# Shattered filtering flasks!



## autumnwillow (Apr 18, 2018)

So I was filtering a pregnant AR today when the filtering flask imploded, liquid was everywhere. We used a tissue paper to capture all the golden liquid and threw it in a pvc bucket, we then added SMB to this bucket until solution was clear. I'll incinerate tomorrow then melt. 

Out of the 7 filtering flasks that I had, 5 of them imploded, 1 was dropped accidentally and now only one remains. Although these flasks were modified erlenmeyer flasks to have a tubulation. I guess that was the cause, or its age(1 year of use). I always check for cracks.

What are your experiences with filtering flasks?
I'm using a 7cfm vacuum pump, I think the filter paper should have been broken first if the filtering flask that I was using is a good quality, or maybe AR boiling due to low pressure?

I'm also thinking of buying the six pack at this site, http://www.capitolscientific.com/Co...-Wall-Filtering-Flask-with-Sidearm-Tubulation.
It will be also used as a reaction vessel.


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## nickvc (Apr 18, 2018)

My advice is buy only the best ones when using a vacuum pump for the reason you are now cleaning up, cheap ones are a false economy if you are doing regular refining and recovery.


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## g_axelsson (Apr 18, 2018)

I hope no one was hurt in the accident.

Exactly what do you mean with


autumnwillow said:


> Although these flasks were modified erlenmeyer flasks to have a tubulation.


Did you use standard erlenmeyer flasks and not the special buchner flasks? Then it was only an accident waiting to happen. Slightest crack or even just bumping into it while pulling a vacuum might put it over the stress limit.

When you pull a vacuum you can at most pull the atmosphere pressure at about 1 kg per square centimeter. That is 150 kg on a surface as big as your hand. Erlenmeyer flasks are made thin to handle thermal stresses well while buchner flasks are thick walled to withstand the external pressure from the atmosphere.

As you have noticed, when one flask imploded the fragments were enough to crack any flask in the vicinity and the implosions propagate. 

My half liter buchner flask has four to five mm thick walls, I would never use anything as flimsy as a standard erlenmeyer flask with vacuum.

Anyone wanting to see what vacuum can do should watch the episode of mythbusters where they implode a railway tank wagon.

Göran


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## autumnwillow (Apr 18, 2018)

I asked a laboratory glass shop to add a pipe at the side as it originally did not have any.

If I buy those pyrex filtering flasks can it withstand the full vacuum of my current pump? Its a two stage 7 cfm, forgot the micron rating. This will really help me fix my filtering problems. I saw how fast the liquid was passing thru the filter before it imploded.

I knew it was going to break sooner or later so I actually had the filtering flask placed inside a bucket, this contained most of the liquid but still there were a lot of liquid all over the room. Well, next time I'll wrap the filtering flask with plastic wrapper.


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## autumnwillow (Apr 18, 2018)

I just watched the mythbuster video, he said 23" Hg. Pyrex filtering flasks claims it can withstand 30" Hg. Maybe I should buy a vacuum pressure gauge to go with it? And just to be safe I'll try to keep it at 25" Hg.


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## Shark (Apr 18, 2018)

While I am not working on as large scale as most here are I use the nalgene flasks quite often. They are polypropylene and not good for all situations I am sure, but there is no risk of flying glass. Even then I want a couple of good glass flask to go with them. 

https://www.amazon.com/dp/B003OBZ2EQ/ref=twister_B004O6NF76?_encoding=UTF8&psc=1


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## snoman701 (Apr 18, 2018)

autumnwillow said:


> I knew it was going to break sooner or later so I actually had the filtering flask placed inside a bucket, this contained most of the liquid but still there were a lot of liquid all over the room. Well, next time I'll wrap the filtering flask with plastic wrapper.



I'm not the mayor of safety town...in fact, I'm not even allowed in the city limits anymore...but if you were in the USA and someone had been hurt when it broke, you could be found guilty of gross negligence for knowing the risk and proceeding anyway. I post that most for other people than yourself. 

It's however quite rare that I'm using a filtration flask on anything that doesn't equal or exceed the cost of a proper filtration fask. 

You should be fine with a proper filtration flask, but personally I'd want to add a scrubber or two inline before your vacuum pump. I also add a T with a valve and a gauge, so that I can keep actual vacuum below 25, any further and you can pop holes in thin papers.

