[labnetwork] Recirculating DI water spray guns?

[Kuhn, Jeffrey G]

Mary,

Our circulating DI water guns return the water back to the storage tank via the return loop piping. Since the water is returned to the tank, it is not actually consumed. This configuration uses no more DI water than if our piping were to dead-end at the guns. The only time water is actually consumed is when the guns are in operation.

The issues I see with using a circulating configuration are primarily cost driven. The UPW distribution pump needs to be sized large enough to accommodate the additional flow requirement. The distribution loop equipment (resin & membrane systems, UV, etc.) also need to be sized such that it can handle the additional flow. These things are usually initial design considerations that an existing facility should already be beyond. Other cost factors are that the circulating guns themselves are more costly, and there is additional PVDF piping required to construct the loops.

Personally, I would never use a non-circulating DI water gun unless I was certain that bacteria would not be an issue. You will almost certainly develop bacterial growth in any stagnant DI water piping and hardware. I can personally attest to the ability of bacteria to grow amazingly well in low nutrient environments. Continuous flow is one method of combating bacterial growth in UPW systems; the flow helps prevent them from gaining a "foothold" on the pipe walls. 

I am a bit surprised to hear folks are using non-circulating DI water spray guns. I'd be interested in hearing the logic behind why that is being considered, especially since it doesn't really save any water. However, as I mentioned before if bacteria is not an issue then non-circulating guns may be fine.

I hope this helps somewhat.

Regards,

Jeff Kuhn
Facility Engineer
Birck Nanotechnology Center
Purdue University
1205 W. State St.
West Lafayette, IN 47907
Ph:  (765) 496-8329
Fax: (765) 496-2018



-----Original Message-----
From: labnetwork-bounces at mtl.mit.edu [mailto:labnetwork-bounces at mtl.mit.edu] On Behalf Of Mary Tang
Sent: Thursday, January 17, 2013 2:10 PM
To: labnetwork at mtl.mit.edu
Subject: [labnetwork] Recirculating DI water spray guns?

Dear labnetwork members --

Our wet benches have "recirculating" DI guns to avoid stagnant water lines.  WIth 10 wet benches, this adds up to 50K gallons of DI water each year.  We are in the process of replacing our wet benches.  All of the wet bench providers we've spoken with have said that most of their customers are choosing to use non-recirculating DI spray guns to save 
water.   But I wonder if this may be feasible in certain lab 
environments.  Does anyone have advice and insight to offer?

Mary

--
Mary X. Tang, Ph.D.
Stanford Nanofabrication Facility
Paul G. Allen Room 136, Mail Code 4070
Stanford, CA  94305
(650)723-9980
mtang at stanford.edu
http://snf.stanford.edu



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