Shattered filtering flasks!

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autumnwillow

Well-known member
Joined
Apr 1, 2010
Messages
447
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.
 
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.
 
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
 
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.
 
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.
 
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
 
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.
 
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
 
You need to use a vacuum regulator willow. Your vacuum is building too high hence the destruction of the flask.
 
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.
 
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.
 
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.

vactap.jpg
 
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.
Göran
Since it was a gold chloride liquid if it was a pyrex filtering flask under good condition, it should have boiled first correct?
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. :D

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

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.


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