Sciencemadness Discussion Board

KNF UN726.3 FTP vacuum pump for sale!

monolithic - 22-12-2018 at 11:02

I'm selling my KNF UN726.3 FTP vacuum pump. The manual and specifications can be found here: https://www.knfusa.com/?type=5600&file=2237

It "should" be able to pull a 10 torr vacuum but a quick test with water and a nomograph indicates ~80 torr maximum maximum. I'm not sure why. I disassembled the pump and the diaphragms, valves, etc. are all in good working order, and I wrapped the threaded connections in a fresh layer of Teflon plumbers tape. At any rate, it works just fine while drawing an 80 torr vacuum and the chemical resistance of the PTFE heads/diaphragms and FFPM valves make it great for dealing with nasty solvents.

I'm asking $175 plus shipping. The box will be 14.5"x13"x10" and weigh ~15 pounds so shipping may be expensive, depending on where you live.

Pictures are available here: https://imgur.com/a/Ab9vdxl

Sulaiman - 23-12-2018 at 04:37

80 Torr is a respectable vacuum for a water aspirator, (water b.p. = c34 oC)
10 Torr would need super-cooled water as 0oC = c15 mm Hg
Probably a lower vapour pressure liquid/mixture would be required.

stoichiometric_steve - 29-12-2018 at 10:21

Quote: Originally posted by monolithic  
~80 torr maximum maximum. I'm not sure why


That sounds like the heads are out of sync or one of them isn't working anymore.

Good luck finding replacements, because KNF stopped making those parts more than a decade ago. It's quite impossible to buy them nowadays.

Quote: Originally posted by Sulaiman  
80 Torr is a respectable vacuum for a water aspirator


Except this is a diaphragm pump. You probably misread and posted something entirely irrelevant.



[Edited on 29-12-2018 by stoichiometric_steve]

morganbw - 29-12-2018 at 10:35

Quote: Originally posted by stoichiometric_steve  
Quote: Originally posted by monolithic  
~80 torr maximum maximum. I'm not sure why


That sounds like the heads are out of sync or one of them isn't working anymore.

Good luck finding replacements, because KNF stopped making those parts more than a decade ago. It's quite impossible to buy them nowadays.

Quote: Originally posted by Sulaiman  
80 Torr is a respectable vacuum for a water aspirator


Except this is a diaphragm pump. You probably misread and posted something entirely irrelevant.



[Edited on 29-12-2018 by stoichiometric_steve]


It is pretty easy to become confused, recent thread by the same author " Buchi B-169 vacuum recirculating aspirator for sale!"
Just saying:)

monolithic - 30-12-2018 at 05:25

Quote: Originally posted by stoichiometric_steve  

That sounds like the heads are out of sync or one of them isn't working anymore.

Good luck finding replacements, because KNF stopped making those parts more than a decade ago. It's quite impossible to buy them nowadays.


It might be as simple as it needing more shims. Each diaphragm is shimmed at the connecting rod and PTFE piston interface. I'm not sure how or why they determine the necessary spacing, but it's very important because the manual notes that the shims must not be mixed up or discarded during disassembly or reassembly. As I said, the pistons and valves look to be in very good condition, and the cylinder heads show no signs of corrosion.

I believe they still make parts. When I bought it, the cooling fan on the motor was shattered. One of the repair technicians I contacted had no problem finding a brand new fan. Also, consider that Chemglass still sells the CG-4812-30 vacuum pump, which is a rebranded UN726.3 FTP.

Update: I disassembled everything and checked it over one more time. Reassembled and I managed to distill some glycerin at about 155C. I'm at nearly at sea level, so the nomograph indicates ~13 torr of vacuum. Looks like it does work at its rated vacuum. :)

[Edited on 30-12-2018 by monolithic]