Figuring out how water flows between my tanks

[LifesBetterWhenYoureBeating]

Yeah, it's me again with another water-related question

This time I'm trying to figure out how water can flow between my two tanks. I drew the attached diagram to try and figure everything out but there are a couple things which are not clear to me:

* With v1 and v2 open, if I run the water pump, would it have the same effect as priming a siphon and thus cause the tank levels to equalize?

* With v2 closed, if I accidentally overfill T1, would water flow to T2 via the vent hose, thus leaving it filled with water and no longer effective as a vent?

Thanks in advance!

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[garyfdl]

Based on your drawing:

Opening V1 and V2 effectively cross-connects your two tanks. In this case, the pump should draw from both tanks more or less equally (assuming no line restriction or major disparity in line length). There is no siphon per se.

I'm not sure how to answer/don't understand the second question relative to the drawing. IMO the faucet should not be connected to the vent. The vent should be independent, and the faucet connected to the discharge/pressure side of the pump. But generally speaking if the two tanks have a common vent line, then it is possible that it will cross connect the tanks, and if one tank is overfilled, water will flow to the other tank.

[LifesBetterWhenYoureBeating]

Originally Posted by garyfdl

Based on your drawing:

Opening V1 and V2 effectively cross-connects your two tanks. In this case, the pump should draw from both tanks more or less equally (assuming no line restriction or major disparity in line length). There is no siphon per se.

By cross connects you mean the water will flow freely between them (until they're equalized) if the water level is higher on one than the other? I was wondering if there are any preconditions for that to happen, like the whole extension of the hose being filled with water, that's why I thought maybe the equalization would only start after I ran the water pump

I'm not sure how to answer/don't understand the second question relative to the drawing. IMO the faucet should not be connected to the vent. The vent should be independent, and the faucet connected to the discharge/pressure side of the pump. But generally speaking if the two tanks have a common vent line, then it is possible that it will cross connect the tanks, and if one tank is overfilled, water will flow to the other tank.

That faucet is only connected to the vent lines of both tanks. There are other faucets connected to the manual/automatic pumps

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[s/v Jedi]

Yes, you create a syphon by overfilling.

I am assuming you have two pumps, like me, and the best system I could engineer is like in the picture.

Note: the pumps have a one-way valve that prevents the syphon where their outputs interconnect.

This manifold allows one pump to pump from either tank.

[LifesBetterWhenYoureBeating]

Originally Posted by s/v Jedi

Yes, you create a syphon by overfilling.



I am assuming you have two pumps, like me, and the best system I could engineer is like in the picture.



Note: the pumps have a one-way valve that prevents the syphon where their outputs interconnect.



This manifold allows one pump to pump from either tank.

You mean the siphon is only created via the vent lines when overfilling? No siphon via the regular supply lines when both valves are open?

I have only one automatic pump. The other is the foot pump

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[Bill O]

Based on your sketch, the tanks are separate and it doesn't appear they will passively equalize the water levels between the two tanks.

The isolated tanks aren't a bad thing. Separate tanks are good if one side is contaminated or springs a leak, then you don't loose all your water.

Downside is if you boat is sensitive to weight (one tank full, the other empty). The easy fix is to switch tanks (valves) to equalize them through usage.

[garyfdl]

Originally Posted by LifesBetterWhenYoureBeating

By cross connects you mean the water will flow freely between them (until they're equalized) if the water level is higher on one than the other? I was wondering if there are any preconditions for that to happen, like the whole extension of the hose being filled with water, that's why I thought maybe the equalization would only start after I ran the water pump

Yes. Cross-connect(ed) means the tanks act as one. Levels in the tank should be/or can equalize. There are no 'preconditions' as such, but... when you fill, the tank you're filling will fill up first. The levels won't necessarily rise equally. The 'downstream' tank will usually lag behind the one the water is going into first. Running the pump shouldn't be necessary.

BUT...

This is based on what your schematic shows. We are talking about tanks located port & starboard. That means there might be check valves in the lines going to the pump, that prevent water flowing freely between the tanks. This is so you can't overfill while heeled.

