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?
On 22 Feb 2007 10:50:22 -0800, email@example.com wrote:
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
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.
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
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