How does the water that comes out of our sink and shower faucets change temperature when we move the handle(s) back and forth? How does it know to go from hot to cold and visa versa?


How does the water that comes out of our sink and shower faucets change temperature when we move the handle(s) back and forth? How does it know to go from hot to cold and visa versa?

In: Engineering

There is a hot and cold water feed that comes into the faucet. The handle moves a valve that changes how much of the hot and cold gets mixed into the stream of water that comes out of the tap.

If the handle is all the way to one side only hot water will come out, if it’s all the way to the other side, only cold water will come out. Somewhere in between it will mix the two together.

Hot water has a different source for you water which is the hot water heater.

When you turn the knobs on the faucet you are adjusting the volume of cold versus hot water that you use. That in turn is why you can control the temperature.

The faucets just mix hot and cold water together, the amount of each is based on how far each lever is turned. If hot is all the way on and cold is all the way on you’ll have warm water. If you slide the cold handle to off the temp will increase. Vice Versa

The handles act as controls for a valve that mixes water that comes from two different places. Water comes into your house in a Main Line. That main line sends water to the cold water points all through out your home like sinks, showers, and garden hoses. It also sends water to a hot water heater which then heats the water to approximately 120°F. Once hot, the water heater has a secondary line out, feeding heated water to all of the hot water points in the sinks, showers/tubs, and typically a washing machine. At the sink faucet, when you turn the handle, you adjust how much hot water you’re letting through and how much cold. They then mix into a single point and come out of the faucet at the resulting mixed temperature.

[This is a water heater](×1024.jpg), it takes in a large tank of water and heats it up with either gas flame or electrical heater coils. You’ll have one somewhere in the basement.

In your house, you have [hot pipes and cold pipes]( bringing hot water (from the heater) and cold water (straight from the city supply) to your faucets and sinks. [Under your sink]( you’ll see hot water and cold water connected to the faucets.

[The faucet]( just combines the hot and the cold, more hot or more cold, depending on how you adjust the knobs. The knobs simply let more (hot or cold) water through when you twist them.

Think of your mixer tap like a set of scales.

If one tap is opened further than the other, the water will be tempered towards that end heat wise.

Hot tap fully open and cold tap only half open = water roughly 75% as hot as your boiler could make it.

Both taps fully open = water roughly 50% as hot as boiler can make it.

These are examples only and are purely for the purpose of explaining the process (because cold water has a varied effect on hot water in various quatities)

it’s like the ice cream machine that lets you get vanilla or chocolate ice cream but there’s also the middle handle that lets you get both. Except that instead of only three handles the knobs let you go from all chocolate and no vanilla to all vanilla and no chocolate and everywhere between the two ends. Except replace chocolate with cold water and vanilla with hot water.

Underneath each handle, there is a valve with an opening and a gasket. Normally, the gasket blocks water from coming through. As you turn the handle, the valve slides around, exposing the opening to the supply water. Water flow depends on how much of the opening is exposed, that is how you go from a trickle by turning a little, to full blast by turning all the way.

By modulating the hot and cold valves, you can mix water to virtually any degree between the temp of your incoming cold water, and the highest setting on your water heater.