:Why does hot flowing hot water sound different than cold flowing
: water? When I start the water running in the shower before I undress,
: I can clearly hear when the hot water gets there.

The valve-heating-up explanation is likely part of the answer, but I have
heard the same phenomenon in partially open 1/4 turn ball valves which
don't close up significantly when temp increases.

Another possibility is related to how the noise is generated in the
first place: cavitation at the orifice. Under proper circumstances
when water pressure is released at the edges of a valve opening the
dynamics pull tiny transient near-vacuum bubbles which quickly
collapse with a shock. Add up the tiny "clicks" from these events
and you get the "hiss" of water escaping through a valve.

Note I said near-vacuum. The bubbles actually have a measure of
water vapor in them, according to the vapor pressure of water
at that temperature.

Now as water heats up, its vapor pressure increases. This changes
the absolute pressure of the cavitation bubbles, affecting their
size and energy, affecting the "clicks", affecting the integrated
sound.

A similar effect occurs with a metal teapot on the stove. As the
water heats up the sound changes as increasing vapor pressure of
the heating water changes the characteristics of the transient
bubbles on the kettle bottom which make the racket.

In a valve, the water is literally "boiling" in much the same
way.

Incidently, cavitation is violent enough on a microscopic level
to hammer tiny bits of the valve edges away, eventually
destroying the valve.

Bob (in an alternate life is a water plant operator) Miller

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On 2004-11-14 said:
writes: Hey, you know that trick! I
give my 17 year old hot water heater a pat each day while
flipping a load of wash. 17 years on a water heater! I'm impressed.
The ones I buy seem to have cracked the secret of the car battery
warranty. As soon as the warranty period is up, you can count on
them going within a couple of months.
HEy that anode rod that's supposed to do the electrolysis bit to save
the tank must actually work with the water you have. BAck where I
used to live you were lucky to get ten years on the tanks. THat
stuff was nasty. GO down to take a morning shower and see bright
orange liquid coming out of the shower head.




Richard Webb,
Electric SPider Productions, New Orleans, La.
REplace anything before the @ symbol with elspider for real email

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On 2004-11-14 said:
writes: Hey, you know that trick! I
give my 17 year old hot water heater a pat each day while
flipping a load of wash. 17 years on a water heater! I'm impressed.
The ones I buy seem to have cracked the secret of the car battery
warranty. As soon as the warranty period is up, you can count on
them going within a couple of months.
HEy that anode rod that's supposed to do the electrolysis bit to save
the tank must actually work with the water you have. BAck where I
used to live you were lucky to get ten years on the tanks. THat
stuff was nasty. GO down to take a morning shower and see bright
orange liquid coming out of the shower head.




Richard Webb,
Electric SPider Productions, New Orleans, La.
REplace anything before the @ symbol with elspider for real email

--

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On 2004-11-15 (ScottDorsey) said:
I wrote:
HEy that anode rod that's supposed to do the electrolysis bit to
save the tank must actually work with the water you have. BAck
where I used to live you were lucky to get ten years on the tanks.
THat stuff was nasty. GO down to take a morning shower and see
bright orange liquid coming out of the shower head.
And that is why you should do the monthly purge. Or at least every
six months. It's not that difficult to drain a gallon out of the
thing into a bucket.
You can buy heaters with a stainless steel lining, too, rather than
the cheap glass lining. They last a lot longer, but cost a lot
more. I just went from a well to city water and I'm seeing a lot
less crap coming out when I do the monthly purge, but I'm waiting
to see how that affects the total life.
tHose are better from what I've heard. THe community I lived in for a
number of years was on a municipal well and you'd even get bright
orange liquid coming from the cold water taps. ESpecially when they'd
purged the system with the fire hydrants in my neighborhood. THis was
a suburb and many were advocating we go back to hooking up to the
larger city's water system. THis stuff did serious damage to the
water meters the city installed oto btw.




Richard Webb,
Electric SPider Productions, New Orleans, La.
REplace anything before the @ symbol with elspider for real email

--



A good captain is one who is hoisting his first drink in a
bar when the storm hits.

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Date: Mon, 15 Nov 2004 19:36:44 GMT
Xref: number1.nntp.dca.giganews.com rec.audio.pro:1124840


On 2004-11-15 (ScottDorsey) said:
I wrote:
HEy that anode rod that's supposed to do the electrolysis bit to
save the tank must actually work with the water you have. BAck
where I used to live you were lucky to get ten years on the tanks.
THat stuff was nasty. GO down to take a morning shower and see
bright orange liquid coming out of the shower head.
And that is why you should do the monthly purge. Or at least every
six months. It's not that difficult to drain a gallon out of the
thing into a bucket.
You can buy heaters with a stainless steel lining, too, rather than
the cheap glass lining. They last a lot longer, but cost a lot
more. I just went from a well to city water and I'm seeing a lot
less crap coming out when I do the monthly purge, but I'm waiting
to see how that affects the total life.
tHose are better from what I've heard. THe community I lived in for a
number of years was on a municipal well and you'd even get bright
orange liquid coming from the cold water taps. ESpecially when they'd
purged the system with the fire hydrants in my neighborhood. THis was
a suburb and many were advocating we go back to hooking up to the
larger city's water system. THis stuff did serious damage to the
water meters the city installed oto btw.




Richard Webb,
Electric SPider Productions, New Orleans, La.
REplace anything before the @ symbol with elspider for real email

--



A good captain is one who is hoisting his first drink in a
bar when the storm hits.