Chalker
Well-Known Member
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Fuel polishing
- Thread starter drew silverwitch
- Start date
Chalker
Well-Known Member
I bought a replacement Jabsco pump for my HR recently. "Not suitable for continuous use with diesel". WTF!!!!!
PaulRainbow
Well-Known Member
What's the formula for those calculations ?
superheat6k
Well-Known Member
No idea ! However, prior threads on here have thoroughly de-bunked the idea that cold tank condensation has any real contribution to water gathering in diesel fuel tanks.
However if you wish to keep your tanks full then carry on. Mine are generally around 1/4 full by the end of the season and remain that way right through Winter until first fill in March. I doubt next March there will be anything noticeable gathering in the separator bowl of my polishing rig. Each tank holds 400 lts, so if there was anything to the theory then these would definitely be proving it.
I do keep my filler caps thoroughly greased.
PaulRainbow
Well-Known Member
So just random and meaningless number then ?
Yes, other threads have also contained random and meaningless claims. This one actually contains some real World data that suggests otherwise though.
My own random and possibly meaningless feeling is that the possibility exists, so it can't hurt to keep the tanks full. I have never used fuel treatments, don't have any fuel polishing equipment (although i have considered it from time to time) and have never had fuel problems <touch wood>.
superheat6k
Well-Known Member
You do like sniping and trolling don't you, getting quite a reputation for it I see.
If you don't like what posters on here have to say then that is fine, but surprisingly some of the responses on here are based upon experience, training and qualifications, so having facts and figures long ago forgotten might not be so relevant when this is balanced against the poster's providence in this regard.
PaulRainbow
Well-Known Member
If that's what you call challenging those who post random figures and claims as if they are fact, then yes.
Excellent.
Indeed, and those people seem to be posting in this thread to verify that condensation in fuel tanks is real.
rogerthebodger
Well-Known Member
Paul This has taken me back to my uni days
The easiest way to work out if condensation will occur is to look at a psychrometric chart which relates the air temperature relative humidity and the dew point temperature ( temperature at which point water will condense). In a tank this will be the temperature of the inside surface of the tank.
From this chart if the tank inside air temperature is 10 C and the relative humidity id say 60 % the temperature of the inside surface of the tank must be 5 C or lower for condensation to occur.
On a metal tank this could be the temperature inside the boat but a plastic tank with a much lower heat transfer coefficient the inside temp of the boat would need to be lower.
Put your own figures into the chart and see what you get.
The other point is that if condensation does take place the RH inside the tank will lower unless there is an inflow of humid air. Now with the normal tank arrangement there can only be in inflow of air if there is an outflow of fuel. This will only occur when the engine is running in normal circumstances.
I contend that during lay up time there cannot be much of any exchange of air so no or very little change in humidity. There could infact be a lowing of RH if the RH of the outside air is lower then the air inside the tank.
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lw395
Well-Known Member
Many boats have high levels of humidity at times.
Particularly when afloat, the bilge water can be at sea temp when air temp is lower.
If the vent is outside, well humidity in the 90's is common enough in Portsmouth, 2ft above the water it will frequently be 100%.
Water vapour is a gas. It will diffuse into the tank even without air movement. Through a small bore pipe of some length I'd guess it will be slow, but how slow?
A more complex problem than first meets the eye, but I'll put 'check filler o-rings' on my todo list instead.
Particularly when afloat, the bilge water can be at sea temp when air temp is lower.
If the vent is outside, well humidity in the 90's is common enough in Portsmouth, 2ft above the water it will frequently be 100%.
Water vapour is a gas. It will diffuse into the tank even without air movement. Through a small bore pipe of some length I'd guess it will be slow, but how slow?
A more complex problem than first meets the eye, but I'll put 'check filler o-rings' on my todo list instead.
sarabande
Well-Known Member
FWIW, I have a couple of 1000l diesel tanks on the farm. They are plastic (rotationally moulded) and spend a lot of their service life in a half empty state. We have quite chilly damp weather on Exmoor, and the tanks are in sunlight and tilted down towards the tap. The water trap from the tank consistently traps a good half a cupful of water each month. As far as I can see from experience, condensation does take place within the tanks, but I can't put a precise figure on the amount, beyond that 100 or so ml every month.
Given the range of temps and Rel Hum the tanks and contents are exposed to, there is going to be quite of lot of expansion both of the diesel and the air volume, and ambient air will be drawn in and pushed out; which is why the tank maker has installed a separate and quite bulky breather, as the big (6 inch dia) filler cap looks as if it make a firm hermetic seal against the threads.
