Sealing NaOH
Sealing NaOH
(OP)
I am looking to select a pump that will dose 4-6 GPM of 25% NaOH at 110ºF.
The big issue I have seen in the past is mechanical seal selection in any NaOH application due to its crystallization when it contacts atmosphere.
Obviously, a double seal would work if the sealing area is starved of oxygen, but the negatives are utility cost needed for a seal support system.
I am inclined to look at a sealless, mag-drive pump.
Any thoughts, experiences, etc.
The big issue I have seen in the past is mechanical seal selection in any NaOH application due to its crystallization when it contacts atmosphere.
Obviously, a double seal would work if the sealing area is starved of oxygen, but the negatives are utility cost needed for a seal support system.
I am inclined to look at a sealless, mag-drive pump.
Any thoughts, experiences, etc.





RE: Sealing NaOH
thread407-207269: Materials selection for Pump (32% Caustic)
thread407-115830: Pump selection help needed for tank circulation...
Patricia Lougheed
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RE: Sealing NaOH
You may want to consider a peristaltic type...
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RE: Sealing NaOH
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Non-pulsing flow (like with peristaltic pumps) is eliminated, and no danger if hose/tube fails.
You are correct that the air/liquid interface is the biggest seal problem. Note mag-drives don't like running dry, but this one is as forgiving as any I've used.
RE: Sealing NaOH
Yet, my issue now is differential pressure abilities.
I need to provide 200 PSI differential at 6 GPM......the helical gear and peristaltic fall short and the centrifugal would have to have a 10" impeller or up and would be very inefficient at that low of flow/high head.
RE: Sealing NaOH
A multi-stage centrifugal with a double mechanical seal, such as one of side-channel pumps offered by Grundfos, might be something to look at. A thermosiphon-cooled buffer fluid system won't cost you much in utilities.
The other option is a diaphragm PD pump. Seal-less, reliable, but inefficient and produces pulsile flow. At 6 gpm you could buy a triplex unit and get rid of the pulsing. But it'll cost you...6 gpm's a lot of flow for one of these.
RE: Sealing NaOH
RE: Sealing NaOH
Packed gland was mentioned, but the problem with Caustic is the formation of crystal as the liquid comes into contact with atmosphere, seal life is always a factor to consider, mag-drive is an absolute first class choice for such liquid, and have served withour maintenance or service for many years - do watch the temperature of Caustic - if it drops below 20'C then it has a very steep viscous curve - a common cause of those beloved 'pump problems' that people like to shout at manufacturers about !!
Sorry if this is sales man talk here but www.cdrpumps.co.uk have just the animal - usually very quick delivery, and used widely in these applications !!
Ash Fenn
www.cdrpumps.co.uk
RE: Sealing NaOH
RE: Sealing NaOH
Ultimately, I am going with a regenerative turbine pump with a seal quench stariving the sealing area from oxygen. The quench will not require any additional utility costs over and above operating the pump.
The end user went with this option due to the low purchase price of the pump.
RE: Sealing NaOH
RE: Sealing NaOH
As a piping plan 62, it will have continuously quench, not accumulating crystals. Perhaps a rotating bellows seal can help to have a free displacement of the rotating element (bellows) even with a little build up of crystals, in case of a piping plan 62 failure, but bellows seals use to be more expensive than pusher seals tough.
Hope it helps.
Mario Souza
Application & Product Engineering
WMF Solutions Brazil
http://www.wmfsolutions.com
RE: Sealing NaOH
Another option is an unpressurized dual seal with Plan 52. The buffer fluid will help keep oxidation from occuring within the seal.
A third option is something called active lift or upstream pumping. This is another version of an unpressurized seal but utilizes a simplified support system- water supply to a reservoir only. There was a paper on this presented at the 2005 Pump Symposium.
RE: Sealing NaOH
http://www.verderflex.com/PRD_Peristaltic_Pump.php
And as the hose is the only wearing part maintaniance costs are reduced
RE: Sealing NaOH
Investigate the Upstream pumping seal Longeron mentions above. This is effetively a tandem seal with very simple utilities attached, it will solve your crystalization problem and provide a reliable secondary seal.
Good Luck
RE: Sealing NaOH