Hot pan test - How many bubbles is ok?

Collecting, filtering and dewatering of WVO SVO vegetable oil. For Biodiesel producers too.

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Hot pan test - How many bubbles is ok?

Postby tubular031 » Mon May 11, 2009 3:09 pm

My last 2 batches of oil have been a pain. I heat the oil to 150 and settle for 24 hours. Then I drian off about 2 to 3 gal and do a HPT. If I see bubbles, I drain another 2 to 3 gal and test again. these last 2 batches have has a few small bubbles with NO crackles.

The last bacth I pumped into a storage barrel to deal with later. This batch is in the water heater still. I drained 5 gal from the 35 that it started and I still saw some small bubbles. I heated it back up to 150 again last night and will test again when I get home.

But how many bubbles is too many? I have read where people say any bubbles is too many and I have also read people say that a few small bubbles is ok as long as there is no crackel and the VO is clear.
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Postby John Galt » Mon May 11, 2009 7:06 pm

But how many bubbles is too many?
ANY bubbles is a sign of water in the fuel. How much water do you consider acceptable, how much is your IP worth, how much will it cost to rebuild or replace when it fails due to water damage? Modern computer controlled fuel systems with rotary IPs are very sensitive to any water in the fuel. Older inline IPs typically used in mechanically controlled fuel systems are much more tolerant of moisture in the fuel.
Some people believe that some amount of rodent feces in their food is acceptable, others don't. Everyone has to find their own level of acceptable contamination. There are no absolute Yes or No answers.
more info here:
http://www.burnveg.com/forum/viewtopic.php?t=72
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Re: Hot pan test - How many bubbles is ok?

Postby SunWizard » Mon May 11, 2009 10:31 pm

tubular031 wrote:But how many bubbles is too many?

Any is too many since its easy to dewater so there are no bubbles. A crackle is hugely too much water for any IP.
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Postby David » Tue May 12, 2009 1:17 am

I'm not surprised you are getting bubbles.
While I see lots of people say that the heat and settle gets rid of all the water, I can't see how it is possible myself with dissolved water. I tend to think this works mainly because people either don't test but assume or their standards to pass the test are a little more relaxed than mine.
Free water, no question I can see that working but to get the oil perfectly dry, I have my reservations.

Even if it does get the oil 100% dry ( for our purposes) I hardly see it as being particularly efficient.
Reading about the huge amount of energy many people pump into their oil to heat it to dry or settle it also re-assures me I'm ion the right track with my evaporation method that uses 300W for 90 min, or less than 1Kw/hr of electricity.
The Bubble method also seems to work and is energy minimal although it can take some considerable time on oil.

I always get my oil dry enough to pass a stinking hot pan test with a complete absence of bubbles. Some people who have seen my set up and watched me pull a drum of oil from a pile at their choosing and test it with not a single bubble, seem to be amazed but I do it every time with a minimum of effort.

If the heat and settle isn't getting you to where you want to be, check out some different approaches. You can't expect to get different results from doing the same thing so maybe another method will work better for you.
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Postby tubular031 » Tue May 12, 2009 7:57 am

John Galt wrote:
But how many bubbles is too many?
Some people believe that some amount of rodent feces in their food is acceptable, others don't. Everyone has to find their own level of acceptable contamination. There are no absolute Yes or No answers.
more info here:
http://www.burnveg.com/forum/viewtopic.php?t=72


That is a very interesting way to put it. I dont like the idea of rat turds but then again if its causing me no harm, I dont really care. Its like eatting a hot dog, do you stop to think what is really in there?

I think I am going to try an upflow system like you use john. I should have all the parts sitting around to take a whack at it. I just dont like the slow introduction of oil. I get all my oil from 55 gal drums that I supply restruants. If I got my oil in the jugs slowly pouring the oil in would make more sense. maybe I need to pump the oil from the barrel to a jug and pour. Gotta think about this a little more.


David wrote:I'm not surprised you are getting bubbles.
While I see lots of people say that the heat and settle gets rid of all the water, I can't see how it is possible myself with dissolved water. I tend to think this works mainly because people either don't test but assume or their standards to pass the test are a little more relaxed than mine.
Free water, no question I can see that working but to get the oil perfectly dry, I have my reservations.

