Thanks for the reply. Makes perfect sense. Do I use spiral tube for the vacuum circumference, as well as the inlet?

And also I have the spiral tube past both ends of the layup to guarantee the resin flows the full length of the layup. So the spiral is not sitting on the layup as such it is on the peel ply just prior to the cloth/core, and the connectors are half on and half off the layup. I seem to remember someone in the past saying the connector should sit flat on the layup?
Where exactly should i position the spiral to guarantee the whole lot gets wetted, is it OK to put them about one inch in from the ends?

You shouldn't need spiral on the vacuum side as well, you're going to have an even vacuum as it is. Really you use spiral on the vacuum side when you want to distribute the vacuum more evenly, so if you had an irregularly shaped mould that you knew was going to flow faster in one direction than another, you can use spiral tube to create a vacuum manifold that continues drawing the resin towards it rather than the flow sealing itself off and becoming choked. Because your geometry is very straight forward, your resin is going to flow very evenly out of the inlet spiral and straight down the tube. If you are envelope bagging, you will probably find the seams flow marginally faster than the rest of the tube, but I would still wager your flow front will get to the end of the tube all within about an inch of itself.

With connector positioning, you want to position everything off the laminate if possible, otherwise it will create a defect in the laminate. So unless you need to run spiral tubing on top of the laminate for some reason, again usually geometry related, then you keep it and the connector off the laminate.

I would say your biggest challenge will be the length of the infusion. 1500mm isn't an excessive distance for infusion, but after about 500mm the flow does slow a bit and at about 1000mm it can become a bit of a crawl. Which creates two issues:

1. You need to be aware of your pot life. Mix in 1kg batches rather than trying to do big batches of resin. Have the second batch mixed and ready almost as soon as you start the infusion, the first kg or two will flow very quickly. Once in the part your resin should continue to flow for atleast 3-4 hours, so its the resin in your pot that you need to avoid gelling or even getting hot before the infusion finishes. 

2. Keep an eye on your resin inlet during the infusion, and watch for slackness in the bag. Often if the resin is flowing over a large distance, the resin can sometimes flow into the bag faster than it can flow through the laminate, which leads to excessive pooling and slackness on the feed side of the bag. if you do notice it becoming slack, simply clamp the feed line for a minute or so and allow the resin to move through the laminate and even out again before you unclamp and continue as normal. 

To be honest, I doubt either of those will be too much of an issue if you are using a proper infusion epoxy. I would expect your infusion to take 40 minutes to an hour, so it won't be extremely long. But thought it worth mentioning anyway.

Thanks again for the valuable info Hanaldo. I will be using EC IN2 resin with 100% slow catalyst.
UPDATE: I have enveloped the tube and the results are promising:


The spiral and connector are off the laminate, could have done with a bit more mesh but looks ok.
Vacuum drop test:


After 30 minutes:


However I have clamped off the hose and get the same result, so the leak is at the catch pot / vacuum pump. In fact when I undid the clamp, the vacuum increased, so I think the envelope is good.
I just need to find the leak in the catch pot / vacuum pump and fingers crossed will be ready to infuse. I only did the gland on the catch pot hand tight, do these normally need a spannering? The 8mm id hose doesn't seem like a particulary tight fit on the barb connectors, i might trim the ends back a bit.

Thanks Lester, I had a feeling this might be the case as no air should be drawn into the resin. When should it be clamped off, as some people say leave the pump running through to cure, others say clamp it pre-cure?

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.

The clamping off versus leaving the pump on debate will run forever!

At the end of the day use whichever method works best for you. 

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

Thanks Hanaldo and everyone else that has contributed help on this thread and any others regarding this project. Today I managed to get the infusion completed successfully. The process took about an hour, and 4 kilos of resin, this was for a 1200mm x 300mm tube, 8x200g of laminate and 3mm of 3D Core. The flow went pretty much as you described Hanaldo, they were only out by a few inches each side. The air and resin bubbled through at the vacuum side and then the other side soon caught up, the brake worked out well. Going to leave it in the mould probably till next weekend to avoid any chance of distortion. Video of the final part of infusion:

Just another post infusion question - my pot of leftover resin got hot and cured but the resin in the tubes is still liquid, is this normal? The inside of the tube got warm earlier. Is it safe to switch the heating off overnight, my conservatory can get quite cold overnight?