canals and rivers , thus broadening commerce. They still play a major role in today's industrial society.

History

The ancestor of the modern lock is the flash lock, also called a navigation weir or stanch. It originated in China and is believed to have been used as early as 50 b.c. The flash lock was a navigable gap in a masonry dam or weir that could be opened or closed by a single wooden gate. Opening the gate or sluice very quickly would release a sudden surge of water that was supposed to assist a vessel downstream through shallow water. This was often very dangerous. Using the flash lock to go upstream was usually safe but extremely slow since the gap in the dam was used to winch or drag a vessel through.

At some point, what now seems to be a very obvious improvement was made, and a second gate was added to the flash lock, thus giving birth to the pound lock. The first known example of a pound lock (whose dual gates "impound" or capture the water) is in China in 984 a.d. Supposedly built by Chiao Wei-Yo on the West River section of the Grand Canal near Huai-yin, it consisted of two flash locks about 250 ft (76.2 m) apart. By raising or lowering guillotine gates at each end, water was captured or released. The space between the two gates thus acted as an equalizing chamber that elevated or lowered a vessel to meet the next water level. This new method was entirely controllable and had none of the hazards and surges of the old flash lock.

Although a primitive form of lock was used in Belgium as early as 1180, the first pound lock in Europe was built at Vreeswijk, Holland in 1373. Like its Chinese ancestor, it also had guillotine or up-and-down gates. The pound lock system spread quickly throughout Europe during the next century and was eventually replaced by an improved system that formed the basis of the modern lock system. During the fifteenth century, the multi-talented Italian artist, Leonardo da Vinci (1452-1519), served the Duke of Milan as engineer and devised an improved form of pound lock whose gates formed a V-shape when closed. In 1487, da Vinci built six locks with gates of this type. These gates turned on hinges, like doors, and when closed they formed a vee shape pointing upstream-thus giving them their name of miter gates. Da Vinci realized that one great advantage of miter gates is that they were self-sealing by the pressure of the water (since they point upstream). Also when there is a difference in water level between one side and the other, the pressure holding the gates together is at its greatest. Most of the great canals of Europe use locks. In France, the Briare Canal, completed in 1642, included 40 locks, one series of which was a staircase of six locks that handled a fall of 65 ft (20 m). The famous Canal du Midi that leads to the Mediterranean was finished in 1692 and used 26 locks to surmount the 206-ft (61 m) difference from Garonne to Toulouse. It then descended 620 ft (189 m) through 74 locks. The first lock in England was built in 1566, but it was not until 1783 that a lock was completed in North America at Lake St. Francis in Canada.

Construction and operation

The earliest locks were built entirely of wood , with stone and then brick becoming standard materials. The gates themselves were always wooden, with some lasting as long as 50 years. Filling or emptying these early locks was often accomplished by hand-operated sluices built in the gates. On later and larger locks, it was found that conduits or culverts built into the lock wall itself were not only more efficient but let the water enter in a smoother, more controlled manner. Nearly all locks operate in the following manner: (1) A vessel going downstream to shallower water enters a lock with the front gate closed. (2) The rear gate is then closed and the water level in the lock is lowered by opening a valve. The vessel goes down as the water escapes. (3) When the water level inside the lock is as low as that downstream, the front gate is opened and the vessel continues on its way. To go upstream, the process is reversed, with the water level being raised inside the lock. What the operators always strive for is to fill or empty the lock in the fastest time possible with a minimum of turbulence . In modern locks, concrete and steel have replaced wood and brick, and hydraulic power or electricity is used to open and close the gates and side sluices. Movable gates are the most important part of a lock, and they must be strong enough to withstand the water pressure arising from the often great difference in water levels. They are mostly a variation of da Vinci's miter gates, except now they usually are designed to be stored inside the lock's wall recesses.

Probably the best known locks in the world are those used in the Panama Canal—the most-used canal in the world. Completed in 1914, the Panama Canal is an interoceanic waterway 51 mi (82 km) long that connects the Atlantic and Pacific Oceans through the Isthmus of Panama. It has three major sets of locks, each of which is built in tandem to allow vessels to move in either direction, like a separated, two-way street. Each lock gate has two leaves, 65 ft (20 m) wide by 7 ft (2 m) thick, set on hinges. The gates range in height from 47-82 ft (14-25 m), and are powered by large motors built in the lock walls. The chambers are 1,000 ft (305 m) long, 110 ft (33.6 m) wide, and 41 ft (12.5 m) deep. Most large vessels are towed through the locks. As with all locks today, they are operated from a control tower and use visual signals and radio communications. Any future major changes or improvements in the canal or its locks must consider the fact that ocean-going vessels are simply becoming too large to pass through. The future may see the construction of a sea-level canal 10 mi (16 km) west of the existing canal. If so, it, like the Suez Canal, will contain no locks of any kind.

Resources

books

De Bono, Edward. Eureka! An Illustrated History of Inventions From the Wheel to the Computer. London: Thames and Hudson, 1974.

Paget-Tomlinson, Edward. The Illustrated History of Canal & River Navigations. Sheffield, England: Sheffield Academic Press, 1993.

