Hi Skipsta,
With your filtering funnel, do you get much / any water in it when filling from the service stations?
Cheers
Pete
Hi Skipsta,
With your filtering funnel, do you get much / any water in it when filling from the service stations?
Cheers
Pete
Thanks for the photos Skipsta, I've found that I'm constantly on a learning curve whenever I'm working on or driving the boat.
As I stated earlier, my initial problem was a missing rubber 0-ring on my filler cap, fixed but still have some minor water issues that should be addressed via a new CAV filter monitoring the water trap.
Mantaray your the one who has continually said that condensation in fuel tanks is an urban myth, without offering anything to back up the assertion. You have done nothing to refute the evidence Skipsta , myself and others have quoted.Originally Posted by billfisher
Now who is the one making stupid idiotic irrelevant comments?
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now the first thing you need to do is cut the chase with the smart $rse and irrelevant stupid comments, there is absolutely no call for your stinking attitude with regards totally uncalled for remarks so separate your stinking attitude and leave your sh$t at the door.
and for what you have quoted? then where is your evidence. now water condensation is a myth as there is no way large amounts of water as people asert can be due to condensation and what might be better for you to do is show that it can occur, you know prove your point!
water would have a lot more chance in the volumes reputed to come in via other sources
I wish I could find a report I read on condensation a couple of years back... I think it may have been in Trailer Boat Fisherman Magazine.
A regular writer (from Townsville I think) sat a 20 litre portable tank out beside his shed to deliberately see what happened re: condensation.
The tank:
had about 2 litres of fuel in it,
was covered it in black plastic to stop any rain water getting in,
had the filler cap on, but loose.
He reported that in 1 month, it collected 10 litres of water.
I have read the same sort of thing a while back but can't find it again. It was referring to drag cars (not methanol).
I have a spare 20L can, I'm going to do just that and see what happens. I'll report back weekly.
Here are the humidity figures for Ardrossan, see below:
- Darren
so can't see what sort of a comparison that would be? who covers their boat in black plastic and deliberately leaves the fuel cap on but loosethe general idea is to make sure the filler cap is secure and tight? well normal people do. why not simply close the tank filler properly and sit the tank in the sun?
I'm no expert by any stretch Mantaray, but I think the point of having the filler cap on but loose (or alternatively leaving the breather loose) is to match what happens in an inbuilt alloy tank. They are not a closed system, they have an external breather that prevents the tank from buckling/splitting under great pressures.
If you were to keep the portable tank fully sealed, of course no water can get in, but as the air is full of water, especially in QLD, surely it goes some way to explain how water gets into a tank. Air sucked in containing water, water condenses, falls into fuel, dry air flows back out?
I know my system. With all my precautions and contingencies, water is still getting in, albeit in much smaller amounts. Where is it coming from, if not from condensation?
Pete, not as yet, I think dodgy fuel is a bit of a rarity.... But it does happen. I know that I got a very bad does of fuel in my Rodeo's fuel tank (At least 5 litres) which wrecked my fuel pump.
There is a small reservoir of about 50mkl in the bottom which is where the water would collect, I just chuck this bit containing water/fuel whatever. Haven't actually seen any water in it yet though
I am becoming a bit paranoid with my boat. You all probably would too, if it broke down 3 times out of 4 trips
I now have 2 engines, 2 batteries, 2 radios, 2 fuel filters, 2 fire extinguishers. At least I know I can get my arse back home
As Mr Bean's chart shows the highest humidity in Ardrossan is late night and early morning when temp differences are least.
During the day when the temp differences are highest the humidity is at it's lowest, and this is when the air is being sucked into tanks.
If you live in Qld you will realise that our particular brand of humidity can live a life of its own sometimes.
There is still plenty of moisture laden air in Ardrossan in summer however.
I like the expansion chamber idea using a bag around the breather vent that was mentioned earlier. regards
Well, lets get this sorted.
Get the relative humidity
RelHum = relative humidity in %
Get the air temperature
Tcenti = air temp in degrees C
Calculate the saturation vapor pressure Esat
Esat = 6.11 * 10# ^ (7.5 * Tcenti / (237.7 + Tcenti))
Calculate the vapor pressure Evap
Evap = (RelHum * Esat) / 100
Calculate the dewpoint temperature K
Kdpoint = (-430.22 + 237.7 * Log(Evap)) / (-Log(Evap) + 19.08)
Add the sign
If Kdpoint >= 0 Then dpsigns = "+"
Or Else
dpsigns = "-"
Working through the equation, you will see that a typical Brisbane day works out at a dewpoint of around 22 degrees.
