Sciencemadness Discussion Board

Diaphragm pump + aspirator no B.P. change?

Opylation - 3-6-2020 at 12:09

Hello everyone,

I have a serious issue that has been bugging me for a few days. So I have had this diaphragm pump that I’ve been using for about a month or so in series with an aspirator to provide vacuum. Now, it is the exact same pump nurdrage has on his video about the same device. Just for sake of disclosure I’ll list the specifics labeled on the front of it.

Title: micro diaphragm pump
Voltage: DC12V
Power(Max): 60W
Pressure(Max): 0.8Mpa
Flow(Max): 5L/min

The device came with the power supply wires cut and soldered so I went ahead and bought a 12V 5A power supply and a female power cable to match the male plug on the power supply. Soldered everything up and sealed each solder joint with heat shrinking electrical tubing and have the whole pump hung up the side of a tote with magnets.

So I’ve been using this thing to pull a vacuum on my 250ml fritted disk Büchner funnel and it usually takes 15-30 seconds to run through a filled funnel. Now the other night I tried to distill a high boiling viscous liquid under my aspiration vacuum and noticed that the B.P. was about the same as what it would be at atmospheric pressure. I couldn’t be 100% accurate because my thermometer only marks to 200C but leaves space for about another 100C and it was around what it should of been at atm. Anyways, this befuddled me. I finished the run anyways, losses a decent amount to high temp polymerization, it was a disappointment.

Well, cut to today and I decided to run some water through my setup to calculate my systems pressure using the B.P. of water. I set everything up and lo and behold B.P. is 100C. I’m watching the aspirator, which I have hanging below the water line and I’m not seeing any air bubbles being pushed out the exit. When the system is benign depressurized I can see the water steam leaving the aspirator is turbulent with many many bubbles. But once under vacuum, the exit stream is flowing but void of air.

Now, to make sure everything was alright I decided to thread each joint in the aspirator with ptfe tape to make sure there was no leakage. I also removed the back flow stopper leading to the distillation system in case for some reason there was blockage. I noticed that the port on the aspirator that leads to the distillation setup, that takeoff adapter was super glued, including the o-ring to the aspirator. I had to break that glue when I took it apart to remove the back flow stopper. But I have made sure to leave a healthy amount of ptfe tape to make sure once again there is no leakage.

Lastly, my distillation system is connect via ground glass joints. Joint size is 24/40 everywhere. I secure the joints seal with 2 rings of ptfe tape. One at the bottom, once around, and one at the top, once around. I also make sure to give each joint a good twist to make sure it’s nice and snug. Also, when I shut off the pump, water creeps up the tube connecting my aspirator to my distillation setup decently quick like it’s flowing from high pressure to low pressure. All in all, everything is looking like it’s functioning properly, but boiling points do not lie. I am absolutely lost as to why I’m not seeing even a single degree off of the regular boiling points of different liquids.

If anybody could help that would be amazing. I am at a loss as to why it seems to be producing pressure but not enough to affect B.P.

[Edited on 3-6-2020 by Opylation]

Ubya - 3-6-2020 at 12:25

well, it is strange, you said that you could not see any bubbles in the aspirator outlet, so it reached its maximum vacuum, but the boiling point doesn't change.
the boiling point is pretty sensitive to ambient pressure, if you don't see even a 1 degree difference is odd.

Opylation - 3-6-2020 at 12:27

I’m running the system without vacuum right now and the thermometer is running at 105C so it is a little bit over submerged. With that said, I guess I was getting ~5C off of B.P. This is disappointing though as nurdrage was able to boil water at ambient temperature using ice cold water through his pump/aspirator

Ubya - 3-6-2020 at 12:29

Quote: Originally posted by Opylation  
I’m running the system without vacuum right now and the thermometer is running at 105C so it is a little bit over submerged. With that said, I guess I was getting ~5C off of B.P. This is disappointing though as nurdrage was able to boil water at ambient temperature using ice cold water through his pump/aspirator


i have the same pump, and i could get water to boil at 70°C, it's not a great pump, maybe nurdrage got a good one and us got a cheaper and crappier version with the same look, or our diaphragm pumps lie about their specs

