I've always wondered about this....
When I turn on the hot water, cold water comes out at first, then the hot water gets to the faucet after a bit. When the hot water arrives, the faucet makes a different sound!
Why is this?
Me too. I notice this on the valve for the bathtub (which is one of those anti scalding valves).
I have noticed this all my life, a half century before anti-scalding valves became popular. I was told many years ago it was simply expansion in the valve from the hot water that changed the flow characteristics. I suppose YMMV with different valve designs but if you listen carefully you can hear it in most of them, particularly if the "cold" water is really cold.
The cold is right there but the hot has to come from the heater and the travel time is what you are noticing.
Hot water is less dense and experiences a different turbulence (and sound) as it passes through the valve mechanism.
And, as the water de-pressurizes gases come out of solution and form new bubbles.
Water holds more dissolved gases when cold, but the gases stay in solution in the water heater because of the pressure. The water gets to the valve, the pressure goes down dramatically, and the gases come out of solution.
This is the same mechanism that causes bubbles to form at the bottom of a pot of water on the stove long before its boiling.
Dave
True, Dave ... thanks for the addition.
Gee I just learned stuff about something I never even thought about:-))
Lou
Hot water moves much faster than cold water. It's similar to blowing through a tube; blow harder and the sound changes.
Take a plastic jug and put a small hole near the bottom. Fill it with hot water and note the stream. Do the same with cold water. It is amazing to see the difference. You can record the time it takes to empty for comparison. There is more (kinetic) energy in the warmer water.
I am going to try that:-))
Lou
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