Editing Lock (water navigation) (section)

==Basic construction and operation==
[[File:Canal lock.svg|thumb|upright=1.5|A plan and side view of a generic, empty canal lock. A lock chamber separated from the rest of the canal by an upper pair and a lower pair of mitre [[floodgate|gates]]. The gates in each pair close against each other at an 18° angle to approximate an arch against the water pressure on the "upstream" side of the gates when the water level on the "downstream" side is lower.]]
{| style="border: 1px solid #999;"
|+ '''Principle of operation of a pound lock'''
!colspan="2"|For a boat going upstream:
|rowspan="6"|[[File:Pound lock sequence.svg|224px]]
!colspan="2"|For a boat going downstream:
|-
|valign="top" align="right" nowrap|1–2.
|valign="top"|The boat enters the lock.
|valign="top" align="right" nowrap|8–9.
|valign="top"|The boat enters the lock.
|-
|valign="top" align="right" nowrap|3.
|valign="top"|The lower gates are closed.
|valign="top" align="right" nowrap|10.
|valign="top"|The upper gates are closed.
|-
|valign="top" align="right" nowrap|4–5.
|valign="top"|The lock is filled with water from upstream.
|valign="top" align="right" nowrap|11–12.
|valign="top"|The lock is emptied by draining its water downstream.
|-
|valign="top" align="right" nowrap|6.
|valign="top"|The upper gates are opened.
|valign="top" align="right" nowrap|13.
|valign="top"|The lower gates are opened.
|-
|valign="top" align="right" nowrap|7.
|valign="top"|The boat exits the lock.
|valign="top" align="right" nowrap|14.
|valign="top"|The boat exits the lock.
|}
All pound locks have three elements:
* A watertight ''chamber'' connecting the upper and lower canals, and large enough to enclose one or more boats. The position of the chamber is fixed, but its water level can vary.
* A ''gate'' (often a pair of "pointing" half-gates) at each end of the chamber. A gate is opened to allow a boat to enter or leave the chamber; when closed, the gate is watertight.
* A set of ''lock gear'' to empty or fill the chamber as required. This is usually a simple valve (traditionally, a flat panel (paddle) lifted by manually winding a rack and pinion mechanism) which allows water to drain into or out of the chamber.{{sfn |Cumberlidge |2009 |p=23}} Larger locks may use pumps.<ref>{{cite web |url=https://www.abcboathire.com/more-information/a-guide-to-operating-locks |archive-url=https://web.archive.org/web/20230602022656/https://www.abcboathire.com/more-information/a-guide-to-operating-locks |archive-date=2 June 2023 |url-status=live |title=How do canal locks work? |publisher=ABC Boat Hire}}</ref>

The principle of operating a lock is simple. For instance, if a boat travelling downstream finds the lock already full of water:
* The entrance gates are opened and the boat moves in.
* The entrance gates are closed.
* A valve is opened, this lowers the boat by draining water from the chamber.
* The exit gates are opened and the boat moves out.{{sfn |Cumberlidge |2009 |p=23}}

If the lock were empty, the boat would have had to wait 5 to 10 minutes while the lock was filled. For a boat travelling upstream, the process is reversed; the boat enters the empty lock, and then the chamber is filled by opening a valve that allows water to enter the chamber from the upper level. The whole operation will usually take between 10 and 20 minutes, depending on the size of the lock and whether the water in the lock was originally set at the boat's level.{{sfn |Cumberlidge |2009 |p=23}}

Boaters approaching a lock are usually pleased to meet another boat coming towards them, because this boat will have just exited the lock on their level and therefore set the lock in their favour – saving about 5 to 10 minutes. However, this is not true for staircase locks, where it is quicker for boats to go through in convoy, and it also uses less water.<ref>{{cite web |url=https://www.droitwichcanals.co.uk/page24.html |archive-url=https://web.archive.org/web/20220104083714/https://www.droitwichcanals.co.uk/page24.html |archive-date=4 January 2022 |url-status=live |title=Staircase Canal Locks |publisher=Droitwich Canals}}</ref>

[[File:Canal-sequence.jpg|thumb|left|700px|<u>Operation of a canal lock</u><br/>
1–3. Boat enters 'empty' lock<br/>
4. Bottom gates are closed, bottom paddles closed, top paddles opened, lock starts to fill<br/>
5. Lock is filling with water, lifting boat to the higher level]]
{{Clear}}