Opylation - 3-6-2020 at 12:35

Apparently. I guess it’s only pulling ~100mmHg under ambient pressure which is, as I said disappointing. I might throw in for a 3 gpm pump. We’ll see. Especially if I’m not even seeing a dent on the b.p. of those high boiling liquids. I was hoping there was some sort of troubleshooting I could do before having to dish out for a new pump. I just don’t know enough about these things to know if there even is anything wrong with it

[Edited on 3-6-2020 by Opylation]

Ubya - 3-6-2020 at 12:49

can you post a picture of the setup? maybe we can figure something out

Opylation - 3-6-2020 at 13:25

Yeah sure thing. The water is emptied hour of the aspirator system right now because it’s not in use. Just boiling some water to get a new supply of distilled water but here are some pics of how it would look set up.

EB2BF22E-060C-4951-90B1-D45C61353B61.jpeg - 81kB B043197C-00FB-4127-85E8-4A8EEF3355DF.jpeg - 84kB 293F73E5-A576-4CC0-8110-7BBA80719189.jpeg - 70kB 05E5A5CB-B70B-46CE-A6B3-04AAF9696980.jpeg - 87kB

Uhh... not sure why the pictures are sideways. I hope it’s alright


Also, I went overkill with the ptfe tape to make sure it wasn’t a leakage issue

[Edited on 3-6-2020 by Opylation]

Ubya - 3-6-2020 at 13:43

mh you should connect a piece of tubing (20-30cm) to the outlet of the aspirator, and then put the end on the tubing a few cm underwater, it should improve the system a bit

this is my setup
WhatsApp Image 2018-03-11 at 17.41.49.jpeg - 174kB

[Edited on 3-6-2020 by Ubya]

Opylation - 3-6-2020 at 14:06

Normally the output is submerged below the water line so I can keep track of when the system has pulled its max vacuum. I did have a foot and a half long rubber tube on the exit but I didn’t see a difference in the performance so I just removed it

beerwiz - 3-6-2020 at 14:07

The water in the tank needs to be cold. The problem with setups like yours is that the water heats up and the vacuum gets very weak. I've had all kinds of rotary vanes, pump setups like yours, etc. I've spent thousands on pumps over the years. Now I just use an aspirator connected to the faucet, it's perfect for vacuum distillations, and the cold water from the faucet runs at a constant temperature. Another benefit is that it's quiet and any fumes get washed down the drain and you have no oil mist to deal with.

Ubya - 3-6-2020 at 14:22

Quote: Originally posted by beerwiz  
The water in the tank needs to be cold. The problem with setups like yours is that the water heats up and the vacuum gets very weak. I've had all kinds of rotary vanes, pump setups like yours, etc. I've spent thousands on pumps over the years. Now I just use an aspirator connected to the faucet, it's perfect for vacuum distillations, and the cold water from the faucet runs at a constant temperature. Another benefit is that it's quiet and any fumes get washed down the drain and you have no oil mist to deal with.


ehhh if water was infinite and free (and i had a faucet near my hood).
even if it isn't for the money, a distillation of a few hours wastes a lot of water

Opylation - 3-6-2020 at 14:28

The thing is I had ice in my vacuum water reservoir and it still wasn’t showing me any change on b.p. (This was when I was trying to vacuum distill that high boiling liquid the other day) my thermometer was hitting around 250C, +-10C, right where it’s B.P. was. Even without cold water I feel like I should at least get 30-40C off b.p., right?