So, how do we achieve a dew point of 22 degrees in a fuel tank in the middle of the Australian Summer?
Easy..
The evaporation of fuel.
Now, at standard temperature and pressure (STP), (STP = 1 atmosphere at 25 degrees) unleaded fuel will readily evaporate. (additives are added to increase evaporation point in hotter climates, but this example is designed to be all encompassing)
The evaporation causes cooling (the same as the wet hessian bag over the meat safe when camping)
Now, everyone would have washed their hands in petrol and noticed how cool it feels??
Cooling by Evaporation - the cooling effect is not a constant temperature, but is easily less than 22 degrees, more like 10 - 15 degress (estimate)
So, when the direct sun temperature is approximately 50 degrees, it causes the tank to expand (everyone has seen / heard the mower fuel tin when left in the sun?)
The expansion of the tank draws in humid air through the breather.
The hotter the day, the more expansion, the more evaporation of the fuel, the more rapid the evaporative cooling effect, and due to this evaporative cooling, condensation is forming instantly as this process occurs. The condensing effect is not directly related to the temperature of the day, but the higher the temps and the higher the humidity, the worse the effect. (hence the difference between Qld & SA)
In a sealed tank without a breather, the tank expands but does not keep creating condensation on an ongoing basis, as new moisture is not introduced regularly. (same with motor cars with positively pressurised tanks, portable sealed plastic boat tanks - they can only condensate the immediate moisture in the air space available, which is miniscule)
When the ambient temperature drops, or even fluctuates, the tank breathes air, constantly, just as we do - in / out / in / out. Keeping in mind that the evaporated fuel is constantly condensating any new moisture in this air, it doesnt take long to build up a mass of water.
The higher the fluctuation in the ambient temperature, the more breathing the tank can do - the more condensation collected.
Rapid evaporation can actually freeze water vapour at 14 degrees (ever heard of frozen carbies in older planes / racecars, vehicles operated in the Antarctic?)
Now, add FNQ Cairns's diffusion theory, and the facts stated by Impulse 492f on how much water vapour is held in the atmosphere (Humidity)(assuming calculated at 100%), combined with the unlimited breathing ability of the tank, and the fact that water is condensating instantly due to the evaporative cooling effect, then it is possible to assume that:
An average, half full 200 litre tank could condensate 8 mls of water per full breathing cycle, given that a tank may breathe fully 2 - 3 times a day, given location and changing sun / shade conditions.
This works out at a very real 112ml to 168ml per week... this ties in with most people constantly having "a little bit of water in their fuel"
If the tank is kept full, it reduces the breathing ability of the tank and virtually reduces this equation to nil water.
Skipsta just answered your questions, the portable tank filler was left loose and covered in plastic to simulate the worst available conditions in a breathable or unsealed tank. Nobody leaves their sealed tanks undone when stored - it was done for demonstration purposes.
Any unsealed tank (ie tank with breathing capabilities, boat or otherwise) is succeptible to high levels of condensation.
Water can come from other sources, I agree, but this should answer your questions of how / why / when condensation forms in unsealed tanks.
Any
I hope this gives you enough technical backup to prove why condensation can be a problem with unsealed tanks.
Regards
Pete
Well I have no further comments.
why not put a moisture trap on the breather pipe?
You know, just like a moisture trap on an air compressor.
Then it's virtually a closed system.
ie http://www.mit.edu/people/robot/diesel/index.html
30C/86F 30 grams/cubic meter[quote author=Mantaray link=1139021238/90#97 date=1139644489]now we might have to get a bit techncial here but lets see if some can think through this
how much consdensation can a cubic metre of air hold? anybody
20C/50F 17 grams/cubic meter
10C/13F 9 grams/cubic meter
A cubic meter equals 264 gallons of liquid volume, therefore:
A 200 gallon tank = 0.76 cubic meter.
At 86F, an empty 200 gallon tank could contain 22.8 grams of water vapor, or 0.81 oz.
At 50F, an empty 200 gallon tank could contain 12.92 grams of water vapor, or 0.46 oz.
In order to condense water out of the atmosphere a surface must be much colder than the air.
Any other quizz Mantaray.
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[smiley=oops.gif] my oh my oh my impluse you might not have any further comments but i got one for yousomebody has just pointed out where you got the above from
http://www.yachtsurvey.com/myth_of_c...fuel_tanks.htm
so why didn't you put the infomation forward impluse [smiley=leer.gif] what not the right outcome
What about a flexible breather like a corrugated hose of some kind that you could seal off with a valve but still have enough stretch to take up the increase in volume of a warm tank?????
Hmmmmmm
cheers jon
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