Sciencemadness Discussion Board

Water pumps for Distilation

Arcus - 12-5-2021 at 11:07

My water pump broke due to some fault, and I need to buy a new one. Do you know what sort of speed is best for general distillations? eBay sellers have many options: Everything from 180/h to 17000L/h. I thought if it was on the high side it could cause enough pressure to break the glass, but not enough and it wouldn't cool it enough.
Any help is appreciated, as I have not been able to find any useful answers.

[Edited on 12-5-2021 by Arcus]

Oxy - 12-5-2021 at 11:31

You want a pump which will pump the water to the condenser? I am using the cheapest one from hardware store which can pump few l/min.
You don't need enormous speed and pressure for coolant circulation.

Fyndium - 12-5-2021 at 12:18

I suggest using an industrial pressure washer for condenser.

No, really, even the cheapest aquarium or aquaponic pump is more than sufficient for any tabletop distillations. The head might be 30-50cm so the pump circuit must be primed by either lowering the condenser or raising the reservoir, but after that it keeps the water running.

For ejector aspirator pump, things are a bit different. You want at least 5bar pressure with at least 10L/min rated capacity. The ejector will throttle the flow to it's capacity.

B(a)P - 12-5-2021 at 13:36

I run a cheap pond pump. Don't worry too much about flow rate, just make sure the pump can achieve the head you need. Then to deal with the flow rate you can have a recirculation loop before your condenser with a valve on the line going to the condenser and one on the recirculation loop. You can then adjust your flow rate as needed.

RustyShackleford - 12-5-2021 at 15:11

I have been using these small 5 dollar 12VDC cube pumps for years. so far ive only replaced it once, but in retrospect it probably just had some gunk cought in the shaft.
The pump has good water pressure, its able to pump water from the floor to like 2m up without problems in performance. The flowrate is enough that ive never had issues, even with distillations so fast the stream was continuous.

s-l500.jpg - 16kB

Sulaiman - 12-5-2021 at 20:42

At home in UK I use small 5v or 12v d.c. water pumps,
here I'm using a 20W 220Vac submersible pump.

Flow rate is not a problem, very little flow is required.
(you can calculate the temperature rise of the water based on cooling power required (watts), flow rate and specific heat capacity of water)

Head (m or ft.) IS important;
When I use a small reservoir of water (with or without ice) on the bench there is no problem
but when I need to pump from low down (e.g. a bucket on the floor, or a swimming pool)
the available pressure is often not enough,
so, as mentioned above, I can prime the system and then it will keep working as the downwards flow 'sucks up' the upwards flow
- IF there are no air leaks.

The problem is that if for some reason the water circulation fails,
it is difficult to re-prime the system quickly enough to prevent gas/vapour escaping uncondensed.
Depending on what I'm distilling this could be just a nuisance,
or it could allow volatile/combustible/explosive or noxious gasses to escape in bulk.

I feel safer using 5v or 12v dc pumps,
but I do sometimes put my hands in the reservoir with a running 220Vac pump,
they don't kill fish so I expect I'll be ok.

P.S. foam/expanded polystyrene food boxes make excellent ice-water reservoirs

Oxy - 12-5-2021 at 23:41

Yes, when the pump is not so strong it may require to have the reservoir at the condenser's level. I keep the bucket with water next to my distillation setup.
The pump is running on 230V and on the beginning when I started using it I was very cautious when doing any manipulations while it was submerged. It serves me well however, no complains.

Fyndium - 13-5-2021 at 11:59

Very few people seem to understand the concept of "head". Sulaiman got it right on point.

I have survived with low head pumps, but the air bubbles are PITA. Air is dissolved in cold water, but as it heats, the air forms bubbles, which will eventually cause issues with circulation if the pump is not strong enough. The difference seldom has to be 100% of your true head, but something about 20-30% at max will be great, once you prime it. Using decent tubing and never letting reservoir drain completely will ease things.

I use reservoir that has a tap. I can easily drain off warm water and add more cold water without disturbing the circulation.

pneumatician - 22-8-2021 at 17:39

I need a of 750-800 l/h, those of less flow rate is not enough strong to get out in a condenser of 60cm... but every setup is ≠

Sulaiman - 23-8-2021 at 01:46

Just thought I'd mention a few things ;
1) for small centrifugal type water pumps,
the rated pressure is for zero flow rate,
the rated flow rate is with no back pressure,
with intermediate pressures and flowrates almost forming a straight line on a graph.
eg for a pump rated at 240 lph (litres per hour) 300cm head,
pumping water to 150cm above the surface level of the reservoir would give 120 lph flowrate
(actually less due to narrow tubing etc.)

