I really like the idea of replacing the rear seat in my 97 Prostar with a custom seat/ballast set up. Assume I use a reversible pump and get a custom-made sac that fits the box I build. Here are my questions: <BR> <BR>- In some of the threads on this subject, I've seen people mention a vent hose. Would that be a requirement with a reversible pump system? My assumption would be no as long no air was introduced to the system. <BR>- Am I right in thinking the hose connections would have to be at the top of the sac? If they were at the bottom, it would seem the pump would have to deliver significant pressure to push all that water up into the sac. The only reason I'm even questioning this is that I've seen diagrams that show the connections at the bottom. <BR> <BR>Thanks.

A vent is a safety to prevent overfilling the sac and damaging your boat. The sac will expand and can break the seat structure, fiberglass compartment, etc. The impeller style reversible pumps have plenty of pressure to fill from the bottom of the bag.

each time you take the boat out of the lake, some water is going to drain out of the pump and the thru-hull. When you put it back in, a little column of air will be forced into the system. Over time it will build up and you need to burp the sacs.

These seem contradictory. The first says I need the vent to keep the sac from bursting. The second says I don't really need it but I'll need to burp the sacs on occasion if I don't have them.

In your statement you said you were assuming that no air would get introduced and I was pointing out how some air can get in the system. <BR> <BR>I don't know about bursting or not bursting.

YOU NEED A VENT ON YOUR SACK. Or you will break stuff. Or pop the sack, which is cool, you can hear it from outside the boat when you are in the water and your buddy hits the fill switch by accident when the sack is full. It's cool as long as your bilge pump works!

If you are using a fat sack and a reversible pump, connect the pump at the bottom of the sack,not the top, otherwise it won't empty properly. <BR>Regarding the vent, you will need one to ensure you don't pop your sack due to too much water pressure. My suggestion is you also add a check valve in the vent to allow air out, but not back in, that way the pump will suck the sack dry. Without a check valve, you find that the pump is sucking air rather than water out of the sack when it gets towards empty. <BR>If you are using a rigid tank rather than a sack, do not use a check valve as you won't be able to suck the water out unless air can get in to replace it