Passive Draining or Siphoning?

[Vicseek]

Recently installed an Enzo Sac in the Rear Port side Locker. It was a simple installation replacing the existing 350# bag. After reading some threads and observing the previous sac not remaining full during surfing I installed a simple Ball valve prior to the thru hull "vent" opening.
After filling the entire bag and observing the water coming out of the vent and a trickle out of the drain as well I shut off the pump and closed the ball valve hopefully locking the bag permanently in its full state.
After only 20 or 30 min I noticed somehow the bag had lost 1/4 of its contents.
the Diagram below is my understanding of the ballast system, it's not complete since I couldn't really get a good look at where each fitting connects to either the hard tank, pumps, or vents. In my RZ2 the vent line seems to be T'd off to another line which seems to maybe run across to the other "starboard" side vent?
Hoping somebody can finish my diagram or shed some more light on how I can lock in the full 1200# of water for surfing.

Ballast Dia.jpg

When the bag is completely full I see water coming out of the Vent hole and a trickle coming out of the drain hole. This makes sense since I suppose the weight of the water plus full bag plus ballast pump continually pumping in more water will actually push past the drain pump and up and over out of the drain. But...will normal ops "surfing" keep pushing water past the drain pump? If so, what good would a one way check valve from "wake makers" do on the drain line to stop this?

[Iwndr]

I won't get to test mine for another three weeks or so but I was experiencing that issue last year with a 400# sac over my 250# hard tank. This year I pulled the hard tank and V-drive sac on the port side and replaced with a 1200# Enzo sac also. I plumbed the drain and vent lines to the opposite sides and installed a check valve on the Fill line. I think that is where my passive draining was occurring.

[Tault145]

I've had the same problem with a different set-up. If you put a one way valve in between the intake and the bags you should be all set!

[Wakeman22]

I've had the same problem with a different set-up. If you put a one way valve in between the intake and the bags you should be all set!

X2 Check valve.

I had the similar issue.

[chpthril]

Here is some info on the Plug-n-Play passive draining. This can also be an bump in the road with any ballast upgrade when tall/large sacs are used.

http://www.tigeowners.com/forum/showthread.php?t=17025

I think most of the passive draining is through the drain pump. These pumps are vain style pumps, so there is no actual contact between the veins and the pump body, unlike an impeller pump. This means water is free to flow through the bump under its own power, if the conditions are right. If the filled sac is higher then the drain t-hull, then this would allow the water to drain out as gravity and the weight of the water would allow the water to level. In this setup, its obvious that the t-hull is below the water level when the sac is filled, so passive draining will happen.

There is some passive draining through the vent, but a little back pressure from a check-valve seems to stop this. It take pump pressure to open the valve, so once the pump is cycled off, the valve closes and holds back the water.

This same principle may work in the drain line, but I haven't tested it. Using a c/v requiring a little pressure to open, when the pump is on, just may hold the passive draining at bay.

IMO, I think the most effective and simplest mods to combat the passive draining is to cross the vent and drain lines across the boat. Just swap them with the other side. Only requires some additional hose, 4 barb x barb hose connectors and clamps.

Some may experience some passive draining through the fill plumbing. For this, a check-valve in the fill line is a easy fix. But, I would try to rework the hose routing first. The gunwale height of most Tiges is such that in many cases, you can get the fill hose routed up higher then the sac as it comes out of the bilge, then taking a down-turn toward the sac. This high spot in the plumbing creates enough up hill climb, that the water pressure is not enough to make it up and over. When the fill pump is shut off, the remaining water drains down too the sac and this breaks any siphon effect also. If rerouting is not going too work due to the filled height of the sac and layout of the hose and boat, then install and check-valve. With the right one, there will be little reduction in flow.

[Duncan]

Our 2009 RZ2 has the stock 250s and 1k Custom sacks, all plumbed separate. Auto-siphon was an issue from day one.

First, I put in riser loops on all lines. Still drained. Second, I routed the vents to the opposite side. Still drained. Third, this winter, I routed the drain lines to the opposite side. This has not yet been tested. If it still drains, the only possibility is the existing check valve in the fill line is not sufficient to hold the water.

I summary, I agree with ChpThril -- first, route your vents and drains to opposite sides (there is no way these lines can drain in this config under surf ballast).

In the above diagram, my bet is siphoning out the 250 drain line, which pulls from the Enzo. If not, then the fill line valve is missing or insufficient.