Glassware used under vacuum should also be inspected for scratches. If it has excessive scratching, you should take it to a glass blower and have them anneal it, or gauge the damage for you.


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## g_axelsson (Apr 18, 2018)

30 inch Hg is the maximum vacuum you can pull and to be fair, water starts to boil until it freezes at that pressure so you will probably never go past 25 while filtering liquids. It is the surrounding atmosphere that pushes inwards and when you remove the gas on the inside you remove the support that pushes back. It is the pressure of the surrounding atmosphere that sets the maximum pressure differential.

To go over 30 inch Hg you have to work in a pressure chamber, so with proper buchner flasks I wouldn't worry about pulling a too high vacuum. A gauge is good to see what vacuum you are pulling and to see if filters are clogged or the vacuum is bad.

Göran


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## anachronism (Apr 20, 2018)

You need to use a vacuum regulator willow. Your vacuum is building too high hence the destruction of the flask.


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## autumnwillow (Apr 20, 2018)

snoman701 said:


> I'm not the mayor of safety town...in fact, I'm not even allowed in the city limits anymore...but if you were in the USA and someone had been hurt when it broke, you could be found guilty of gross negligence for knowing the risk and proceeding anyway. I post that most for other people than yourself.


I agree. I knew it was going to happen sooner or later. It is only now that I'm trying to find solutions for a problem that has been existing for a year now. Definitely my fault for those poor flasks imploding.



g_axelsson said:


> 30 inch Hg is the maximum vacuum you can pull and to be fair, water starts to boil until it freezes at that pressure so you will probably never go past 25 while filtering liquids. It is the surrounding atmosphere that pushes inwards and when you remove the gas on the inside you remove the support that pushes back. It is the pressure of the surrounding atmosphere that sets the maximum pressure differential.
> Göran


Since it was a gold chloride liquid if it was a pyrex filtering flask under good condition, it should have boiled first correct?



anachronism said:


> You need to use a vacuum regulator willow. Your vacuum is building too high hence the destruction of the flask.


Makes a lot of sense, since the worker pouring in the funnel won't have time to view the vacuum gauge and adjust the pressure if it starts to rise, which actually happens really quick.

I actually decided to go for just a 2 pc 2L filtering flask, they are cheaper(need to save so i can buy more gold!), just a little bit more work transferring the liquid to another container when its full. I'll play with these flasks for a while until I get confident enough that no filtering flasks will implode, only then will I buy the 4L flasks or maybe something better than those.


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## anachronism (Apr 20, 2018)

Just buy an inline vacuum regulator and you'll never blow a vessel again. Then you don't need to play with anything and check whether things implode or not. It's a one stop fix. The advice is free, you can choose to take it or not.


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## aga (Apr 20, 2018)

To regulate vacuum i used some watering fittings to 'tee' into the pipe, move the gauge off the pump, and added a tap to one of the 'tees'.

Before starting the vac pump, the tap is open, then it gets closed to a point where the gauge reads what is wanted.


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## g_axelsson (Apr 20, 2018)

autumnwillow said:


> g_axelsson said:
> 
> 
> > 30 inch Hg is the maximum vacuum you can pull and to be fair, water starts to boil until it freezes at that pressure so you will probably never go past 25 while filtering liquids. It is the surrounding atmosphere that pushes inwards and when you remove the gas on the inside you remove the support that pushes back. It is the pressure of the surrounding atmosphere that sets the maximum pressure differential.
> ...


Yes, but since it is boiling from it's internal heat it doesn't boil like when you place it on a hot plate. It would probably boil some of the liquid coming from the filter as that is the hottest liquid and any gas dissolved into the liquid also goes off as gas. This cools the liquid down until it is in equilibrium with the pressure and temperature.

The boiling would be hard to see while filtering any liquids.

Here is a demonstration :
https://www.youtube.com/watch?v=glLPMXq6yc0
And for anyone wanting to see more...
https://www.youtube.com/results?search_query=water+boiling+in+vacuum 

I have done this demonstration several times, it's always fun to see peoples reactions when I freeze water by boiling it.  

Göran


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## autumnwillow (Apr 21, 2018)

Am I the only guy here who shattered about 6 filtering flasks in a year and a half?



anachronism said:


> You need to use a vacuum regulator willow. Your vacuum is building too high hence the destruction of the flask.



At what pressure do you set your vacuum regulator at?