2) 120 lph = 33.3 grammes/second,
so if we allow 10oC temperature rise due to the condenser (Tout - Tin)
the cooling power is 33.3 x 4.2 x 10 = 1400W cooling power for the condenser.
allowing a 20C rise in water temperature, 2800W, etc.

So pneumatician must be using a rather large still ;)

3) In practice, with my 5 litre rbf,
using a pump similar to the one in the photo above,
I typically only get about 1oC temperature rise due to the product condenser, in reflux distillation,
about 3 to 5 oC rise if full speed simple distillation.
(with the reservoir just below the condenser, usually I suspend the collection flask in the reservoir)

[Edited on 23-8-2021 by Sulaiman]

Fyndium - 23-8-2021 at 05:25

I usually run my strip distillations at rate that the device can handle, and most of the time this means constant stream of condensate. 10 liters of 10C water will heat to 40C in ethanol distillation pretty quickly, don't remember exact times, but fast enough to make me mad.

But still(pun intended), small pumps work if you are able to fill the circuit with water, so the water has zero pressure difference and will just move through the coolant system.

horuse10 - 23-8-2021 at 05:44

I always have some freezer pack in the lab freezer.

You can put some in the water and put back those you use in the freezer it's a pretty way to not waster water.

For my new lab i will probably put an 1000L cuve full of water just for cooling purpose.

I prefere use osmosis water for condensers since it doesn't leave scale and iron deposits in.

An another problematic is the development of algea and mud in the water, for this i just put some quaternary ammonium sold as desinfectant cleaner, this permit to conserve the water for monthS if not years !

dextro88 - 23-8-2021 at 08:19

Your best bet woud be to invest in water pump with chiller am this way you wont think of the temperature of the water, they are not the cheapest ones, but i have seen models with even vacum pump option, i hope hove many of you like me wish for somethink like that :D

Or of you more hobby chemist and dont want to invest much funds, you can always use cold tap water for your experiments, or the good ol aquarium pump.

Fyndium - 23-8-2021 at 08:45

Coolant units with reefers tend to be on the more expensive side. We're talking about thousands. Cheaper could be to fill a chest freezer with ice, run a metal spiral tube into it and be mostly happy. Or then, just dump ice into reservoir as it goes.

During winter, it is easy to just dump snow and ice into reservoir. :D Very easy to keep condenser water close to 0C. Last time I dug a 50L bin and filled it with enough water to allow for circulation and dumped the rest with ice and snow. Could run it 2 days straight before refill.

macckone - 23-8-2021 at 09:06

I have four different pumps depending on what I am doing. All are garden pumps from amazon.

pneumatician - 23-8-2021 at 17:04

wow, I purchased another, the old are falling like crazy, and I don't want to die for 20€ of shit, and in this new one say: no use in water over 30 ºC!!!

The heat this days here is crazy, 28-40 ºC, and distilling liters and liters of water, the 300L or more cooling water go to 50 or more ºC!!!

yes, if you ask what I do with 50+ liters of distilled water... I drink it almost all :-)

I see a little device for water cooling in labs but the price are very high (1700€??) and with the electricity prices of today...

[Edited on 24-8-2021 by pneumatician]

pneumatician - 25-8-2021 at 08:02

well, the problem here is the length of condenser and the place where is the pump, if over or under the water outlet condenser... inclusive if you put the cooling water over the condenser the pump is only necessary if you want to return the water in the recipient to cold condenser again.

like someone say + or - the best is two 1000 liters stainless steel tanks, when the upper one is almost empty pump all the water up as many times as necessary, but with this you need a good pump, pipes and taps !!!

Put the tank in the most cold place where the sun does not touch and if you live in a warm site weld refrigerants in the tank !!

if you are only distilling 500 ml of wine or something like this, you don't need anything of this, the water flux for cooling is so low that the water that has already passed through the condenser can be collected in the bucket of cleaning the floors

here is my "master class" of obvious things :-)