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A canal lock or '''navigation lock''' is a device that lifts or lowers boats, barges or other vessels from one water level to another. Locks used on Canal s allow the negotiation of hills without recourse to lengthy detours, or the use of Tunnel s or Aqueduct s. The same kind of locks are used on River s, often in connection with Dam s (such as mill weirs), since there is generally a difference in water level between the upstream side of a dam and the downstream side. A lock traditionally consists of two pairs of Oak or Elm gates placed one after the other along a navigable channel of water. Modern commercial locks consist of large steel gates but use essentially the same swinging gate design, with the exception of some low head locks that use sliding gates (see Kiel Canal ). Another alternative is the Guillotine Lock , which uses a vertically moving steel gate - these are quite common on parts of the UK Canal System in East Anglia . The system operates in much the same way as an Airlock but acts between two levels of water as opposed to two levels of air pressure. OPERATION usually close at an 18° angle to approximate an arch against the weight of the water.]] A s built into the canal bank, which when opened allow water to pass through Culvert s and into the lock. Some locks will not have ground paddles and, in such cases, paddles on the top gates are used. Modern locks use pipes and valves to fill the locks but most are still filled by gravity alone. Once the lock is full, the top gates are opened, and the boat enters the lock. The gates are then closed again, and the paddles on the bottom gates are opened, letting the water drain from the lock to the lower water-level. The bottom gates are then opened, and the boat continues on its way. The two halves of a lock gate meet at a Chevron which points against the flow of the water. This prevents the lock gates from bursting open from the differences in Pressure between an empty lock and the full force of canal above it. It also has the effect of sealing the lock whenever the water levels at each side of the gate are different. On some English narrow canals (i.e. those with locks approximately 7 feet / 2.1m wide), a single gate the full width of the lock is used instead of a pair of gates. This was cheaper to construct and quicker to operate (as only one gate needs to be opened). A single gate is predominant on the upper end of narrow locks in England , but does occur at the lower end on some canals, notably most locks on the Birmingham Canal Navigations . However, using a single gate for the lower end of the lock means a very heavy gate as the lower gate is taller than the upper gate, and means the lock has to be longer to accommodate the opening of the wider gate while a boat is in the lock. Pictures below depict various lock operations: |
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