Originally Posted by LifesBetterWhenYoureBeating

That faucet is only connected to the vent lines of both tanks. There are other faucets connected to the manual/automatic pumps

That's interesting, and quite a nice feature actually. It functions as a 'vent valve' and tells you that the tanks are full. It should also negate overfilling the leeward tank and spilling water into the bilge.

[garyfdl]

Originally Posted by LifesBetterWhenYoureBeating

You mean the siphon is only created via the vent lines when overfilling? No siphon via the regular supply lines when both valves are open?

Originally Posted by s/v Jedi

Yes, you create a syphon by overfilling.

OK you guys lost me.

• What do you mean by siphon/syphon (and yes I know what a siphon is) how do you create this condition by overfilling, and where is the siphoned fluid going?

[LifesBetterWhenYoureBeating]

Originally Posted by garyfdl

OK you guys lost me.

• What do you mean by siphon/syphon (and yes I know what a siphon is) how do you create this condition by overfilling, and where is the siphoned fluid going?

My understanding is that with v2 closed the overflow from T1 will be pushed through the vent hose to T2. Once T2 is full the overflow comes out the vent faucet and I get angry with myself because I'll have to suck all the water from the vent hose. I guess that's not a siphon effect, though

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[garyfdl]

Originally Posted by LifesBetterWhenYoureBeating

My understanding is that with v2 closed the overflow from T1 will be pushed through the vent hose to T2. Once T2 is full the overflow comes out the vent faucet and I get angry with myself because I'll have to suck all the water from the vent hose. I guess that's not a siphon effect, though

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OK thanks, and technically no, that's not a siphon.

When that happens can't you just open V2 and let the tanks equalize. If that fails to clear the vent, I would think running the/a pump would drop the level in the tank(s) and clear the line.

[LifesBetterWhenYoureBeating]

Originally Posted by garyfdl

OK thanks, and technically no, that's not a siphon.



When that happens can't you just open V2 and let the tanks equalize. If that fails to clear the vent, I would think running the/a pump would drop the level in the tank(s) and clear the line (and that would be a siphon).

Unfortunately not because the vent hose makes a U shape (to pass under the floorboards) on its way to the faucet. I forgot to draw that on the sketch

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[garyfdl]

Originally Posted by LifesBetterWhenYoureBeating

Unfortunately not because the vent hose makes a U shape (to pass under the floorboards) on its way to the faucet. I forgot to draw that on the sketch

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Mmmm, even if there is a 'U' in the line, if the line is full, and you draw it down from the tank side, it should siphon most of the fluid back. Admittedly some would remain in the 'U', but I don't think it would effect anything. Might make gurgling noises when water is being used.

[LifesBetterWhenYoureBeating]

Originally Posted by garyfdl

Mmmm, even if there is a 'U' in the line, if the line is full, and you draw it down from the tank side, it should siphon most of the fluid back. Admittedly some would remain in the 'U', but I don't think it would effect anything. Might make gurgling noises when water is being used.

In practice it did affect the venting of the stbd tank - - the one whose vent hose is U shaped. It's a SS tank and when I bought the boat every time I drew from it it'd make loud bangs. That stopped only after I sucked the water from the hose

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[garyfdl]

Originally Posted by LifesBetterWhenYoureBeating

In practice it did affect the venting of the stbd tank - - the one whose vent hose is U shaped. It's a SS tank and when I bought the boat every time I drew from it it'd make loud bangs. That stopped only after I sucked the water from the hose

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That 'U' must be pretty big. The banging is (probably) the sides/top/bottom flexing due to the blocked vent. I'm surprised it would occur if V1 and V2 are both open.

[s/v Jedi]

I took the “syphon” word as a common expression for water moving from one tank to the other. There are multiple ways to see this happen with this diagram:

- when one tank is overfilled, the water will run via the vent line to the other tank. Only when that one is full too, will the water run into the sink.

- when both valves are open, both pumps are primed but not in use, you get a syphon via the valves when one tank is filled more than the other, or when the boat heels.

You can use the manifold I showed earlier because the foot pump has a one way valve as well. This way you can set it up however you like by just turning a valve.

Note that there are 5 valves in the picture: one for each tank and one for each pump and the fifth for a cross connect.