Just bought Dahlar RBG 460 and will try it. The first one was tubular too, but for general usage, and wasnt friendly ws resin.

Interesting thread.

The problem was in wrong vacuum film. After infusion resin ate out some micro holes in minutes. I both one from composites seller but with no any data sheet. After contacting they explained that is vacuum film for general usage . Now I changed it and test is good. 2m fiberglass tube with polyester resin infusion one inlet at one end bottom of tube and one outlet on other end top with spiral across the tube took 30min.

Mate, seriously, you are pushing it with a 4m infusion, even2m is pretty optimistic and probably the reason it’s not coming out as youexpected it.

Do a test sheet, layup the same stack sequence on a flatsurface, about 200mm wide and say 2m long. Infuse as you would normally butmark off the resin front every 10/20/30s or whatever depending on the infusionspeed and you will soon see where it starts slowing down significantly. If you use a glass sheet you can seethe resin front at the surface and how much lag you have.

With a 2m infusion I would be looking to place the resinfeed inlet close to the centre of the mould but with a small diameter boom thisis going to be difficult.  Either that ora spiral down 2/3rds of the way or a multiple feed built into the mould.

If you try to do a 4m infusion with a single inlet and you reckon it will take and hour then it's likely that the resin front will stall at some point and you won't get a full infusion

Right, bladder would be the best. My though is to make it from silicone, but not for this tube as it is pretty simple. 

Your application is shouting to me OOA pregreg and bladder pressure tube rather than infusion.

How long is the tube you are making? one inlet close to the end may not be enough to ensure full saturation/infusion as you will get a pressure head drop over the length of the part.

15mins may not be enough to get the air out of the system and again depending on the layup you may inherently get dry spots if air is trapped. Try 40mins+ on vac before infusing and do a vac drop test

Have you got a dam at the end is the outlet driectly fed off the infusion mesh? You could try a slower mesh or a longer dam at the end.

Sorry no ropes but grooves 

To prevent leaking I am using special vacuum sealing type like this. I use it to bond vacuum film to vacuum film or film to mold. Also I am using a specific rubber sealing type between both sides of mold on a flange. Actually now I am making rope 1,5cm wide on a flange of new molds and fill it with liquid silicon so I have reusable sealing type in a right place. 

Yes, spiral can damage vacuum film.

I have to ask what you did to seal the mould split/flange so that air can not get in?