Fat sac hosing, how will water flow question?

Below you can see my crappy diagram.

If I have a pump, pumping through a y splitter to two fat sac with equal length hosing going to each sac. Both fat sacs should receive water at an equal rate. The key here is that one sac is bigger than the other.

Once the 400lb fat sac is full what will happen?
A. Water will go out the vent hose, and at the same time the other half of the water will continue filling up the 500lb fat sac.

B. Water will stop going into the 400lb sac and all of the water will go into the un-full 500lb sac untill it is full.

If A. is what will happen, then, when the water goes down the vent hose and reaches the Y splitter, will it:
C: Go to the one way valve and out of the boat.

D: Instead of pushing the one way valve open, will it go down the vent hose of the 500lb fac sac and assist filling it up.

At some point will both sacs be full and both have water going through the one way valve and out of the boat?

Finally, when reversing the pump since it will be a closed system, when the smaller 400lb sac is empty will the pump be able to continue emptying the 500lb sac? I would assume so.

Water flows downhill unless there is a siphon in play. Be careful of pressures without vents, 2psi (about like a balloon) on a typical fatsack (60x10") will exert about 1200 pounds of force on your boat. I would recommend running seperate pumps for fill/drain on each bag, 4 total, aerators make sure the fill pumps are below waterline and the drain pumps are at the lowest place on the sack. You don't need the one way if you use loops and siphon breaking vents, see my crappy diagram.

I am going to use one reversible jabsco water puppy instead of aearator pumps. I have tested it out and it can easily drain the bag through 15 feet of hose that goes up and down.

I will have a vent/overflow hose on both of my bags so that I know when they are full. I am just unsure about how they will fill and overflow.

I dont think it would be possible to bust either bag with my planned setup because if one bag was full it should go out the vent hose and either into the other bag or out into the lake.

Looks like you have the vent/pressure covered. The water should flow into the lowest point first all the way to the highest point where you should have your vent.

How well will the Jabsco water puppy handle the Y splitter to fill two sacs and drain two sacs? I know it will take twice as long, but it takes me at least 10-15 minutes to get to my good wakeboard spot.

And then coming out of the two sacs for the vents will be water hoses, they will conbine through a Y splitter into one hose near the back of the boat, and then going out into the air from the side of my boat.

When both sacs are full and both pushing water out the vent hoses and they come to the Y and you have two hoses of water combining into one hose of water, what will happen?

Will it just spew faster and farther out of the boat or will it bust one or both of the sacs?

Most likely as soon as any water comes out I will turn off the pumps anyways cause the sacs will be full enough for me.

I've got Y splitters all over my system with one Jabsco. I fill 4 large bags (2 600's, 1 550, one 350).

I put a ball valve near the end of each line connected to each bag so I can control the flow. I turn them off when the bag is full to ensure no overfilling.

You use the ball valves and watch the bags as opposed to the vent setup? I know that I would get distracted and would forget to close off one and it would bust.

My system is virtually the same as the one described last year if you search for "semi-automatic ballast system". Many of these systems do not have overflow. All my bags are where I can see them except for the locker sac, and when it starts getting full the door to the locker starts popping up, so it's easy to see. I've never had a problem. When you empty, the bags get vaccumed so there's no air in the system to speak of.

me too.

I had a similar setup on my old boat. One reversible self priming pump and three sacs. I had ball valves on the inputs to all sacs. As said before, you can turn off the valve to one sac as soon as it is full. You can also regulate the flow to each bag so that they all finish filling at about the same time. No problem with draining. It will suck one sac flat and then finish draining the other one. I did not have overflow valves on mine.

Even with overflow valves, you still have to be careful. You can still build up considerable pressure on the bag. The water will not flow out of the bag as fast as it flows in. The bag will continue to expand.

Matt, if you're using a reversible system, yes. If aerators, then your drain and overflow are the same. so i guess you could leave your fill pumps running all day if you really wanted to

How do the professionally set up ballast system like the moomba bag ballast work to keep from busting?

Do I need to have a vent hose and a splitoff right before the sack to keep from busting it?

My goal is to be able to flip a switch and fill two bags. Then I'll look back and see water pouring out the thru hull in the side of the boat and flip off the pump.

I have not done it, but I think you just need to plumb the outbound line such that it can carry as much water out as comes into the bag for overflow (hopefully more). Then make sure you have a check valve on the outbound line so that when you drain, you don't suck air into the system and loose the prime on your pump.