Sciencemadness Discussion Board

Vacuum filtration & possibly distillation without mechanical pump!

RogueRose - 18-1-2016 at 19:15

I've been trying to figure out a way to pull a vacuum on a low budget or with things on hand (or easily available). I came up with the idea of using an old propane tank (empty) with a modified valve (replaced or modified to accept 2 way flow with a valve that can close).

A hose is needed to connect the filtrate receiver to the propane tank.

Open the valve on the tank (must allow free flowing gas in and out of valve) and place on fire - a propane turkey fryer would probably be a good source. Heat for a few minutes until the tank is throuroughly heated. This will cause most of the air to expand as it is heated. The valve can be closed at this point to retain the partial vacuum or it can be attached to the hose and vacuum will be pulled as the tank cools.

I think it would be beneficial to perform the filtration immediately to take advantage of the slow pressure build up (slow vacuum draw) instead of taking the chance of the tank collapsing under too much vacuum.

Now there are risks with this. Fortunately I don't think an imploding/collapsing tank is nearly as dangerous as an exploding one -PLEASE inform me/us if there are unstated dangers.

A few things to note - the larger the tank, the more vacuum that can be pulled and a more even vacuum will be drawn over the period of filtration. The higher the tank is heated the more the air expands, pulling more vacuum.

Do NOT rush the cooling by trying to cool the tank with cold water as it can degrade the temper of the metal or even cause implosion. if a speeded vacuum is required, use a fan blowing onto the tank if this is a must.

I would venture a guess that if the tank passes the pressure tests for a refill it should be capable of holding the vacuum.

The following is the percent of increase in volume of air from an ambient temp of 72F. I know humidity comes into facotr here but I don't have that figured in yet.

It looks like to pull 1/2 bar the air needs to be heated to 600F which is an increase of 100% - or doubled in size. When cooled, that means there is 1/2 the air in the tank as what should be there at ambient temp. At 1150F it heats to 200% so you can pull 2/3 bar.

Ambient Temp 72
Deg F
120 9.03%
212 26.35%
300 42.91%
400 61.72%
500 80.54%
600 99.36%
700 118.18%
800 137.00%
900 155.81%
1150 202.93%
1200 212.27%
1350 240.50%
1500 268.72%
1650 296.95%
1800 325.18%
2000 362.82%

[Edited on 19-1-2016 by RogueRose]

j_sum1 - 18-1-2016 at 19:27

The problem I see is inability to control how much vacuum is being pulled.
I think you would do better to fit a venturi device to a water tap. Check out Doug's Lab youtube channel to see how this looks.

Detonationology - 18-1-2016 at 19:30

Sounds like a cool idea... but also sounds like a bomb...

BromicAcid - 18-1-2016 at 19:31

Another issue is that the seals in the valves for those sort of propane cylinders were designed to be used at standard temperatures. At elevated temperatures, even if the valve is not heated directly, your seals/gaskets may fail and in the case of trying to maintain the vacuum this could cause your plan to fall apart quickly. Also I do not think that your container will be able to contain enough 'vacuum' for anything other than a filtration or so, and if you are not there to immediately stop it once your filtration starts to pull air you will quickly run through your hard work.

Oscilllator - 18-1-2016 at 19:41

Another way you could do this is to add a bit of water to the tank, so the tank ends up full of steam instead of hot air. Not only will this contract more as the steam turns to liquid water, but the temperature should be at a maximum of 100 degrees.

XeonTheMGPony - 18-1-2016 at 22:56

A 20 pound tank will take out a small house This is a simple steam explosion if the valve where ever to fuse.

Way way too much risk and good way to kill onse self for a craptastical amount of vacuum volume.

better off using your vacuum cleaner then this!

XeonTheMGPony - 19-1-2016 at 07:42

Now after a good nights sleep head is a bit more clearer.

If all you need is a vacuum for filtering. A vacuum cleaner with a suction bleeder to allow motor cooling. Or you can fabricate a simple venturie by using a T fiting and and a copper stub tube with a 45 degree cut end inside the T to about mide diameter, this will notproduce a monster vacuum but should be enough for most needs.

Dr.Bob - 19-1-2016 at 08:37

If vacuum did not leak, a "stored" vacuum might work, but few systems don;t leak vacuum at a huge rate, filtrations being among the worst. So if you don't have a consistent way to keep generating a vacuum, a filtration will stop within seconds. Just use a water aspirator or even a small wet dry vacuum or other trivial vacuum source, but the heated propane tank is a bad idea for many reasons.