Ubya - 3-6-2020 at 15:37

as a qulitative test, run the pump and put your thumb on the vacuum hose, feel the vacuum. now try with another piece of tubing, stick on end on your mouth and start sucking while you have your thumb on the other end. with your mouth you can create more or less half a bar of negative pressure, if your pump pulls less, you got an idea of your vacuum.
(if you can get a cheap vacuum meter is bettery, they are a few bucks on ebay)

Opylation - 3-6-2020 at 21:37

So I tried that. I put the suction end on the top of my tongue... barely pulled anything. I felt it start pulling more and more vacuum for 10-15 seconds then, nothing, just stayed there. Honestly, wasn’t barely anything... I wonder if my pump is broken. Or, I watched a video where some vacuum pumps have an auto feature for when they’re installed in RV’s and shit and when they meet a certain amount of resistance they turn off or turn the flow rate down. Maybe that’s the case. I wonder if I can calibrate it

Opylation - 3-6-2020 at 22:16

Now that I’m looking closer at my pump I think the whole thing is a fraudulent one. On the front facing display with all the info diaphragm is spelled wrong...

image.jpg - 2.3MB

monolithic - 4-6-2020 at 13:54

Trying orienting your aspirator so it is ejecting water straight down.

Opylation - 4-6-2020 at 14:56

I’m thinking about maybe trying to get a different motor for it. Cause the pump works, it’s just only pull a very weak vacuum. The motor inside it was a ghs-775ph-4458xx I can’t remember exactly but if I get a motor with more torque it should be able to pull more of a vacuum

Opylation - 4-6-2020 at 19:48

Could it be my aspirator? Because now that I think about it I see people connect aspirators to faucets that couldn’t have a greater flow rate than the pump I have. When i first got my aspirator, I noticed the o-ring was super glued on the vacuum take-off port and I broke the seal when unscrewing the port. I got more super glue a little bit ago and re-glued it to make sure the seal was fine. When I took the thing apart to re-glue it I noticed my jet nozzle was skewed, about a single radius Of the jet nozzle distance off of the exit port. Another way to say it is looking down the jet nozzle leading to the exit nozzle only half of the jet hole lined up with the exit hole. Does this reduce the vacuum generated?

[Edited on 5-6-2020 by Opylation]

Sulaiman - 4-6-2020 at 20:04

Try connecting your aspirator to a faucet and see if it works as expected.
If yes then the pump is inadequate,
if not then the aspirator is faulty.

Opylation - 4-6-2020 at 22:53

Are diaphragm pumps supposed to be loud? It’s been running at 65-70dB since I got it. I was looking at other pumps online that look the exact same and they’re rated as quiet

Sulaiman - 5-6-2020 at 06:58

Did you make the sound level measurement at 1m from the pump ?

None of my pumps are 'quiet' (I have many types)

Have you tried the aspirator on a faucet yet ?
with and without a pipe/tube on the outlet.

Ubya - 5-6-2020 at 07:54

Quote: Originally posted by Opylation  
Are diaphragm pumps supposed to be loud? It’s been running at 65-70dB since I got it. I was looking at other pumps online that look the exact same and they’re rated as quiet


no they are not quite, mine is pretty loud, and the vibrations get even amplified by my hood. i plan on mounting the whole pump/water tank on vibration absorbing material and soft things so to muffle the sound a bit

Opylation - 5-6-2020 at 13:41

Okay, I was just curious if my pump came damaged or something. Well, I did a test and if the flow is blocked the pump is able to build up decent pressure. Enough pressure to break my ptfe seal to my aspirator so I’m gonna look for an adapter to connect the 18mm threading to the 3/8” compression fitting on my aspirator. I’m not familiar at all with piping so it’s gonna be a struggle. Also, I wonder if a pressure regulator would work. Something that prevents flow until a certain pressure is met. That way the pump can build up a working pressure and then send that pressurized flow through the aspirator. I’m missing something though. The aspirator and the pump both look like they are working but I am just not getting any vacuum. 100mmHg below atm at the most which is not gonna work for vacuum distillations. I don’t know if I need greater psi in my aspirator input or greater flow overall. Also my pump has duel fitting for the hookups. 18mm thread and 10mm push connect which I’ve been using. I’m not sure if using the smaller hookup is restricting the flow of the pump and I should just use the threaded connection. So many ifs. I think I’m gonna start with the 18mm to 3/8” compression fem to fem adapter and see what happens. If the vacuum still is sufficient I’ll probably have to get a higher psi pumps. I’ve been looking at a 60W 130psi pump that would work with the power supply I’ve already bought. I have a spare 5.5mm by 2.1mm cable for the power supply

