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S_Carbon_fibre
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Group: Forum Members
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Hello,
I recently bought the starter kit for VI. I follow the instructions in the video and I am getting a vacuum pressure of around -27.5 but when I clamp off the bag between the vacuum bag and the vacuum chamber, the vacuum gauge goes immediately up. Why is this happening? In the video it stays where it is. Is there a leak in the vacuum chamber? do you have any tips how to check this? many thanks
SH
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Hanaldo
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Group: Forum Members
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There will be a leak somewhere, yes. It is far more likely to be in a hose connection than it is to be in the actual structure of the catch pot itself, so make sure all your hoses and fittings are very tight. Also sounds strange, but check your catch pot lid is securely seated and there is nothing like a piece of stray fibre caught between the lid seal and the lid itself. If the gauge is moving immediately, then it is a big leak. See if you can turn all noise off and listen very carefully for any hissing. With a leak this big, it should be possible to hear the general area it is coming from and then start playing around with things until the noise disappears.
The other possibility is that your hose clamp isn't totally clamping off the hose. These hose clamps have a tendency to bind up and just pinch one side of the hose, leaving the other side with a slight opening, so your leak could in actual fact still be coming from your bag. Might be worth double clamping the hose to check this.
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Matt (Staff)
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+xHello, I recently bought the starter kit for VI. I follow the instructions in the video and I am getting a vacuum pressure of around -27.5 but when I clamp off the bag between the vacuum bag and the vacuum chamber, the vacuum gauge goes immediately up. Why is this happening? In the video it stays where it is. Is there a leak in the vacuum chamber? do you have any tips how to check this? many thanks SH Hi SH, Hanaldo has posted some good points but just reading through your original post again I'm wondering if the problem is actually something slightly different. The title to your post is 'vacuum gauge goes down after clamping off the bag' which I think Hanaldo understood to mean that you lose vac pressure when you clamp the bag off which would suggest that the leak is with your catchpot or fittings but re-reading your post I think that when you say the gauge 'goes down' you mean the vacuum pressure increases; which of course would indicate that the leak is with your bag and not with the vacuum equipment. If this is the case then your question is a very common one and certainly something that's been discussed several times on this forum. What you're looking at is a good old 'leaking bag'. There are many causes and many solutions and which ones to target rather depends on your level of experience with vacuum bagging. If you're relatively new to this then the first thing to know is that getting a vacuum bag to seal properly is not as easy as you might think, especially for a beginner and that leaks (at first) are common. Start by: 1. Check check check, press press press your seal all the way round. Take several minutes doing this, check every last mm of the seal, looking for any stray fibres that might bridge across, wrinkles in the tape, wrinkles in the bag. Press again, squidge it again. Make 100% sure that the seal is good. 95% of leaking bags come from the seal. 2. Check the seal around the fittings; you're doing infusion so you'll have two of the silicone connectors to check. This is much like checking the rest of the seal; look for any wrinkles or creases and press the seal really firmly. 3. Once you've done (1) and (2) if you still have a leak then you might have a puncture in the bag itself. If this is the case then see if you can find it by listening carefully. This rarely works because the leak can be very hard to detect but it's worth a try. If you can't find it then it's probably time to cut your losses and re-bag the part (throw the bag and seal away and start again). The lesson to learn in this case is how the bag might have got punctured in the first place. Before bagging again, check your mould (particularly the reverse side and edges for anything sharp, especially stray fibres of glass etc.). You should cover the reverse of your mould with breather and cover the table you're working on with breather or a rubber mat or similar. Most bag-punctures come from the mould banging against the bagging table and putting a very hard-to-find pinprick or nick in the bag. I hope this helps. What you're going through is very common; bagging will take a long time to get right at first (unless you're lucky) and will still throw you some spanners even once you know what you're doing but it will get easier and quicker. All the best, Matt
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S_Carbon_fibre
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Group: Forum Members
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Hello both,
many thanks for the very quick responses. I think what Hanaldo wrote describes better the problem, once I clamp off the bag between the bag and the catch pot the pressure gauge goes up and stabilizes at about -11.I will check again all the fittings and the catch pot. But it seems the bag is also leaking, after sometime it gets loose and loses the vacuum so this is also very helpful:
"if you still have a leak then you might have a puncture in the bag itself. If this is the case then see if you can find it by listening carefully. This rarely works because the leak can be very hard to detect but it's worth a try. If you can't find it then it's probably time to cut your losses and re-bag the part (throw the bag and seal away and start again). The lesson to learn in this case is how the bag might have got punctured in the first place. Before bagging again, check your mould (particularly the reverse side and edges for anything sharp, especially stray fibres of glass etc.). You should cover the reverse of your mould with breather and cover the table you're working on with breather or a rubber mat or similar. Most bag-punctures come from the mould banging against the bagging table and putting a very hard-to-find pinprick or nick in the bag."
As far as I understand you have to be very careful and patient to get this right...
