check valves for vent line on auto ballast

I recently installed a ballast system for a buddy. Everything works great, except the vent lines continue to vent after the pump is turned off. My buddy would like to be able to fill the sacs so that they are more full. What is the best solution?

I used brass check valves that just have a flapper that hinges, should I use one that requires more pressure to open up or just put in ball valves so that he can overfill the sacs?

He thinks he has lost about 200-300 lbs in the boat because he can't fill the sacs as full.

are the vents at all times above the top of the water level in the sacks when full? if they're not, the sacks will drain until they are.

This is a problem that is common with sacs as opposed to hard tanks. When the sacs reach their "full" potential and are buldging, the pressure forces the water out the vent line. Unfortunately, water will continue to run out the vent line until the pressure in the sac is at a point to where it stops pushing water out the vent line.

I had the same issue with my SSV (before I upgraded to larger sacs). To keep every drop of water in the sacs I installed ball valves on the vent (drain) hoses just before the through hull fitting that spits the water out the side of the boat. When the sacs get full and start to spit water out I turn off the fill switch and then quickly close the valve on each line.

This worked out really well. The only downside to this solution is, if your vent line and drain line are one in the same, you had better darn sure remember to open the valves before you start to empty the sacs!

As I mentioned before, I recently upgraded my sacs. Since my new sacs are so freakin' huge, they never get to the point where the pressure is spitting out the water. If I let them fill that much the lids of my compartments would fully close.

So, you can either get larger sacs that don't need to be filled up all the way or you can install valves on each vent/drain line.

are you saying hard tanks wouldn't do this? any internal pressure that's higher than the head pressure in the vent line will cause them to spit out the vents. hard tanks would be the same or possibly even worse because they can't expand like (coverless) sacks.

but, putting a shutoff valve in the vent line would definitely allow you to fill sacks more.

Of course hard tanks do this, but not to the same degree. Hard tanks do not expand past their dimensions, sacs do. Lets say you have a hard tank that is 10x10x20. When it fills all the way up it is going to spit out water for a short period and then stop, but basically the water level inside is damn near close to 100% capacity.

Let's say you have a sac that is 10x10x20. When the sac fills all the way up it is going to buldge, unlike the hard tank. The sac may buldge to where it is more like a 15x15x25 sac. This is because the material of the sac will stretch. A hard tank will not stretch. The pressure in the sac will cause the water to spit out until the pressure has reached a level where it can no longer force water out. Now the sac has shrunk to around 12x12x22.

I'm not going to do the exact calculations here, but basically when the sac is buldging completely full it may be perhaps 125% full, past it's original dimensions. However, when the pressure spits out the water it may be only 110% full, past it's original dimensions

I think what Gordan was wanting here is a way to keep the sac 125% full at the 15x15x25 mark. Adding the valves will do this.

(Message edited by nauty on June 15, 2005)

gordon check mcmaster carr at mcmaster.com i got my valves there for my system. they have every size and every valve you can imagine.

oh yeah i used plastic barbed, ball valves

here is pic of the check valves I used and their location

Gordon,

What kind of fittings are you using to connect the hose to the sac? Those look like they may work a little better than what I am using.

Also, what type of clamp is that you are using to hold the hose to these fittings? Is it plastic? Where did you find them?

the clamp is plastic, I am not sure where it came from, it was on the aerator pumps that came with the boat(we upgraded from semi auto to auto)
The fittings I used are just plastic barbed fittings from Menards, on my ballast system I do not even use clamps on the sac the fittings are that tight!

Gordon,

Is there another thread w/ more details on your install? If not I'd love too see more and some more pics. I wan't to do a similar install and I have don't have a vdrive so I'll have to let the sacs sit on the floor like yours.

thx

Q: Why have a vent?

Why not just have a reversible pump that pumps in/out the same hole in the bottom of the boat?

Don't people vent in case they over fill the sacs? Obviously in this install it wouldn't be as big of a deal but I saw a pic a while back where someone broke the fiberglass around the v-drive by over filling a sac.

yes, the vent is to help prevent overfilling, you wouldnt think it would be a big deal where you can see them but it does and will happen, fortunately I have not had one blow yet(I did not vent my own ballast system.) I know for a fact that my buddy can get distracted pretty easy so we wanted an extra safety feature, and eventually he is putting them in boxes so you wont be able to see them.

as far as a write up on the install we have not done one yet, but it is pretty basic 4 pump 4 bag system, 4 simer pumps and 4 bags!

we use a air release float in irrigation which works great to remove all air..what it does is you mount it at the highest place on your sac..when the water reaches the float ball it rises and seals water from going out..just releasing the air...i could get the name of the item for you

Ryan,

Yes, please post up the name. These sound very interesting. It's always a beating having to burp the sacs. If you can let us know where you found them that would be great too.

Thanks,

Richard

Overfilling can be a problem because of the pressure the sack can place on the structure surrounding it. Didn't Supra have a problem with cracking caused by an overfilled sack? It seems to me a vent is critical to prevent this. If you put a check in the vent line, it should allow water to pass through.

Gordon:
When I installed my system I had close to the same problem. Mine didnt drain all the time, but the sac would not get a full as I liked with the flapper. The flapper also gets corrosion,and sticks. then it is like having no check valve.
I replaced mine with a 1" plastic check valve from Home depot, and it works fine now. Fills full, and no problems.

mike, was it rated for a certain PSI? I saw those but i was afraid that there wouldnt be enough pressure to open up the valves...