We're testing a new copper line for leaks.

The line was purged of air, filled with water at 116 psi, and monitored
with a pressure gauge.

After first night, pressure dropped to 102 psi.

After second night, pressure dropped to 92 psi.

This leads me to believe that there's a leak, however, there are no
signs of humidity whatsoever.

Is it possible for a line that shows no humidity (i.e. a line that
presumably has no leaks) to keep loosing pressure?

Is there a logical explanation for this?

Thanks in advance.

renux wrote:

We're testing a new copper line for leaks.

The line was purged of air, filled with water at 116 psi, and monitored
with a pressure gauge.

After first night, pressure dropped to 102 psi.

After second night, pressure dropped to 92 psi.

This leads me to believe that there's a leak, however, there are no
signs of humidity whatsoever.

Is it possible for a line that shows no humidity (i.e. a line that
presumably has no leaks) to keep loosing pressure?

Is there a logical explanation for this?

Thanks in advance.

Has the temperature changed?

Might the joints (if any) be creeping?

Have you calculated the change in volume that would be needed to account
for what you're seeing? Water's not terribly compressible.

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

water cooled off and pressure dropped.
heat water pipe and pressure will rise.
or gauge problem.

It's possible for the leak to evaporate without condensing on the pipe,
especially in low humidity.

"renux" wrote in message
oups.com...
We're testing a new copper line for leaks.

The line was purged of air, filled with water at 116 psi, and monitored
with a pressure gauge.

After first night, pressure dropped to 102 psi.

After second night, pressure dropped to 92 psi.

This leads me to believe that there's a leak, however, there are no
signs of humidity whatsoever.

Is it possible for a line that shows no humidity (i.e. a line that
presumably has no leaks) to keep loosing pressure?

Is there a logical explanation for this?

Thanks in advance.

assuming it was filled with cool water you have a leak somewhere. can
you examine the entire line? is it exposed?

116 psi!!! Where did you get WATER at that presure? I always thought
leaks were tested with air presure. Water is not compresible, and
changes in temperature will change the presure, I think. --Phil

renux wrote:

We're testing a new copper line for leaks.

The line was purged of air, filled with water at 116 psi, and monitored
with a pressure gauge.

After first night, pressure dropped to 102 psi.

After second night, pressure dropped to 92 psi.

This leads me to believe that there's a leak, however, there are no
signs of humidity whatsoever.

Is it possible for a line that shows no humidity (i.e. a line that
presumably has no leaks) to keep loosing pressure?

Is there a logical explanation for this?

Thanks in advance.


--
Phil Munro Dept of Electrical & Computer Engin
Youngstown State University
Youngstown, Ohio 44555

Has the temperature changed?

Yes, there has was a variation of about 20oF.


Might the joints (if any) be creeping?

It's hard to say since most of the line is not exposed.


Have you calculated the change in volume that would be needed to account
for what you're seeing? Water's not terribly compressible.

I haven't, but this morning we refilled the line and purpuosefully
opened the faucet to experience a similar drop in preassure. The water
lost was about a third of a mug.

We are actually testing 3 lines in this fashion: 1 cooper line for
water and 2 copper lines for gas.

The good news is that the line for water has stabilized at 76 psi for
the last 72 hrs. so I feel pretty comfortable with this.

For the gas lines I'll start another thread.

Thanks!

Most of the line is not exposed. However, the line stabilized to 76 psi
for the last 72 hrs., so it seems to be ok. Thanks!

It's been a while so I may not be completely correct but here goes: Water
is compressible and that is the crux of why pressure can change in a fixed
volume system such as the copper lines. Water, like almost any fluid,
contains air in solution (entrained air) and it is this air that gets
compressed (or expands).
Take the expression:
Delta P=(Delta V)/V*BM
where Delta P=change in pressure; Delta V =change in volume; V=Volume under
pressure (copper lines); BM=Bulk Modules
As the temperature of the fluid changes so does its density (lbs/cubic ft).
Since there is no change in the weight of the fluid it's volume will change
via compression/expansion of the entrained air.
The temperature (density) does not change enough to account for a pressure
change of approx 20% (116 to 92) so look for a leak somewhere.
As a side note: the compressibility of water (or any fluid, like hydraulic
oil) plays a significant role in high response control systems. Too much
entrained air and the end result is poor response and in many cases an
unstable system.
MLD



"Phil Munro" wrote in message
...
116 psi!!! Where did you get WATER at that presure? I always thought
leaks were tested with air presure. Water is not compresible, and
changes in temperature will change the presure, I think. --Phil

renux wrote:

We're testing a new copper line for leaks.

The line was purged of air, filled with water at 116 psi, and monitored
with a pressure gauge.

After first night, pressure dropped to 102 psi.

After second night, pressure dropped to 92 psi.

This leads me to believe that there's a leak, however, there are no
signs of humidity whatsoever.

Is it possible for a line that shows no humidity (i.e. a line that
presumably has no leaks) to keep loosing pressure?

Is there a logical explanation for this?

Thanks in advance.


--
Phil Munro Dept of Electrical & Computer Engin
Youngstown State University
Youngstown, Ohio 44555

We used a home-made pump that uses a hydraulic component and a lever.
We used water because it makes it very easy to spot a leak. Thanks!

You should cap off these lines and not have any faucets attached, then
pressure test them with air.