Bert - 19-1-2016 at 08:56

Cheap centrifugal sump pump from harbor freight. Water aspirator type vacuum pump. Garden hose. Garbage can or large Tupperware bin filled with ice and water. Electrical outlet.

Hardly ever blows up the house, doesn't run up your parents water bill, or annoy them when the water pressure is always low in the shower.

If you simply MUST use an heat powered system with no electrics, learn about the history of such things- start here:

Steam punk vacuum system...

RogueRose - 20-1-2016 at 05:44

I'm really confused how so many people think that a smallish tank under vacuum will take out a house, let alone a room. First, the tank has to be ABLE to fail under the vacuum created, which as I have shown, isn't going to pull 1 bar no matter how hot you heat it. I know an empty propane tank doesn't implode at 150ft of water which is about 5 ATM or 75 PSI of outer pressure (assuming a 1 ATM inner pressure that is a 60 PSI difference).

If the tank were heated to 1200F you would have a maximum of 10PSI of vacuum pressure. I think the tank will hold. Even if it were to implode at this pressure, very little damage would occur other than possibly falling over and rolling a bit.

I really like the idea of using a little water in the bottom to create steam, which will later condense. I have not looked into the numbers with this so I can not comment on the numbers and saftey of this procedure.

I know there are other ways of generating vacuum but I thought the point of this forum was to explore various possibilities and support them with relevant information, logical assesments and point out actual possible downsides - not to immediately give other alternatives (basically thread hijacking) which have been covered ad-naseum, explain possibilities of the opposite of what is trying to be achieved (making the tank a bomb - which EXPLODES not implodes - with exception of certain nuclear devices which use that as a trigger, not as end goal...).

The point is that this could have been a good thread, with the intelligent people who participate in this forum I am amazed that none of you know this will work or have used it - or maybe you have and then that leads to an entirely different thread.

As for storing "vacuum" I didn't mean to keep it for weeks or months, simple minutes while doing a setup of filtration or whatever.

If any of you can prove this is a totally bad idea, I'll send you a gift card for $50 to your store of choice.

[Edited on 20-1-2016 by RogueRose]

j_sum1 - 20-1-2016 at 05:54

I think you misunderstood something.
Oscilllator suggested putting a bit of water in the tank before you heat it up. Then it is not filled with air but steam. When it cools it condenses which results in a far larger volume change than cooling air and so is able to pull vacuum for longer.

Nice idea. But Xeon exposed a flaw in it. It is possible to cause the bottle to explode while heating the steam inside it. I think you could take steps to avoid it (ie, open the valve properly). But enough accidents have happened with repurposed gas bottles to ask questions and give everything good consideration.

Bromic Acid also raised a very good point -- the design of the seals. They may not take heat cycles so well and even if they do, they are designed for a positive pressure difference and not a negative one.

Myself, I think the idea fails on functionality. You are going to have quite a strong vacuum initially which will reduce over time. And all you have to control it is an unregulated valve. The system will have a lot of inertia and will not be easy to operate. It's a novel idea, but I think there are more practical ones.

Dr.Bob - 20-1-2016 at 06:12

The idea fails on not working. You can store compressed air practically, because a tank can hold many atmospheres of pressure, thus storing 10 or 100 atm of pressure, which is a useful amount. But a vacuum tank can only store 1 atm of vacuum, no matter how good a pump you use, so you cannot store vacuum practically, as the container needed would be too large. A 5 gal tank cannot hold more than 5 gal of vacuum, which will drop quickly, after 2.5 gal are gone, the vacuum will be only 1/2 an atm, which is useless. It is well established that storing vacuum is not practical for most purposes. Just find a simple pump or aspirator, they work well, and are used by most scientists to generate a vacuum.

XeonTheMGPony - 20-1-2016 at 07:06

I do mechanical refrigeration, and I have re-used propane tanks in both Vacuum and pressure they work well.

MOP = 300psi, Vacuum as deep as you can pull.
MWP=280 psi

The Valves do have an integral pressure relief on newer ones.

When you heat steel you alter its mechanical properties called annealing

So weakened steel, fire/heat, potential fused valve in closed position can equal boom.

Water aspirated vacuum system driven by pump is best option.

MOP = Max operating pressure
MWP = Max Working Pressure

[Edited on 20-1-2016 by XeonTheMGPony]

wg48 - 20-1-2016 at 07:16

I think the bottle is unlikely to fail under vacuum and if it did fail its unlikely to cause serous damage. However just like a large CRT tube failing, occasionally a pieces of glass are expelled from the implosion that can cause serous injury.

