How does a water faucet/tap work? The ones with both hot and cold water in 1 tap (looking at you, England).
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There are hot and cold water tubes going to it. The handle has two jobs, the mixture of hot/cold and the total volume passing through. For example left/right can be opening the outlet to the hot/cold inlet respectively. Any setting in between results in a mixture of certain parts. Up/down simply opens the outlet and thus controls the volume let through.
Just a valve assembly. It’s kind of different for each faucet, but rotating from hot to cold gradually closes the hot valve and opens the cold valve. Then the hot and cold water are allowed to mix before they come out.
The reason England normally has them separate stems from old laws that sought to prevent contamination between the hot and cold water lines. The hot water was not deemed safe to drink at the time. I don’t think it’s legally required anymore, but it remains that way out of tradition.
A mixer tap have two valves in it, one for hot and one for cold water which end up in the same pipe going to the tap. You either adjust each separately or there are mechanics within the tap to allow you to set the mixture and flow rate instead. There are various ways this can be done mechanically. There are also mixer taps with a small ceramic/bimetallic element which will change shape depending on temperature and this can be used to adjust the mixture. You then set the temperature and let the tap adjust the mixture to be just right. These are common in showers and bathtubs.
For England specifically the mixer tap have only recently been legal. There are a few explanations of why, either through early adoption of plumbing in London and sanitary regulations coming later or in order to lower cost of constructing building after the blitz. However hot water in England have not had the same requirements for cleanliness as most other parts of the world. So not only was hot water not drinkable but you could not even mix hot and cold water at any point due to the risk of bacteria being carried into the cold water system infecting it. Therefore you could not have a mixer tap and needed two taps, one for hot and one for cold. The water could then be mixed in the sink or washbowl so you could wash yourself with it. And even though mixer taps are now allowed, at least where the plumbing have been upgraded to modern standards, people are still used to adjusting each valve separately like the old taps. This is slowly changing though and more modern installations comes with the mechanics for setting the mixture and flow rate independently. It is even not that unheard of to find temperature controlled showers either.
All of what you see on the outside is to control what is essentially a tube with holes in it. When you turn it “on”, you are pushing this pipe in to where the holes in it meet the water pipes. When you push it side to side to adjust the temperature, you are rotating the holes away from one pipe and toward the other, making the water hotter and colder.
Thats how it is in the US as well. Inside the tap are two valves that dump into the main water outlet.
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