When looking at a traditional
English pub, a strong identifying feature is the set of wooden levers on the bar, used to pull
pints of
beer. These are called hand pumps.
A hand pump was originally called a beer engine, a patent device from the beginning of the 20th Century. The lever connects to a piston shaft, so that when the lever is pulled, liquid is drawn from a cylinder, which traditionally holds half a pint (hence one pull = 1/2 pint). A non return valve prevents air from entering while the lever is pushed back to its vertical position.
Sadly, hand pumps are disappearing from British pubs, owing to the greed of the pubcos, and their lack of interest in promoting real ale (there are exceptions to this, such as Wetherspoons).