View Full Version : Need Gravity I upgrade help

04-19-2017, 01:20 PM
I'm upgrading my Gravity I system gradually on a budget. Starting by adding a 400lb locker bag, hopefully with only an additional drain pump for now and then maybe an additional fill pump for later.

Here's what I think the system is composed of now and what I think would be the minimum needed to add the bag. Am I thinking this through correctly? The existing fill pump would first fill the locker bag, then the locker bag would overflow to the existing hard tank. When draining the locker bag, the check valve should help suck all the water out and collapse it completely.

Anything I'm missing? Would this work?


04-19-2017, 06:22 PM
Which locker are you talking about? Is this a direct drive? Are your thinking of putting a bag behind the back seat In that locker, or the center ski locker? If the former - bad idea, you should not put that much weight back there as you can damage the fuel tank, fuel pickup and sender that is under the rear locker. Moomba warns against this. If the latter, and it's the center ski locker, then yes it would work, but with this cascading setup it going to take eons to fill.

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04-19-2017, 06:55 PM
Yeah, this will be for a direct drive. The existing 400lb hard tank is under the rear seat and this proposed setup adds the 400lb to the center ski locker ahead of the motor. I figured it would be slow (twice as long as current, that is), but I think I can at least put up with it for the short term before adding another fill pump.

Your mention of the cascading setup brings up another question... will the existing pump will be able to push water through the 1st bag and then to the tank OK, or should I tee off before the bag and let the water naturally split to each? Not that the flow capacity is any different, but I'm wondering if the way I have it diagrammed would be any more restrictive than putting a tee in right after the solenoid valve?

04-19-2017, 09:06 PM
Ok then. With that setup you will be safe. The check valve between the two will work as long as you have separate empty pumps. Only downside I have seen, as I had an 04 LS before my Craz is that you can overfill the center bag and pop the ski locker hatch, which is what you will do with that cascading setup, so it might be better to use the selectable T so you can fill each Independently.

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04-20-2017, 10:25 AM
Why mess around? Add another fill inlet and another pump and don't look back.


04-20-2017, 10:35 AM
I agree.

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04-20-2017, 01:52 PM
Yeah, it doesn't look like that much more cost once I delete some of the unneeded fittings associated with looping the old with new. Basically comes down to just the cost of the pump + a few more dollars.

Since the bag itself is the experiment, what I might do is test the new bag with the existing pumps, get the size and placement right, then get the additional pumps once that's all settled.

Thanks for the help, guys!

04-20-2017, 01:54 PM
I have an extra rule pump, that I took out of my old boat, if you are interested in it for a small fee. It still works perfectly. Just shoot me a PM if you want it

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