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## cuchugold (Apr 21, 2018)

It has been said before, but here it goes again: Avoid glass whenever possible. Use teflon, plastic, metal lined with glass, with ceramic, with fiberglass, with polyurethane, etc, etc, etc. If you insist on using glass, have it all contained within a large spill vessel, etc, etc, etc.

Amazingly everyone focuses on the right/wrong vacuum pressure...


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## autumnwillow (Apr 21, 2018)

cuchugold said:


> It has been said before, but here it goes again: Avoid glass whenever possible. Use teflon, plastic, metal lined with glass, with ceramic, with fiberglass, with polyurethane, etc, etc, etc. If you insist on using glass, have it all contained within a large spill vessel, etc, etc, etc.
> 
> Amazingly everyone focuses on the right/wrong vacuum pressure...



Out of all those items you listed only ceramic will not adhere nor contaminate the AR solution. I do not think a ceramic filtering flask exists.

All of those materials you listed has a possibility to implode with incorrect vacuum pressure.

I use glass(pyrex) so I can observe the liquid, use heat and work faster by taking advantage of its thermal shock resistance.


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## cuchugold (Apr 21, 2018)

My dear fellow human: Use whatever makes you happy. I was trying to be helpful. Godspeed...


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## anachronism (Apr 21, 2018)

Willow

The pressure varies during the cycle. With a new filter paper I keep the vacuum light till it beds in and gets a layer of deposit on the top which then makes it stronger. Then I decrease the pressure further to achieve the flow rate that I want without endangering the integrity of the filter. I have a range of sizes but the largest is 5 litres capacity with a 30cm paper diameter and when set up properly I can leave it to filter and go do other things quite happily in the knowledge that as deposits build up, the vacuum will not constantly increase. 

Cuchu yes there is a range of differing materials you can use without contaminating the AR. On that point I agree with you completely.


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## anachronism (Apr 21, 2018)

autumnwillow said:


> Am I the only guy here who shattered about 6 filtering flasks in a year and a half?



You're the only one who has admitted it that's for sure. 8) I've broken one in 6 years and that was when I upgraded my pumps and got proper vacuum lines so that I had a completely sealed system .With no pressure regulation the vacuum increases and increases until you get a failure in one of the components.


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## snoman701 (Apr 21, 2018)

autumnwillow said:


> Am I the only guy here who shattered about 6 filtering flasks in a year and a half?
> 
> 
> 
> ...



Well...I broke one earlier in the year, but it was while trying to get the rubber stopper in further than it should have went.

But in your defense, you didn't have filtering flasks....you had Erlenmeyer flasks with a barb fitting added. 


Sent from my iPhone using Tapatalk


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## g_axelsson (Apr 21, 2018)

Get a vacuum regulator but use proper filtering flasks. Even with less vacuum how do you know what the safe limit is on a modified Erlenmeyer flask? With proper equipment you know that it can take a full vacuum and not break and still have a proper safety factor.

A vacuum regulator is good for not breaking the filters but you should not rely on it for personal safety.
If you use it to regulate the vacuum to not break flasks then a stuck contact could blow the flasks.

At least, that's my opinion.

Göran


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## aga (Apr 21, 2018)

Yep. Never heard of anyone having a vacuum pump strong enough, or glassware weak enough to smash the glass that way.



anachronism said:


> ... With a new filter paper I keep the vacuum light till it beds in and gets a layer of deposit on the top which then makes it stronger. Then I decrease the pressure further to achieve the flow rate that I want...


Never heard of that before either, but it's seriously Smart and makes absolute sense

That's a Gem to keep for sure. Thanks.


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## kurtak (Apr 22, 2018)

autumnwillow said:


> Out of the 7 filtering flasks that I had, 5 of them imploded, 1 was dropped accidentally and now only one remains. Although these flasks were modified erlenmeyer flasks to have a tubulation. I guess that was the cause, or its age(1 year of use). I always check for cracks.



5 out of 7 :shock: 



> I asked a laboratory glass shop to add a pipe at the side as it originally did not have any.



Been following this - the discussion about vacuum, pressure, regulators, etc. is certainly all good discussion points - but getting to the point of the original question "why are you having a problem with so many filter flasks implode" ?

vacuum, pressure, regulators, etc. are not so much the problem as is the above quotes - as pointed out by some of the other replies



> (Nick posted) My advice is buy only the best ones when using a vacuum pump





> (Goran posted) Did you use standard erlenmeyer flasks and not the special buchner flasks? Then it was only an accident waiting to happen.