Even if it does get the oil 100% dry ( for our purposes) I hardly see it as being particularly efficient.
Reading about the huge amount of energy many people pump into their oil to heat it to dry or settle it also re-assures me I'm ion the right track with my evaporation method that uses 300W for 90 min, or less than 1Kw/hr of electricity.
The Bubble method also seems to work and is energy minimal although it can take some considerable time on oil.

I always get my oil dry enough to pass a stinking hot pan test with a complete absence of bubbles. Some people who have seen my set up and watched me pull a drum of oil from a pile at their choosing and test it with not a single bubble, seem to be amazed but I do it every time with a minimum of effort.

If the heat and settle isn't getting you to where you want to be, check out some different approaches. You can't expect to get different results from doing the same thing so maybe another method will work better for you.


I am starting to agree with you. Heating and settling is not seeming to cut it for me. I read all over about the frybird still and the success many have with it, but I am having a hard time getting to zero bubbles. Guess they are just passing less then perfect oil.

I really want a gravity fed centrafuge, and I was almost ready for one till the start of this year and work started cutting our pay.... stupid economy :(

Do you have a link or something to your setup? I am interested. I am using 1100 watts for about 2.5 hours to heat my oil up to 150. I am not to worried about the 50 cents it costs in power to heat the oil, I am more interested in a better dewater design
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http://www.burnveg.com/forum/viewtopic.php?t=623
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Postby John Galt » Tue May 12, 2009 12:49 pm

That is a very interesting way to put it. I dont like the idea of rat turds but then again if its causing me no harm, I dont really care. Its like eatting a hot dog, do you stop to think what is really in there?
I have... that's one of the many reasons I don't eat hot dogs or 'processed' meat.

I think I am going to try an upflow system like you use john. I should have all the parts sitting around to take a whack at it. I just dont like the slow introduction of oil. I get all my oil from 55 gal drums that I supply restruants. If I got my oil in the jugs slowly pouring the oil in would make more sense. maybe I need to pump the oil from the barrel to a jug and pour. Gotta think about this a little more.
How about pumping from the top of the barrel into the upper reservoir of the upflow, then letting it slowly flow through the upflow cell?
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Postby WD8CDH » Tue May 12, 2009 3:51 pm

David wrote:I'm not surprised you are getting bubbles.
While I see lots of people say that the heat and settle gets rid of all the water, I can't see how it is possible myself with dissolved water. I tend to think this works mainly because people either don't test but assume or their standards to pass the test are a little more relaxed than mine.
Free water, no question I can see that working but to get the oil perfectly dry, I have my reservations.

Even if it does get the oil 100% dry ( for our purposes) I hardly see it as being particularly efficient.
Reading about the huge amount of energy many people pump into their oil to heat it to dry or settle it also re-assures me I'm ion the right track with my evaporation method that uses 300W for 90 min, or less than 1Kw/hr of electricity.
The Bubble method also seems to work and is energy minimal although it can take some considerable time on oil.

I always get my oil dry enough to pass a stinking hot pan test with a complete absence of bubbles. Some people who have seen my set up and watched me pull a drum of oil from a pile at their choosing and test it with not a single bubble, seem to be amazed but I do it every time with a minimum of effort.

<snip>


Heat and settle won't won't remove dissolved water but neither will evaporation. Heated evaporation will actually increase dissolved water because oil will hold more dissolved water at higher temperatures and turn some suspended water into dissolved water. The hot pan test doesn't show dissolved water very well, only suspended or free water. (Hot pan test often shows a false negative for dissolved water)

When oil with dissolved water is cooled, over time, that dissolved water becomes suspended water and can harm your engine.

Since heat and settle is at lower temperatures than evaporative methods, as long as convection currents are minimized, settling will result in truly dryer oil than evaporative drying.

I use a controlled heated upflow settling method that due to good insulation uses less than 60 watts that even with high fat/hydrogenated oil gives me far below 250ppm total water (free, suspended and dissolved) as verified by Karl Fischer method.
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Postby kirkharrod » Wed May 13, 2009 12:23 pm

I heat to 120* and settle in an insulation wrapped 5 gallon steel barrel first,

and THEN put it through an unheated upflow barrel,

then through an inline water heater element heater

then through a 10 micron spin on filter

then through a 5 micron spin on filter

and into the collection barrel.

I get ZERO bubbles with this method!
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