why does the shower lose pressure when you set the water to a warmer temperature?
In: Physics
My understanding of this, is that the hot water valve closes a little because of thermal expansion when you increase the hot water flow. Of course it does depends on the valves set up.
The water flows through a boiler and gets heated first before it gets to the tap. This process decreases the throughput of water to the tap whenever it needs to get heated first
Showers set the temperature by mixing the (usually fairly cold) tap water and the hot water from the heater. When you’re at a middle temperature, both of those flows are running full blast, and forcing their way through your shower head. When you turn it all the way up, you just have the hot water flow, but the same shower head. Less flow through the same nozzle = less pressure.
The hot water probably comes from a storage cylinder, usually located only a little way above the height of the shower. The water pressure out of the cylinder is therefore pretty low, meaning a slower flow rate.
The cold water is either supplied by the main inbound pipes at a much higher pressure or from a tank, often placed higher than the hot water tank (as water often flows from the cold water tank down to fill the hot water cylinder). Both of these result in higher pressure cold water so a higher flow. You can test this by turning on hot water and then cold water from a basin tap. It should behave the same as the shower.
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