> (& again Goran posted) Get a vacuum regulator but use proper filtering flasks.



I am not sure the pic is actually going to show it all that well - but a real filter flask made with a barb (for hooking up the vacuum) is close to if not twice the thickness of a regular flask 

autumnwillow - when you had the laboratory glass shop modify your erlenmeyer flasks did you tell them you wanted that modification done so you could hook up a vacuum "for filtering" ?

If so - they should have told you that an erlenmeyer flask is NOT made to withstand a vacuum when filtering

It is one thing when to use a vacuum to scrub fumes during a reaction - it is another thing when using a vacuum for filtering

When scrubbing fumes in a reaction vessel - if set up right - there should be a tube in the (top) stopper that allows air in as the vacuum pulls fumes out through the scrubber - thereby preventing building pressure on the vessel during operation --- on the other hand - when filtering - the more the filter plugs - the less you have air flowing in & the less air in flow you have the more the pressure builds to the point of "max" pressure being applied to the vessel when the filter is "plugged" to a point of drip --- drip ----- drip ------- drip --------- drip ---------------- drip

Hence the reason actual "filter" flasks being made of thicker glass

Though I have broke a few (filter) flasks in the 7 - 8 years of doing this (usually because of handling like dropping while washing with slippery soapy hands) I have "never" broke one during vacuum filtering & I have often pulled vacuums for extended periods of time on totally plugged filters (walked away during the filtering & came back who knows how long after the filter became totally plugged)

Kurt


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## autumnwillow (Apr 22, 2018)

It was a thick walled erlenmeyer flask that was modified to have a tubulation. I also had one 2L filtering flask(no modifications) break on vacuum.

But it could also possibly be because I also use them as reaction vessels and some are cooled after boiling to reduce waiting time by putting them inside a bucket filled with water.

Cuchugold, I meant no offense.

I saw how fast the liquid was passing thru the filter paper before it imploded, and with that speed filtering should be done in 2 minutes. Do you guys filter like that? If I could achieve that speed with my next order of filtering flasks it'll be great! Since a lot of my refining bottlenecks is actually in the filtering. I actually bought a 240mm buchner funnel, but I don't think the 4L filtering flask can support it. I used a PVC bucket which deforms when the vacuum reaches certain pressure. I'm still trying to figure out where to put it.


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## autumnwillow (Apr 22, 2018)

g_axelsson said:


> If you use it to regulate the vacuum to not break flasks then a stuck contact could blow the flasks.
> Göran



What is a stuck contact?


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## cuchugold (Apr 22, 2018)

No problem willow. Sorry for encroaching your thread. Peace


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## kurtak (Apr 22, 2018)

autumnwillow said:


> It was a thick walled erlenmeyer flask that was modified to have a tubulation.



That may be true but a thick walled erlenmeyer is still thinner then an actual "filter" flask

In my first pic the erlenmeyer IS a thick walled flask & it is about (plus/minus) half the thickness of the filter flask

In this pic we have the (thickest) filter flask (on the left) - then on the right is the same thick walled erlenmeyer as in the first pic - the erlenmeyer in the center is a thin walled erlenmeyer which is again about (plus/minus) half the thickness of the thick walled erlenmeyer

Again - I am not sure how well the pic is going to show the difference in the glass thickness but the glass of my filter flasks is definitely thicker then the glass of my "thick" walled erlenmeyer flasks

Probably the reason I only have 1 thin walled erlenmeyer left is that any other thin walled erlenmeyers I "may" have had have all long ago broke & I avoid using the remaining one unless I actually need it 

Bottom line - get "actual" filter flasks - they are thicker & will take more vacuum - & it certainly can not hurt to add a regulator that will break the vacuum if you exceed the desired vacuum setting of the regulator 

Kurt


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## g_axelsson (Apr 22, 2018)

autumnwillow said:


> g_axelsson said:
> 
> 
> > If you use it to regulate the vacuum to not break flasks then a stuck contact could blow the flasks.
> ...


Usually a vacuum regulator cuts the power to a pump when a certain vacuum is reached and turns it on again when the vacuum is too bad.
If it breaks down without breaking the power to the pump then it is stuck in the on position.

