Hello all, posting again after working overseas for a bit. Hope you are all well etc. First of all thank you for taking time to read this, it may be slightly long winded.

I made my split mould for a large diameter tube. The mould is 300mm id x 400 od x 1500mm long. So far I have attempted to bag the layup, sealing on the on the inner mould surface. Of course this was useless because of the splits.
The next attempt was to envelope bag, I couldn't get a vacuum probably due to the bag piercing on the mould exterior.
So the next thing I was going to try was breather clothing the exterior and envelope bagging, until it dawned on me that the resin is going to migrate through the splits into the breather and make a right old mess.
So what are my options? I have considered silicon sealing the splits on the exterior and proceeding with the envelope in an attempt to stem the flow of resin into the breather. Or I could perhaps resin up the exterior and attempt to seal the bag on the interior again, basically seal the splits and treat it as a large panel type bagging.
Any thoughts on the best option going forward in an attempt to get this part complete. The second option is preferred as it will simplify bagging greatly (this is heavy and enveloping is difficult). I realise there is probably no right or wrong answer as such, however any input from you experienced moulders would be greatly appreciated. Pictures to follow:

Becoming a much debated topic on here haha.

For me, I clamp the vacuum side as soon as the resin has completely wet out the stack (I try to include the brake zone in this, though sometimes with especially large brake zones it just won't happen). Then for cosmetic parts, clamp the resin feed a short time after, which all depends on how big your part is. 

My theory is, leaving the vacuum on is pointless once the resin has wet out the laminate. It can't be any safer than clamping and turning the pump off, if your part develops a leak post-infusion then having the vacuum active and connected still can't save it. Reason being, the air would now have to move through the resin in order to be evacuated. For one, air doesn't like to move through the resin, it will likely get trapped en route regardless. Most importantly, your resin is going to gel at some point. Air won't be able to move through it anymore, but it will still be able to move into the bag and reduce your compaction. Unless you have a way of maintaining a path for the air to move directly from the point of leakage to the vacuum connector, then it isn't going to. Your pump will simply maintain full vacuum right at the connector, and not within the whole bag.

Now this is really just addressing the concern of air leaks during infusion. If you dont have a leak before the infusion starts, then it is very rare to develop one afterwards. So it isn't normally a problem. Vapour control and outgassing is another matter. My above advice really only pertains to infusing with epoxy. Generally epoxies are 100% solids, and unless the hardeners are very old and have absorbed moisture, they normally don't outgas very much if at all - atleast not enough to worry about with an infusion.

Vinyl esters and polyesters on the other hand are a different story, and here is where I can see why leaving the vacuum active and connected would be beneficial. If you clamped as soon as the infusion finished with these resins, then they continue to outgas a lot until they cure, which can cause all the same issues as an air leak. Then after they have gelled, yes you lose the effectiveness of the active vacuum again for all the same reasons as above, but the volatiles coming out of the resin are also much less than they were, so there is a benefit.