I expect that gas bottles are manufactured from steel with some ductility so if they tend to rupture instead of fragmenting. Also many have burst discs or over pressure relief valves.

Of cause thinking the bottle will not fail and cause serious damage is not the same as knowing it will not. If I needed too I would try it myself but I do not recommend anyone else trying it.

The condensed steam idea will be effective in say pulling a litre of fluid through a filter if the bottle has a few or more litres capacity.

As others have said a venture type pump will do the job and even a crude one can pull up a meter of water and don't forget a fridge compressor can be used to create a vacuum. There a long thread on that presumably explaining the limitations and problems.

Even aquarium pump that can be modified to suck and can dramaticly increase the speed of a filtration.

But note that when all the liquid has been sucked through the filter and air is pulled through it leaves the solids relatively dry compared to gravity filtering but to do that you need a higher vacuum with a higher flow rate.

Praxichys - 20-1-2016 at 07:46

I don't think anyone mentioned a hand vacuum pump yet. It's a pain in the hand but it gets the job done.

immunetoN-rays - 27-4-2016 at 20:29

When I was quite young and had no vacuum aspirator (didn't know what one was), I used 2 filter flasks. I put a little water in one and boiled it until it was pretty much full of steam. The top was open . Then I took it off the heat and put a cork in the top, and as the water condensed it sucked air through the sidearm which was connected by a tube to the other flask's sidearm. vacuum filtration! To work well, you need a LARGE filter flask for the heated one. You're really a lot better off with an aspirator.
If you have a car I suppose you could use manifold vacuum, but then you'd need to leave your car idling as you filtered. If you try to use this for a vacuum distillation, be sure you have plenty of gas!
For completely non-mechanical vacuum distillation there's the Charles technique: Mix zinc and acid and catch the gas in a balloon. Then use the balloon to elevate your distillation setup to an altitude where the pressure is lower. For high vacuum work wear a pressure suit.

NedsHead - 27-4-2016 at 22:36

Quote: Originally posted by immunetoN-rays  
If you have a car I suppose you could use manifold vacuum, but then you'd need to leave your car idling as you filtered.

The MAP sensor will detect a fault and either shut the vehicle down completely (if you're lucky) or put the engine through hell trying to compensate for the fault. it could end up costing you a lot of money replacing an engine or paying an auto electrician to restore a fault code with the computer. I wouldn’t risk it

immunetoN-rays - 28-4-2016 at 19:14

Not that it was a serious suggestion, But I meant a REAL car. Not one of these new-fangled flibbertigibbets with their MAP sensors, and brake boosters, and starters that active themselves when you turn the key.
I drive a pickup so old it's got 5 pedals on the floor and a manual choke to boot. I've had mechanics insist it was broken because they couldn't figure out how to make it go.

j_sum1 - 28-4-2016 at 19:30

five pedals???

NedsHead - 29-4-2016 at 02:23

I've driven tractors with 3 pedals + accelerator, but 5 pedals? it must be a nightmare to drive in city conditions.

[Edited on 29-4-2016 by NedsHead]

Cheap vacuum pump

tshirtdr1 - 29-4-2016 at 03:46

Harbor freight has cheap vacuum pumps. They even have a $20 one, but I cannot attest to its effectiveness. They have some for $99 and $159 if you can swing that.

arkoma - 29-4-2016 at 07:16

Quote: Originally posted by XeonTheMGPony  

better off using your vacuum cleaner then this!

Been there, done that!

XeonTheMGPony - 29-4-2016 at 08:28

Quote: Originally posted by arkoma  
Quote: Originally posted by XeonTheMGPony  

better off using your vacuum cleaner then this!

Been there, done that!

I know it really sucks eh ;)

Another option is a gravity vacuum pump.

Fill a very large bottle full of water, put lid on, drive the suction tube through the lid till it hits the bottom, place the drain tube in just through the lid. Hang the bottle upside down high as you can, to start the vacuum simply open the drain valve!

Larger the bottle the longer the vacuum runs for, higher it is deeper the vacuum to a point.

zenos2 - 29-4-2016 at 17:33

Agree with Dr. Bob and others.. for filtration's and such, this would die quickly. Pick up a cheap nalgene or such aspirator for ~$12+ on Amazon or Ebay. I recently upgraded to a SS model for about $17 and have had no issues with it.

I built an adapter that connects to a water hose outlet for about $5 from hardware store parts, and even have my vac line running about 30' through a hard plastic (HDPE?) 1/4" water supply line that holds up to anything I've inadvertently put through it, including HNO and NOx fumes, and doesn't collapse.