I guess the proper English word would have been a "stuck vacuum switch"... or am I still using the wrong words?
Sorry if my Swedish heritage shines through... :wink: 

In any way, the failure modes for a vacuum regulator is either on or off, the vacuum increases (can be bad) or the vacuum dies off (only a problem for filtering).
Whenever assessing risks, take into concern the probability that something fails in every way possible and the consequence if it does so. The probability and consequence points out where the risks in an operation lies.

We had to use this method and document it well on my old job whenever we did human biological experiments. Connecting electrodes and electrical equipment to humans can be tricky sometimes.  

Göran


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## g_axelsson (Apr 22, 2018)

Thick walled flasks doesn't like strong heating or cooling, that may shatter a flask too. Glass is such a bad conductor of heat so a thick walled flask would have contraction on the cold side and expansion on the hot side, too much and the stresses will break it.

There is a reason there is so thin glass in coffee pots. Thin glass can also flex easier than thick so the stress never becomes as great as in a thick walled container.

Göran


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## 4metals (Apr 22, 2018)

In all my years doing this I have never seen a vacuum receiver implode, and I've seen a few liters filtered! That includes pulling vacuum into and filtering into 4 liter erlenmeyer filter flasks, 19 liter filtering jugs, 10 liter filtering jugs, and 45 liter filtering jugs. (which aren't practical because you cannot lift them to empty them) 

I have broken a few, but from banging them or dropping when cleaning them but no implosions. I do not think the right flask will ever see enough vacuum to break it so I have to ask one question. You said you had these flasks modified. Did the glassblower anneal the glass? If not, or if not done properly (i.e. too fast), not annealing or faulty annealing after fusing on a vacuum stub will weaken the glass.......substantially.


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## autumnwillow (Apr 23, 2018)

To sum it all up the probable causes should only be improper modification of the flask or deterioration by heat.

I had the bleeder valve on when I was filtering so I don't think it was too much vacuum pressure.

Just for the record, I'll list how my filtering flasks broke:
1) Too much vacuum and heat, worker forgot to use the proper stopper with a hole. It only cracked, it didn't implode.
2) Me - vacuum and heat drying of potassium gold cyanide, cracked only, and slight leak.
3) Me - filtering of spent washing liquid of gold, cracked but only the bottom plate of the filtering flask fell off.
4) Worker filtering spent washing liquid of gold, imploded.
5) Worker and me, filtering AR solution, imploded.

In the previous filtering tasks that we did, it was always the filter paper that broke first. It is only maybe it is stronger now because I actually use three of goldsilverpro's wick trick instead of one, they are stacked together in a triangular form because they keep on shrinking due to heat.

Thank you guys for all the help! Filtering flasks will be arriving tomorrow and we can continue with our refining jobs. I only bought the 2L flask this time, a vacuum gauge and cling wrap! I will test how far these flasks can go in terms of vacuum pressure before I go for the 6 pack 4L flasks. If anyone could suggests a better way to filter as I am willing to spend $1000 on the 6 pack filtering flasks then please let me know. Hopefully no more shattered flasks this time!

Edit to add: We were able to recover 25g of gold out of the AR solution that went everywhere, we used tissue and cloth to capture it. Dumped it all in a bucket with liquid, precipitated with SMB without removing the cloth and tissue, washed, pyrolized then incinerated after that we smelted with soda ash and borax.


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## autumnwillow (Apr 25, 2018)

Filtering Flasks came in today.
Compared with what I had, they are way much thicker than the remaining 4L filtering flasks. 
I guess I was ripped off by the laboratory supply who sold me the brand new pyrex claimed "filtering" flasks.
They probably used an erlenmeyer then modified it with tubulation.
The first four I bought was brand new from them.
Even the previous 2L filtering flasks that I bought from them were thin!


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## 4metals (Apr 25, 2018)

Good you were able to get to the bottom of this issue and realize the real culprit was the glass you had wasn’t what it was claimed to be. 

On the bright side you learned a valuable lesson in cleaning up spills and recovering the values from them. That is a skill that is always hard learned but a good one to have. If anyone who has been refining seriously for some time hasn’t had a spill to clean up they’re likely not telling the truth. Spills happen, things break, and recovering the values from those spills is a valuable skill to have.


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## autumnwillow (May 3, 2018)

We are approximately 25grams short!

Does anyone know how to remove the AR liquid from paint? They are in wood and cement paint.


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