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Old 10-04-2016, 07:44 AM   #21
City: East Coast
Country: USA
Join Date: Dec 2013
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Originally Posted by JDCAVE View Post
Sure there is:
Attachment 57031

Let's say my finger represents the filler cap and the pipette represents the head of water in a filler tube that is inside the water tank, the surface of the water in the bucket represents the water level in the water tank at atmospheric pressure. The air space inside the pipette is under a vacuum that is released when I remove my finger. If the "O" ring gasket is a good seal, and there is a filler tube that goes inside the tank, you can theoretically get a vacuum, even though the vent lines are functional and at atmospheric pressure.

The vent lines are functional.
Why would there be a filler tube inside the tank? If this was the case, everyone with that style of tank would have the same problem you have.

How about this: Take the hose off the tank and reach in and see if there is a filler tube or it the fitting just connects to the tank. My guess is, there is no tube.

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Old 10-04-2016, 09:52 AM   #22
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City: Owings, Md
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I think your theory is correct, and agree with AusCan that if the fill was on the side of the tank, you would have the same affect as a diptube when the water level is above the inlet fitting. Or maybe someone added a diptube for no good reason, either way it doesn't hurt a thing as long as your vent is working and your pumps are not struggling against a vacuum.

I experience the opposite effect with engine oil dipsticks. Dipsticks with a tube that protrudes deep into the pan and have a tight seal at the top (little yanmars) will trap air in the tube after the motor shuts down and the oil level in the pan rises back up, when you first pull the dipstick it looks like there is very little oil but if you re-stick it, the level is just fine.

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Old 10-04-2016, 12:51 PM   #23
City: Melbourne, FL
Country: USA
Join Date: Dec 2014
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If you have problems with bugs clogging vents, add a sintered bronze plug to the line(s).

They come in all sizes and are porous enough to vent the line but no visible holes big enough for a bug.

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Old 10-10-2016, 12:12 PM   #24
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City: Lions Bay, BC
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Vessel Name: Phoenix Hunter
Vessel Model: Kadey Krogen 42 (1985)
Join Date: Apr 2011
Posts: 1,199
We went to the boat on Saturday and I checked the vent lines again. I can access the starboard vent line at the tank and can confirm that the vent line is open through to the through hull: I can blow air through the vent line. However, I can also confirm that WesK is correct: There is no down tube into the tank that could account for the release of the vacuum when I open the filler cap. I can also now blow air from the ventline opening and out the filler opening. So...I'm thoroughly confused! I cannot identify any kinks or airlocks in the vent-line or filler line on the starboard side, no standing water etc. I will add "replace vent lines with braided hose" to the "To-Do" list. Is there any need to put a "barbers loop" in the vent line?


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