Download
Harmless
Posts: 22
Registered: 29-1-2018
Member Is Offline
Mood: No Mood
|
|
Cheap chinese diaphragm pumps?
Looking on Aliexpress there seems to be two types that are commonly sold.
A smaller and cheaper one and a slightly more advanced looking one.
Has anyone given these a shot? I was hoping to know how good a vacuum they can get. Some of the listings give a value for "suction" in metres but it's
a bit inconsistent. Some say they'll do 0.8MPa (~80m head), will work with gasses and they're self priming, so I'd think they should be able to do an
okay vacuum. Might need to grease the valves though.
I'm mostly looking for something that will do 1-10kPa absolute. So not groundbreaking stuff, just something for distillations.
|
|
|
B(a)P
International Hazard
Posts: 1139
Registered: 29-9-2019
Member Is Offline
Mood: Festive
|
|
I have recently installed something similar to the 'slightly more advanced' looking one in a camper trailer to feed the tap over the kitchen sink. The
outlet of the tap is approximately 200 mm above the top of the supply tank. When the tank is full the pump will only just self prime. When the tank is
half empty (~400 mm of head) the pump will not self prime.
There is no way my pump would pull or push 80 m of head.
The pump is also quite loud.
|
|
|
unionised
International Hazard
Posts: 5128
Registered: 1-11-2003
Location: UK
Member Is Offline
Mood: No Mood
|
|
No pump could draw a head of 80 feet (or draw a vacuum of minus seven bar absolute- which is essentially the real problem)
If a pump is quoting that figure then it's either wrong (deliberately or accidentally) or it's a pressure, not a vacuum.
On the other hand I used to use a diaphragm pump for vacuum filtration in the lab and it was quite capable of boiling acetonitrile or methanol. A good
one is certainly capable of drawing a vacuum much better than 400 mm H2O.
Essentially, B(a)P has been sold a lemon.
|
|
|
Mush
National Hazard
Posts: 633
Registered: 27-12-2008
Member Is Offline
Mood: No Mood
|
|
Quote: Originally posted by Download  | Looking on Aliexpress there seems to be two types that are commonly sold.
A smaller and cheaper one and a slightly more advanced looking one.
Has anyone given these a shot? I was hoping to know how good a vacuum they can get. Some of the listings give a value for "suction" in metres but it's
a bit inconsistent. Some say they'll do 0.8MPa (~80m head), will work with gasses and they're self priming, so I'd think they should be able to do an
okay vacuum. Might need to grease the valves though.
I'm mostly looking for something that will do 1-10kPa absolute. So not groundbreaking stuff, just something for distillations. |
https://www.youtube.com/watch?v=tYLlkTDstmo
|
|
|
Dr.Bob
International Hazard
Posts: 2750
Registered: 26-1-2011
Location: USA - NC
Member Is Offline
Mood: No Mood
|
|
Those pumps are designed for water pumping, so they typically will not pull much of a vacuum. Ones designed for vacuum will do much better at
pulling a vacuum than those designed for water. And trhose are small pumps, the 12V one by definition will be weak, as the amperage needed for even
a small vacuum pump won;t work well at 12V.
I would look for a used vacuum pump on Ebay; laboport, KNF, Welch, and VWR all make diaphram pumps for rotovaps, they are on Ebay often, som e for
reasonable prices.
|
|
|
monolithic
Hazard to Others
Posts: 436
Registered: 5-3-2018
Member Is Offline
Mood: No Mood
|
|
To add to what Dr. Bob said, I bought a used KNF pump identical to this for $175 shipped a few years ago. https://www.ebay.com/itm/KNF-Neuberger-UN726-3-FTP-Diaphragm...
As long as the diaphragms aren't torn, they're pretty much bulletproof with PTFE/FFKM pumping parts. Highly recommend this model if you want to invest
money in a good pump as it's rated at 10 torr when configured in serial pumping mode (I've measured 12-15 torr.)
|
|
|
Mateo_swe
National Hazard
Posts: 548
Registered: 24-8-2019
Location: Within EU
Member Is Offline
|
|
If you want a cheap setup for vacuum then get a water pump, the ones looking like your "slightly more advanced" pump and use it to pump water from an
ice bucket into a aspirator so the water circulates from and into the bucket with ice water.
That will give a decent vacuum from the aspirator side port that can be used for distillations.
And the aspirator isnt sensitive for corrosive chemicals and gases but remember they will end up in the circulating water.
Good diaphragm pumps are somewhat expensive and the cheap small ones as the one in your first example can only be used for filtrations.
I have not tried use the small ones for any distillations but i think they are way to weak.
|
|
|
RustyShackleford
Hazard to Others
Posts: 200
Registered: 10-12-2020
Location: Northern Europe
Member Is Offline
|
|
Aspirator builds are hit or miss. The one i built (according to nurdrages video) can barely pull to 0.8atm, absolute shit.i even got the same chinese
"brand" and specced pump. pump cost like 25 bucks and the aspirator like 10, at that point its better to just throw in an extra 20 and get a cheapo
mechanical one.
I know of 2 other people who had the same experience building their own aspirator setup.
[Edited on 17-12-2020 by RustyShackleford]
|
|
|
monolithic
Hazard to Others
Posts: 436
Registered: 5-3-2018
Member Is Offline
Mood: No Mood
|
|
| Quote: Originally posted by RustyShackleford | Aspirator builds are hit or miss. The one i built (according to nurdrages video) can barely pull to 0.8atm, absolute shit.i even got the same chinese
"brand" and specced pump. pump cost like 25 bucks and the aspirator like 10, at that point its better to just throw in an extra 20 and get a cheapo
mechanical one.
I know of 2 other people who had the same experience building their own aspirator setup.
[Edited on 17-12-2020 by RustyShackleford] |
I wonder why people have varied success with those types of builds. I briefly owned a lab grade recirculating aspirator pump (Buchi B169) and it
pulled very good vacuum, definitely close to its 20 mbar spec. They're built in a similar fashion to the DIY types -- maybe the type of pump has
something to do with it? I think the Buchi had a centrifugal pump feeding the venturi aspirator.
|
|
|
RustyShackleford
Hazard to Others
Posts: 200
Registered: 10-12-2020
Location: Northern Europe
Member Is Offline
|
|
| Quote: Originally posted by monolithic | | maybe the type of pump has something to do with it? I think the Buchi had a centrifugal pump feeding the venturi aspirator. |
Could be. most homebrew setups including mine use membrane pumps.
|
|
|
SoundClown
Harmless
Posts: 17
Registered: 17-12-2018
Location: Narnia, USA
Member Is Offline
Mood: Hungry Like the Wolf
|
|
https://www.ebay.com/itm/Black-12V-DC-Brushless-Small-Water-...
From the US, uses a common power supply and relatively easy to work with for distillation and reflux
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
