Water tank suction with clear vent?

[Dan_Y]

Was using Peggy's approach to treating my 75gal fresh water tank in our h36 due to stinky water coming from hot water tank. Opened all faucets to drain the full tank with my 2.9 gal/min pump. Air whistled around the tank filler cap when I removed it to refill maybe less than a minute after running the tank dry. I can get at the tank hoses (both ends - thanks HM) so I removed the vent hose from the tank end and could blow through it and out the vent with a little resistance, but my breath would flow out in 2-3 sec. Didn't try suction though ..doh. The vent looks like this:
http://shop.hunterowners.com/hp/part.php?m=36&c=8&p=53350. I assume they don't vent too rapidly since they are a fuel vent.
I blasted water at the vent from the outside before disconnecting the vent hose. Also, a small dribble of water came out of the vent when over filling the tank initially, but the vent hose has a loop up right after the vent that effectively makes the vent about 8-inches higher than the filler port even though the filler and vent are at about the same height. Didn't want to pressurize or stress the plastic tank by sealing the dock water hose to the filler port to blow out the port. We have mega pressure at the dock.

Any ideas why the suction in the tank with what seems like a clear vent? Doesn't seem possible. Maybe this style vent is really small and the tank was still venting?
Tanks-a-lot...
Edit: Actual flow rate is 2.9 gal/min (Jabsco PARMax 2.9). My apologies for incorrect info.

 

[JamesG161]

Opened all faucets to drain the full tank with my 4.3 gal/min pump.

Sounds like your pump is bigger than the original pump size (guessing). What is the capacity of the water tank?

BTW a standard landlubber shower is ≈2 gpm and my OEM water pump is max rated at 2.5 gpm.

The vent looks like this

First time I had seen that vent fitting. Is it a "one way" flow vent?

the vent about 8-inches higher than the filler port

Not sure why that higher vent loop is needed, but if you fill rate is fast then that would be no biggie. If that bothers you, fill the tank at a slower rate. To me it would be a confirmation of vent open.

The normal function of a boat tank vent is to allow air to flow in as liquid flows out.

Bottom line is your vent must flow 4.3 gal/min of air into the tank.
Jim...

PS: Air vents OUT when the deck fill caps are open for normal ( not mega pressure /flows).

 

[thinwater]

No, that is not right. 4 gpm is low in terms of venting capacity. A 5-gallon Jerry can drains about like that through a tiny vent.

The vent type is generally used to keep following waves out of a fuel vent. Likewise the high loop is to keep seawater out of the water tank.

Many boats terminate the vent inside the boat, but if you over fill the tank that is bad. Some take it to the sink for that reason.

Could the hose be kinked? Either that or dirt in the vent, possibly insects.

I would replace it with a conventional mushroom through hull and add an inline strainer to keep the bugs out of the tank. The high loop should keep seawater out of the tank. Easier to maintain.

 

[JamesG161]

Likewise the high loop is to keep seawater out of the water tank.

Ahhh that makes sense. I have no idea about his vent line sizing but if you pump out 4.3 gpm of water, and he apparently pulled a small vacuum on his tank...

My 60 gallon tank vent is under the FRP working rigging cover, no high point loop.
Jim...

PS: My 5 gallon Jerry can takes about 5 minutes to empty, not 1 minute. The flow of a landlubber 1/2" garden hose wide open, is ≈5 gpm.

 

[Peggie Hall HeadMistress]

Although it's a good idea to recommission the fresh water system annually, that won't cure a rotten egg smell from ONLY the hot water. That almost always means that it's time to replace the anode in the water heater tank if it's a glass lined tank that has one.

The anode is a magnesium rod, about 3/4" in diameter that is attached to the inside of the hot water "out" nipple, via a plastic coupling. It is electrically isolated from the fittings and from the tank. It extends all the way across the inside of the tank, stopping just short of the other side. There is an iron rod in the center of the magnesium that supports it, the iron being stronger than the magnesium. As the magnesium is eaten away and the iron rod exposed, there's a chemical reaction between the water, the iron and the magnesium that causes the "rotten egg" smell. Replacing the anode and flushing out the tank will usually make the foul smell go away.

Less expensive water heaters don't have a replaceable anode, they have anodized metal tanks You get the rotten smell when the anodozing wears off. The only cure is a new water heater.

As for the high arch in your water tank vent line...that's to keep any sea water that gets into the vent thru-hull from making it into the water tank. There should also be a high arch in your fuel tank vent line too, for the same reason. However, there should NOT be one in the waste tank vent line...it doesn't matter if a little sea water gets into it.

 

[Dan_Y]

Thanks for the thoughts and info. I'll double check the vent hose run and will disconnect the vent hose from the water tank again and try to flush both ways with dock water pressure and see what happens. I can see the vent end of the hose so it could, in theory, be replaced with a mushroom vent and bug strainer. Probably glued in place with 5200 though...

Peggy, good point about the anode. I'm sure that's the problem because it was cleaned 4 months ago and the sulfur smell started about two weeks ago. I'm bummed about the water heater now. It's a 5 gal Kuuma from 2008, so I guess it's about time for a new one. Kumma shipped the heater with a plastic drain valve for winterizing, but currently offers a magnesium anode option that replaces the drain valve to "extend the life of the water heater". It's less than $20 to boot, and fits their entire product line. Unfortunate that HM didn't include this little option. But they did include a thermostatic mixing valve!

While I'm bashing and praising HM, I was cleaning the strainer on the Jabsco PAR-MAX 2.9 fresh water pump before the final water tank refill, and saw a few drops of water coming from a seam on the pump assembly. The pump is mounted vertically on a wall under the galley sink, a little tough to get at. But HM oriented the motor _below the pump_, exactly the opposite of what the mounting instructions say to do. The drips appear to be flowing down on the outside of the motor case, but I'll remove, disassemble and clean to see if it fixes the leak. The leak must be on the input side because the pump does not cycle with all outlets closed. The rebuild kit I found is about 50 to 70% the price of a new pump...ha. It's a pretty inexpensive pump though. Stay tuned...

 

[Ron20324]

[QUOTE="..._below the pump_, exactly the opposite of what the mounting instructions say to do. ...[/QUOTE]

When I installed my washdown pump, I emailed Jabsco about mounting the pump upside down. They said it is okay, but leaks can run into the motor- if the motor housing leaks, too. I put it in that way to make the hose routing better. No problems, but then it does not get used all that often.

 

[Dan_Y]

Thanks for the info Ron. I'm sure that's why my pump is mounted that way as well, otherwise the input and output lines must cross instead of "in one side and out the other". I guess it's fine if I can stop the pump assembly from leaking. Dan

 

[Stu Jackson]

It's a 5 gal Kuuma from 2008

Kumma is a good heater, but it is a cheaper knockoff of the also inexpensive Seaward heaters. Next step up are the Isotherms, really good units, if you can fit them in and if you can afford them.

Your boat, your choice.