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Today's water puzzle.
2

Today's water puzzle.

Today's water puzzle.

(OP)



I've got a puzzle.
Here's a water-hammer buffer/accumulator.

The pressure is just about exactly 100psi. Note the purple tag down near the bottom? That's where the water reached initially. Over a period of 6 months the water has crept to where you see it now. This has been repeated three times. Eventually it will lock-up, completely filled.

Could the air be dissolving into the water column and leaving or does it have to be leaking out of the top extremely tight plug?

Keith Cress
kcress - http://www.flaminsystems.com

RE: Today's water puzzle.

Inital air pressure at purple tag?

Anyway, tape a balloon on top, covering the cap and sealing to the pipe. Seal it up good (ring of double stick tape on pipe, put balloon on, tape balloon tightly against double stick tape, then tape it some more) and see if the balloon expands at all.

RE: Today's water puzzle.

Dissolving - google "air chambers" to see plenty of discussions. Hammer arresters with bladders are available to eliminate this problem.

RE: Today's water puzzle.

There may be a infinitesimal amount of air that migrates through the plastic, but the bulk of the air is absorbed into the water rendering the air chamber device to be ineffective.

Some plumbing codes still require these air chambers for controlling water hammer. However, both Ballanco and Steele have reported that after conducting laboratory testing, the air chambers are ineffective in controlling water hammer. Myth busted.

Julius Ballanco, P.E., “Water Hammer Control in Small Systems,” Technical Proceedings of the ASPE 1994 Convention, American Society of Plumbing Engineers, Copyright 1995.

Alfred Steele, P.E., Engineered Plumbing Design, Miramar Publishing Company, Copyright 1977.

http://www.siouxchief.com/Resource_/ProductMedia/1...

"A capped stand pipe or air chamber is not an effective solution to controlling water hammer. Since nothing separates the air from the water within an air chamber, it only takes a few short weeks before the air is absorbed into the water, leaving the air chamber waterlogged and completely ineffective. Laboratory tests confirm that the air is depleted by simple air permeation and by interaction between static pressure and flow pressure."

http://www.siouxchief.com/Resource_/ProductMedia/1...

http://www.pdhengineer.com/courses/bd/M-4002.pdf

RE: Today's water puzzle.

Also, that's why boilers need upstream deareators on the BFW to control corrosion. Oxygen dissolves in water. Nitrogen does too.

Good luck,
Latexman

RE: Today's water puzzle.

Have you by any chance soaped the riser and fittings like one does a tire looking for air leaks (other than that, gases can indeed absorb and be scavenged into water flow or turbulence, and in addition can actually permeate at variable rates through various plastics)?

RE: Today's water puzzle.

I agree with most of the above, but the idea of double taping a balloon on a 100 psig system sounds a bit risky.

A better way to do this is with a commercial pulsation damper. In these units, the water is within a bladder inside a pressure containing vessel. You pump up the vessel (around the bladder) with a stem valve like on a tire. There is generally a pressure gauge on the air side to tell you when to top it off.

And yes, you will eventually get permeation of air through plastic, but it is slower than the Henry's Law constant at 100 psig. The air is dissolving into the water and it is probably happening fairly quickly (weeks, not months).

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

RE: Today's water puzzle.

Agreed, air is being absorbed. A common problem with a number of domestic booster pumps found mainly thru out Asia which have an air pocket over the water supply, the air is quickly absorbed and the pumps hunt on and off - the better and naturally more expensive units have a diaphragm at the the air / water interface.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

RE: Today's water puzzle.

(OP)
Great! Learned a lot here. I was just throwing out "absorption" as a wild guess. I'd re-sealed the cap several times, each more aggressive than the previous. I never saw a change in the rate of disappearance.

I think the "disappearance" is way to slow to fill balloons which leak thru diffusion prodigiously, I know because I ran a Dart Throw game :) . Same with the bubble treatment. We're talking maybe 70in3STP 'leaking' out over 1/2 a year. That volume leak might be detectable with a refrigerant tracer but then a refrigerant might attack the PVC or leave right thru it confusing the issue.

The bladder makes total sense. Luckily this particular install only requires loosening a hose to drain the entire tower and restart the 6 month timer.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Today's water puzzle.

Before bladder type pressure tanks became predominant for use in water service from wells, the tanks were bladderless. They were all equipped with diaphragm valve devices that injected a small amount of air into the tank every time the pump started.

http://inspectapedia.com/water/AirVolumeControls.h...

RE: Today's water puzzle.

I agree with previous replies as to where the air went.

I would like to strongly caution you on using PVC for compressed gas service. Even though this is a water line, until ALL the air is dissolved, you have a potential pneumatic bomb.

donf

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