Deairing water 1

[gbowen]

In geotechnical testing labs it is common for water used ing testing to be deaired. For example, triaxial testing and permeability testing. There are many deairing units available for sale but have relatively small capacities. I am considering building one for our new lab and am interested in any ideas or experiences people have with deairing tanks.

 

[Focht3]

What size do you need?



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See faq158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"

 

[gbowen]

I would like to be able to deair at least 5 gallons at a time and as much as 30 gallons a day. We have approximately 20 triaxial/permeability chambers.

 

[Focht3]

That's a lot of water to de-air. I'd think that some large Schedule 40 PVC (say, 12 to 24 inch) pipe would work well. It should be good for more than 100 psi, so 15 psi of vacuum wouldn't be a problem. It's pretty cheap, readily available, easily machined/cut/glued. And you can get the capacity you want by adjusting the size and length.

The only drawback? You can't visually inspect it for algae, etc.

Plexiglas will also work, but will cost a great deal more. I'd avoid a metal container.

A cheap, temporary de-airing tank? Try a 5 gallon drinking water bottle, rubber stopper, tubing and vacuum grease -



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See faq158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"

 

[plp]

I just got done building a deairing tank for use in the field. It's made of clear 8"PVC from

http://www.Harvel.com.

I spray the water into the vacuum tight cylinder from the top and have level switches and a pump on the bottom to drain out the deaired water. I can do about 2-3 gpm. The whole system cost around $800. It is now obsolete as we just purchased a membrane contactor from

http://www.liquicel.com

that reduces our parts and gets air constituents down to ppb levels at 5-10 gpm. I can get you more details on either system if interested.

 

[gbowen]

Any details would be great. I am going to be building my system before the end of the year and am looking for any tips I can get.

 

[plp]

I'm new to this forum so I'm not sure if there is a limit on how much to post, which will correlate on how much detail to post. Anyway, we are using the Liquicel membrane now, because you have water flowing in one end, water flowing out the other, and a separate line for the vacuum. As the water goes through the cylinder, almost all the air gets sucked out through a hydrophobic material. A contactor for your application would probably cost about $3000-$4000. Nice for us in the field because less parts to break down. The cheaper (monetarily) route took about 2 months to design and build. It holds a vacuum of 30in Hg for days. You could process your water sample fairly quickly and recirculate the water to make sure all the air is removed. It is actually available now as I think we well abandon it if this contactor is all it claims to be. You would pressurize your sample through the nozzle, then suck the air out with a vacuum compressor. You'll know how much air was removed with a pressure gauge on the compressor side, plus you'll stop seeing bubbles produced in the water reservoir. I can forward pics/plans etc.

 

[gbowen]

plp

This is very useful information. I would like to see the pics/plans you have and am going to consider the Liquicel membrane as well. It sounds like it might be within our budget. I am going to be gathering information for the next month or so and start building or purchasing a device by the end of the year.

Is there a URL you can post where I can view the pictures?

 

[harney]

The University of Washington geotechnical labs have been employing a "cyclical" deairing system for more than a decade now. The units were constructed in-house, designed primarily by graduate students, and basically consist of 2 deairing tanks that work cyclically--while one unit is being drained, the other is filling/deairing. The units were built primarily to run very long-term permeability and/or geotextile filter compatibility tests. Using a series of solenoids and float valves allows the control of water inflow and outflow, as well as the application of vacuum. The tanks themselves, as Focht3 suggested above, are made of Schedule 40 PVC and are each ~36 inches tall--no durability issues in 10+ yrs. Small clear acrylic standpipes were mounted on the side of each tank to check levels. Water is sprayed in (after being filtered) under vacuum to achieve efficient deairing. Never had any problems (in 10+ yrs) with biological or algae buildup. The system performed so well that other research groups became interested, and a second-generation system was built in 2000 that incorporates most of the same features of the first, but includes an outflow pump and some minor design upgrades (there were some nice "lessons learned" from the first tanks). I don't believe the system was ever specifically detailed in any technical articles or papers--maybe it should be. The only reference that contains significant information I know of is Greg Fischer's (one of the original designers) PhD Dissertation "THe Influence of Fabric Pore Structure on the Behavior of Geotextile Filters," University of Washington, 1994, 498pp. Available on-loan from your local academic institution or by UMI. If you're using *a lot* of deaired water, this is a nice option--basically an "unlimited supply." The tanks do take about 35 minutes to fill under vacuum, so draining one faster than that causes problems by throwing the solenoid sequencing off, etc etc (but rarely have we ever drained so much deaired water so fast under test conditions). I'd be pleased to provide some additional information on the system at request.

 

[plp]

I got the liquicel membrane contactor today and it seems to be built very well. I'll be setting up a test for this week. I think I'll flow water through the liquicel first and deair it. The output of the liquicel will pressurize through the previously built degas chamber. Any air that makes it into the degas chamber slipped though the liquicel. Our degas chamber sounds similar to harney's above and was based on an article titled "Measurement of krypton 85 in the ocean" by Smethie and Mathieu. Published in Marine Chemistry, 18 (1986) 17-33. Currently I don't have a site to post pics but could email some files.

 

[gbowen]

I would like you to email the files but the forum will not allow posting of email addresses. I tried last time but it was deleted. I appreciate your help and would like to hear how the liquicel performs.

 

[Ron]

gbowen... I'm fairly sure there is no prohibition of posting email addresses for contact as long as it is not for solicitation or other commercial purposes. Just for communication is OK, keeping in mind that there are many who will then have access to your email. There is also a means of private contact through commenting on the thread to the author.

We used to use a large water bottle as Focht3 pointed out. It worked fine.