And by goodness, the diesel contents get dosed with bug fluid !
Given the range of temps and Rel Hum the tanks and contents are exposed to, there is going to be quite of lot of expansion both of the diesel and the air volume, and ambient air will be drawn in and pushed out; which is why the tank maker has installed a separate and quite bulky breather, as the big (6 inch dia) filler cap looks as if it make a firm hermetic seal against the threads.
And by goodness, the diesel contents get dosed with bug fluid !
NormanB
Well-Known Member
Re - Rogershaw
... and just one smaller point in conditions of no fuel draw off, as the temp of the fuel tank increases (during the day) the tank will 'breath out' and as the temperature of the fuel drops (at night) the tank 'will breath in' and if conditions are right as shown in the RH charts above then as it breathes in it will bring in a fresh charge of moisture.
... and just one smaller point in conditions of no fuel draw off, as the temp of the fuel tank increases (during the day) the tank will 'breath out' and as the temperature of the fuel drops (at night) the tank 'will breath in' and if conditions are right as shown in the RH charts above then as it breathes in it will bring in a fresh charge of moisture.
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rogerthebodger
Well-Known Member
Fair comment but how much are we talking about.
The diesel will expand and contract based on the thermal coefficient of expansion but also the air will expand based on universal gas law P1 * V1 / T1 = P2 * V2 /T2 where P is a constant in this case.
The other issue is what is the major influence of this expansion. Is it the air temperature either inside the boat of the outside of the boat. Or will it be the sea water temperature difference.
In my case having steel tanks in a steel hull where the tanks are part of the hull and in the keel I would say the sea water temperature would have the major influence.
Guys lets have some real facts and true numbers.
NormanB
Well-Known Member
I did say it was a small point. ;-)
NormanS
Well-Known Member
Good, actual figures.
Given the amount collected from your two 1000 litre tanks, sitting outside and exposed to the full range of weather and temperature, I would think that with sensible precautions, those of us with modest boats with internal tanks, don't have too much to worry about. Sensible precautions means regularly removing whatever small quantity of water which has accumulated.
ghostlymoron
Well-Known Member
I'm glad you agree. The explanation I vaguely recall was backed up by gram moles and the like but conclusion was the same.
GHA
Well-Known Member
I hope it's nothing like the amount of condensation dripping from my hatches when the temps are right....
ghostlymoron
Well-Known Member
Best way to avoid that is stop breathing.
GHA
Well-Known Member
On my steel boat, in the engine bay under the cockpit sole where there's no sprayed insulation itnwill be dripping as well. Like someone's been round with a spray gun.
Piers
Well-Known Member
Hi everyone. May I speak from experience? I've been involved in boating for almost 30 years some of which has been involved as 'staff' on Motor Boats Monthly cruise in company adventures.
I've seen too many boats have issues when seas become emotional, just the time when you want your engines to work. Far too many occasions are traced to blocked fuel filters, blocked from diesel bug and or water. Why? Emotional seas stir up the rubbish at the base of the tanks. In most cases, the owners have admitted not knowing about 'fuel etiquette'. For too long they've not treated their fuel and they've not thought about water ingress.
So, my belief is simple. Not wanting engines to fail when I need them the most, look after the fuel. Change filler O rings regularly. Check the bottom of your tanks regularly to see what's there. Treat the fuel, carry many spare filters, and know how to change them.
It's when things go wrong that you need your fuel to be clean.
I've seen too many boats have issues when seas become emotional, just the time when you want your engines to work. Far too many occasions are traced to blocked fuel filters, blocked from diesel bug and or water. Why? Emotional seas stir up the rubbish at the base of the tanks. In most cases, the owners have admitted not knowing about 'fuel etiquette'. For too long they've not treated their fuel and they've not thought about water ingress.
So, my belief is simple. Not wanting engines to fail when I need them the most, look after the fuel. Change filler O rings regularly. Check the bottom of your tanks regularly to see what's there. Treat the fuel, carry many spare filters, and know how to change them.
It's when things go wrong that you need your fuel to be clean.
Pete7
Well-Known Member
The DSM 300 drives the echo sounder transducer for a C series chart plotter plotter. Gave a good picture but was bloody expensive so sold it and went with a simple Garmin plotter when switching from Rib to yacht.
