will a sealed bag tank work with flow/return system?

[martynwilley]

hi,
i just finished my boat and went to launch it today, the motor ran and started fine, but shortly after getting it off the trailer the revs increased and then cyt out. i have taken the fuel delivery pipe off the motor and started the fuel pump, it is not a constant flow (it starts then stops)

i have my fuel rigged as follows- bladder tank to input on water seperator, output on water seperator to inlet on pump, pump to inlet on engine, return from engine to spare inlet on water seperator. (the pump is a bosch high pressure)

the bladder tank is sealed, i have tried pushing all the air out of the tank and screwing the cap back on as to try get all the air out but im still not getting a constant flow.

i will check all the lines and clips in the morning for any signs of leaks but its all brand new hose and fittings.

iv been over and over in my head how this is supposed to work and how an air pocket in this flow/return system is to escape (usually it would go back into the vented tank i assume and out thru the tank breather) does anyone else on here run a bladder tank on a flow/return efi system?

any help would be much appriciated.

thanks Martyn

[RossM]

I think you will have to run a low pressure pump between bladder tank to the water seperator

[martynwilley]

I have a primer bulb between the bag tank and the water separator already, could replace this with a Holley low pressure pump but that's just another pump and relay that could potentially fail, is there no1 out there running a similar set up?

[martynwilley]

After careful deliberation and a few replys. where in my system does the air vent to? There are No breathers anywhere and the pick up for the bag relies on there being No air in it as there is No pick up pipe in it, it draws from the top of the bag.
Sorry if it seams I am going round in circles but just can't figure out how to get the air out!

[Renegade]

I think it would need pumping back. its quite a vacuum caused when emptying.

[OCRDA]

I have used a bag on both 2.5 EFI and the V8 OMC 2 stroke @ 9000 rpm simply fed the return back into the cap of the tank. Just be sure to bleed any air from tank first.

Bob

[martynwilley]

Thanks Bob, when you say you had the return back to the filler did you drill the cap in the hexagonal recess and tap a tail end union into it? If so how did you fit and remove the cap after as it would No longer be possible to use the hex key? And what is the best method of 'bleeding' the air out the tank?

[OCRDA]

Yes I put a fitting in the hex and fit hand tight !! Keep pressure on tank to expel air when fitting cap !!