Best wishes,
SH
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Matt (Staff)
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Group: Forum Members
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+xHello both, many thanks for the very quick responses. I think what Hanaldo wrote describes better the problem, once I clamp off the bag between the bag and the catch pot the pressure gauge goes up and stabilizes at about -11.I will check again all the fittings and the catch pot. But it seems the bag is also leaking, after sometime it gets loose and loses the vacuum so this is also very helpful: "if you still have a leak then you might have a puncture in the bag itself. If this is the case then see if you can find it by listening carefully. This rarely works because the leak can be very hard to detect but it's worth a try. If you can't find it then it's probably time to cut your losses and re-bag the part (throw the bag and seal away and start again). The lesson to learn in this case is how the bag might have got punctured in the first place. Before bagging again, check your mould (particularly the reverse side and edges for anything sharp, especially stray fibres of glass etc.). You should cover the reverse of your mould with breather and cover the table you're working on with breather or a rubber mat or similar. Most bag-punctures come from the mould banging against the bagging table and putting a very hard-to-find pinprick or nick in the bag." As far as I understand you have to be very careful and patient to get this right... Best wishes, SH Hi, yes, you do. We could write a book on vacuum bagging! The best advice I can give anyone experiencing problems is to be logical and isolate individual areas to find exactly where the problem is. If you clamp off very tightly right at the point where the hose goes into the bag (and make absolutely sure that your other hose is properly clamped too) and you lose vac pressure in your bag (i.e. it goes slack after a few minutes) then there is work to do on he bag itself. Secondly; if you clamp off at the bag connection (again making sure this is done very tightly) and you see pressure go down in your catchpot then I'd suggest clamping off the other side of the hose (which goes to the pump) to isolate just down to the catchpot itself and see if the problem persists, if it does, check all those fittings again (especially the seal and gland). If clamping off the hose to the pump fixes the problem then you need to check the fitting into the pump itself (rare but possible, especially if it's been changed). Let us know how you go. If you need direct support then you can email or call us too. --Matt
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S_Carbon_fibre
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Group: Forum Members
Posts: 17,
Visits: 89
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+x+xHello both, many thanks for the very quick responses. I think what Hanaldo wrote describes better the problem, once I clamp off the bag between the bag and the catch pot the pressure gauge goes up and stabilizes at about -11.I will check again all the fittings and the catch pot. But it seems the bag is also leaking, after sometime it gets loose and loses the vacuum so this is also very helpful: "if you still have a leak then you might have a puncture in the bag itself. If this is the case then see if you can find it by listening carefully. This rarely works because the leak can be very hard to detect but it's worth a try. If you can't find it then it's probably time to cut your losses and re-bag the part (throw the bag and seal away and start again). The lesson to learn in this case is how the bag might have got punctured in the first place. Before bagging again, check your mould (particularly the reverse side and edges for anything sharp, especially stray fibres of glass etc.). You should cover the reverse of your mould with breather and cover the table you're working on with breather or a rubber mat or similar. Most bag-punctures come from the mould banging against the bagging table and putting a very hard-to-find pinprick or nick in the bag." As far as I understand you have to be very careful and patient to get this right... Best wishes, SH Hi, yes, you do. We could write a book on vacuum bagging! The best advice I can give anyone experiencing problems is to be logical and isolate individual areas to find exactly where the problem is. If you clamp off very tightly right at the point where the hose goes into the bag (and make absolutely sure that your other hose is properly clamped too) and you lose vac pressure in your bag (i.e. it goes slack after a few minutes) then there is work to do on he bag itself. Secondly; if you clamp off at the bag connection (again making sure this is done very tightly) and you see pressure go down in your catchpot then I'd suggest clamping off the other side of the hose (which goes to the pump) to isolate just down to the catchpot itself and see if the problem persists, if it does, check all those fittings again (especially the seal and gland). If clamping off the hose to the pump fixes the problem then you need to check the fitting into the pump itself (rare but possible, especially if it's been changed). Let us know how you go. If you need direct support then you can email or call us too. --Matt Hi Matt, many thanks these hints are very helpful. I will retry by following your advice. Best, SH
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S_Carbon_fibre
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Group: Forum Members
Posts: 17,
Visits: 89
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Hello,
I managed to find a leak at the connector of the catch pot, this was causing the gauge to go up after clamping off the bag;it is fixed. Since I had a leak in the bag too I am planning to do the process of sealing again very carefully avoiding wrinkles, fibers between the bag and the sealant tape etc. I was wondering, isn't it easier to use two rows of sealant tape around my mould instead of one for better sealing/results?
many thanks for the tips!
SH
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Hanaldo
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Group: Forum Members
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Boeing actually have a patent on the infusion process using two rows of sealing tape. In theory it does give you better vacuum integrity.
In reality, I think it's just a waste. It's perfectly possible to get a perfect seal with one line of tape, so why use double the material?
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S_Carbon_fibre
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Group: Forum Members
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No doubt it is a waste of material but I was just thinking how to increase the possibility of success since I don't have any experience. Is there a way to check and find out where about your bag leaks? many thanks for the very helpful responses.
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oekmont
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The easiest way to do this is a drop test. Clamp the vacuum and the resin feed hose and come back an hour later. If the bag is just as tight as when you left, your seal should be good enough for an infusion.
I myself use a vacuumeter (vac checker by dd compound). I know how much pressure my vac system reaches when everything is tight, and I work at the tacky sealing till I reach that pressure (wich depends on wether conditions too). The advantages of that method are the saved time for the drop test, and instant feedback when I am working at the sealing close to a leak. Keep in mind that a vacuum gauge like yours is not accurate enough for this method. Using a digital vacuumeter was certainly a game changer for me. It cut down my bagging times almost by 1/2.
I would not recommend using double tape sealing. This just complicates things and therefore makes every individual seal less likely to be perfectly tight. Remember that even with this method at least one of the seals have to be perfectly tight. Two almost tight seals are just as good as one almost tight seal. And the problem is usualy just not enough work on the sealant tape, and a double layer doubles that work by definition. With double the work at just one round of tape you will almost certainly get the better result. So focus on one seal, to make it perfect, and not complicate the process with another seal.
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