"renux" wrote in message
ups.com...

Has the temperature changed?

Yes, there has was a variation of about 20oF.


Might the joints (if any) be creeping?

It's hard to say since most of the line is not exposed.


Have you calculated the change in volume that would be needed to account
for what you're seeing? Water's not terribly compressible.

I haven't, but this morning we refilled the line and purpuosefully
opened the faucet to experience a similar drop in preassure. The water
lost was about a third of a mug.

We are actually testing 3 lines in this fashion: 1 cooper line for
water and 2 copper lines for gas.

The good news is that the line for water has stabilized at 76 psi for
the last 72 hrs. so I feel pretty comfortable with this.

For the gas lines I'll start another thread.

Thanks!

On Fri, 20 Jan 2006 09:22:53 -0500, Phil Munro
wrote:

116 psi!!! Where did you get WATER at that presure? I always thought
leaks were tested with air presure. Water is not compresible, and
changes in temperature will change the presure, I think. --Phil

Again, no experience, and I thought I would learn about this here.
Some people here seem to have written as if using water is the normal
procedure, but others hint that it's not, or say to use air.

I offer this for the OP's consideration.
Water is only compressible to a slight degree, and the major thing
they could be compressing is the slight amount of air that may be left
in the pipes when they are is filled with water. Because that volume
is small, tThat means that it would only take the loss of a little bit
of air or a little bit of water (giving more room for the air), to
multiply the available space significantly and make the pressure drop
significantly.

Also, the air can get absorbed intio the water. This happens much
faster at high pressures, and iiuc when the air is absorbed in the
water, it takes up no space (amazingly) and thus the pressure would
drop.

Look at the water prssure arrangements in 6-story buildings. (In nyc.
There may be a different height where this applies in other places.)
I think the same thing applies with houses that have wells and
compression tanks.

Four or 5 stories and less, city water pressure is enough, Seven or 9
stories or more, they put a water tank on the roof.

At 6 stories they pump the water into a tank that is about 1/3 air
after the air in the tank is compressed, and they use the air pressure
to pump the water to the sixth floor (and the other floors, but for
the sixth it's essential) After a while the air in the compression
tank has been absorbed into the water, the pressure drops, and a
separate air pump has to be used to add more air. Here the water is
being replaced with new water every time someone uses any water,
unlike the OP's sealed pipe, but there is still absorption to the
extent the original water will take it.

renux wrote:

We're testing a new copper line for leaks.

The line was purged of air, filled with water at 116 psi, and monitored
with a pressure gauge.

After first night, pressure dropped to 102 psi.

After second night, pressure dropped to 92 psi.

This leads me to believe that there's a leak, however, there are no
signs of humidity whatsoever.

Is it possible for a line that shows no humidity (i.e. a line that
presumably has no leaks) to keep loosing pressure?

Is there a logical explanation for this?

Thanks in advance.



Remove NOPSAM to email me. Please let
me know if you have posted also.

The normal way to pressure test heat systems and water pipes is to use air
pressure. It's easier to re-solder if you have a leak.

"mm" wrote in message
...
On Fri, 20 Jan 2006 09:22:53 -0500, Phil Munro
wrote:

116 psi!!! Where did you get WATER at that presure? I always thought
leaks were tested with air presure. Water is not compresible, and
changes in temperature will change the presure, I think. --Phil

Again, no experience, and I thought I would learn about this here.
Some people here seem to have written as if using water is the normal
procedure, but others hint that it's not, or say to use air.

I offer this for the OP's consideration.
Water is only compressible to a slight degree, and the major thing
they could be compressing is the slight amount of air that may be left
in the pipes when they are is filled with water. Because that volume
is small, tThat means that it would only take the loss of a little bit
of air or a little bit of water (giving more room for the air), to
multiply the available space significantly and make the pressure drop
significantly.

Also, the air can get absorbed intio the water. This happens much
faster at high pressures, and iiuc when the air is absorbed in the
water, it takes up no space (amazingly) and thus the pressure would
drop.

Look at the water prssure arrangements in 6-story buildings. (In nyc.
There may be a different height where this applies in other places.)
I think the same thing applies with houses that have wells and
compression tanks.

Four or 5 stories and less, city water pressure is enough, Seven or 9
stories or more, they put a water tank on the roof.

At 6 stories they pump the water into a tank that is about 1/3 air
after the air in the tank is compressed, and they use the air pressure
to pump the water to the sixth floor (and the other floors, but for
the sixth it's essential) After a while the air in the compression
tank has been absorbed into the water, the pressure drops, and a
separate air pump has to be used to add more air. Here the water is
being replaced with new water every time someone uses any water,
unlike the OP's sealed pipe, but there is still absorption to the
extent the original water will take it.

renux wrote:

We're testing a new copper line for leaks.

The line was purged of air, filled with water at 116 psi, and monitored
with a pressure gauge.

After first night, pressure dropped to 102 psi.

After second night, pressure dropped to 92 psi.

This leads me to believe that there's a leak, however, there are no
signs of humidity whatsoever.

Is it possible for a line that shows no humidity (i.e. a line that
presumably has no leaks) to keep loosing pressure?

Is there a logical explanation for this?

Thanks in advance.



Remove NOPSAM to email me. Please let
me know if you have posted also.