Leonard C. Bruno

KEY TERMS

Flash lock

—A simple wooden gate that was placed across a moving body of water to hold it back until it had become deep; the sudden withdrawal of which would cause a "flash" of water downstream that would carry a boat over the shallows below.

Guillotine gate

—An early wooden gate on a lock that was operated by being raised or lowered.

Miter gate

—An improved type of lock gate that turns on hinges, like a door, and meets to form a vee pointing upstream.

Pound lock

—A name for an early form of two-gate lock in which a chamber is enclosed at either end by vertically-rising gates and into which water is admitted or released to change its water level and allow a vessel to do the same.

Staircase lock

—Two or more locks sharing a common gate that form a series of water steps and allow a vessel to negotiate a steep rise.

Lock

A lock or water lock is an enclosed, rectangular chamber with gates at each end, within which water is raised or lowered to allow boats or ships to overcome differences in water level. Locks have a history of over 2,000 years, and although they are most often used by boats on canals, they also are used to transport massive ships between seas.

All locks operate on the simple buoyancy principle that any vessel, no matter what size, will float atop a large enough volume of water. By raising or lowering the level of a body of water, the vessel itself goes up or down accordingly. Locks are used to connect two bodies of water that are at different ground levels as well as to "walk" a vessel up or down a river's more turbulent parts. This is done by a series of connecting or "stair-case" locks. Locks contributed significantly to the Industrial Revolution (period beginning about the middle of the eighteenth century during which humans began to use steam engines as a major source of power) by making possible the interconnection of canals and rivers, thus broadening commerce. They still play a major role in today's industrial society.

History

The ancestor of the modern lock is the flash lock. It originated in China and is believed to have been used as early as 50 b.c. The flash lock was a navigable gap in a masonry dam that could be opened or closed by a single wooden gate. Opening the gate very quickly would release a sudden surge of water that was supposed to assist a vessel downstream through shallow water. This was often very dangerous. Using the flash lock to go upstream was usually safe but extremely slow since the gap in the dam was used to winch or drag a vessel through.

At some future date, a second gate was added to the flash lock, thus giving birth to the pound lock. The first known example of a pound lock (whose dual gates "impound" or capture the water) was in China in a.d. 984. It consisted of two flash locks about 250 feet (76 meters) apart. By raising or lowering guillotine or up-and-down gates at each end, water was captured or released. The space between the two gates thus acted as an equalizing chamber that elevated or lowered a vessel to meet the next water level. This new method was entirely controllable and had none of the hazards and surges of the old flash lock.

The first pound lock in Europe was built at Vreeswijk, the Netherlands, in 1373. Like its Chinese ancestor, it also had guillotine gates. The pound lock system spread quickly throughout Europe during the next century, but was eventually replaced by an improved system that formed the basis of the modern lock system. During the fifteenth century, Italian artist and scientist Leonardo da Vinci (1452–1519) devised an improved form of pound lock whose gates formed a V-shape when closed. In 1487, Leonardo built six locks with gates of this type. These gates turned on hinges, like doors, and when closed they formed a V-shape pointing upstream—thus giving them their name of miter gates. One great advantage of miter gates was that they were self-sealing from the pressure of the upsteam water.

Construction and operation

The earliest locks were built entirely of wood, with stone and then brick becoming standard materials. The gates themselves were always wooden, with some lasting as long as 50 years. Filling or emptying these early locks was often accomplished by hand-operated sluices or floodgates built in the gates. On later and larger locks, it was found that conduits or culverts built into the lock wall itself were not only more efficient but let the water enter in a smoother, more controlled manner. Nearly all locks operate in the following manner: (1) A vessel going downstream to shallower water enters a lock with the front gate closed. (2) The rear gate is then closed and the water level in the lock is lowered by opening a valve. The vessel goes down as the water escapes. (3) When the water level inside the lock is as low as that downstream, the front gate is opened and the vessel continues on its way. To go upstream, the process is reversed, with the water level being raised inside the lock. What the operators always strive for is to fill or empty the lock in the fastest time possible with a minimum of turbulence.

In modern locks, concrete and steel have replaced wood and brick, and hydraulic power or electricity is used to open and close the gates and side sluices. Movable gates are the most important part of a lock, and they must be strong enough to withstand the water pressure arising from the often great difference in water levels. They are mostly a variation of Leonardo's miter gates, except now they usually are designed to be stored inside the lock's wall recesses.

Probably the best known locks in the world are those used in the Panama Canal—the most-used canal in the world. Completed in 1914, the Panama Canal is an interoceanic waterway 51 miles (82 kilometers) long that connects the Atlantic and Pacific Oceans through the Isthmus of Panama. It has three major sets of locks, each of which is built in tandem to allow vessels to move in either direction, like a separated, twoway street. Each lock gate has two leaves, 65 feet (20 meters) wide by 7 feet (2 meter) thick, set on hinges. The gates range in height from 47 to 82 feet (14 to 25 meters) and are powered by large motors built in the lock walls. The chambers are 1,000 feet (305 meters) long, 110 feet (34 meters) wide, and 41 feet (13 meters) deep. Most large vessels are towed through the locks. As with all locks today, they are operated from a control tower using visual signals and radio communications.

[See also Canal ]