Ubya - 5-6-2020 at 14:34

Quote: Originally posted by Opylation  
Okay, I was just curious if my pump came damaged or something. Well, I did a test and if the flow is blocked the pump is able to build up decent pressure. Enough pressure to break my ptfe seal to my aspirator so I’m gonna look for an adapter to connect the 18mm threading to the 3/8” compression fitting on my aspirator. I’m not familiar at all with piping so it’s gonna be a struggle. Also, I wonder if a pressure regulator would work. Something that prevents flow until a certain pressure is met. That way the pump can build up a working pressure and then send that pressurized flow through the aspirator. I’m missing something though. The aspirator and the pump both look like they are working but I am just not getting any vacuum. 100mmHg below atm at the most which is not gonna work for vacuum distillations. I don’t know if I need greater psi in my aspirator input or greater flow overall. Also my pump has duel fitting for the hookups. 18mm thread and 10mm push connect which I’ve been using. I’m not sure if using the smaller hookup is restricting the flow of the pump and I should just use the threaded connection. So many ifs. I think I’m gonna start with the 18mm to 3/8” compression fem to fem adapter and see what happens. If the vacuum still is sufficient I’ll probably have to get a higher psi pumps. I’ve been looking at a 60W 130psi pump that would work with the power supply I’ve already bought. I have a spare 5.5mm by 2.1mm cable for the power supply

the less restrictions you can get, the better the system, as you can see the aspirator needs quite a lot of water flow to function properly

Opylation - 5-6-2020 at 21:10

I finally splurged for a better pump. 130 psi 70w very similar design. So either things will look up or I will be a fool out more money. The thing is the aspirator is literally the exact same one as nurdrages so I’m inclined to say it’s the pump. The issue is the pump needs to “charge up” the water pressure But I’m not sure what to do about that. When I place my finger over the exit, I’m able to stop the flow for 5-10 second before the pressure builds up enough to force its way through. If my new pump plays the same song and dance I’m gonna have to McGyver something. Maybe a ball valve on the exit flow of the aspirator and wait until the pressure builds to open it.

Also, this time it’s being shipped from America so I feel more confident

[Edited on 6-6-2020 by Opylation]

Sulaiman - 5-6-2020 at 21:22

As your power supply is 12V 5A (60W) it may not work with a 70W pump.

Opylation - 6-6-2020 at 05:08

My first pump was $10 from China so I think they gave me a fake pump or switched the tags. The word diaphragm is spelled wrong on the front. This time I got a good ol’ American brand shipped from America so hopefully all is well on this one. I hate to be a broken record but I can’t get over the amazing results nurdrage got with the exact same style pump and identical aspirator. We shall see

Opylation - 15-6-2020 at 14:02

Alright, I got my new pump in the mail and I soldered things up and put it together. One thing I noticed is the pump is quite a bit quieter than my last one. It is still noisey but it isn’t really loud. Like the difference between something hitting a materials resonance frequency and making the whole material vibrate. I would say this new pump is at least 1/4 - 1/2 as noisey. I haven’t put it through a distillation run but I did a quick suction test against my finger and it feels like it pulls more of a vacuum, but it only feels like it pulls maybe a little more than twice the vacuum of the previous pump. I guess we will see what happens when I hook it up to my glassware. The pump is advertised as being compatible with a high pressure switch but I didn’t notice anything different between the wires of the old pump and the new pump. I have a 6a 12v power supply powering the pump since it’s rated at 70W however I noticed in the front the voltage says 12 (9-14.4)V and 6A so I don’t know if I’m losing some power by keeping the voltage at 12 instead of maxing out the voltage. Idk, I guess we’ll see

[Edited on 15-6-2020 by Opylation]