Leak Detection

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#1

How do you guys find leaks in your bags? Short of an ultrasonic leak detector. I’m open to suggestion on which ultrasonic leak detector is best, but right now I need to find one I have.

It’s dropping an inch in two or three minutes, so it’s a pretty big one. Still I can’t hear it.

I have tried the usual stuff like looking for places that might not be sealed well, and rubbing the tape all over the bag to help it seal.

I have done the spray adhesive thing before, but usually when I know where the leak is. I thought of brushing a little food coloring around everything and see If it will suck in and make a stain somewhere.

Any ideas?

#2

99.9% of all leaks are at the sealant tape, unless you have cheap bag film or you’re man handling it. Just visually check the tape up close you can find all leaks. If there is a small hole in your bag usually ultrasonics are useless anyway.

#3

99.9% of all leaks are at the sealant tape, unless you have cheap bag film or you’re man handling it. Just visually check the tape up close you can find all leaks. If there is a small hole in your bag usually ultrasonics are useless anyway. it’s good to isolate your vac pot and leak check them often

#4

It’s stretchlon 800. I have looked at the tape seams. The I disconnected the pot to help isolate the leak. I also used vacuum grease on all of the fittings.

#5

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ten signs

#6

You are basicly right, although SL800 usually is OK.

#7

May be, but for infusion I would always use a multilayer bagging film (PA/PE or PA/PP). The stretchable bags are great for vacuum pressing of wet layups or if you have a double bag system.

#8

If you are talking about an envelope style bag you don’t need to use tape at all. I seal mine using a food bag melt sealer. I use Stretchlon and it works great. I always melt a double seam just to make sure but once is normally enough.

The only leaks I ever get are when I forget to cover sharp points. They can be a PITA to find. Look for anything that isn’t totally flat, even if it doesn’t look like it’s making a hole.

@Herman: how is the testing of those different models of US detectors going?

#9

Cheapest leak detector is a stethoscope with the head removed and a piece of metal tube. If you can’t find the leak. Bag over everything a second time.

#10

I know this goes against the norm…but I when I can’t find a leak, I shoot the part, usually I find it then…I follow the air bubbles and start taping or spray adhesive the area. 9 times out of 10, leak is stopped…just run a slow infusion when you start so the resin isn’t 10 miles from the leak area and you’re screwed. If you can catch the leak when the resin hits the area that has the hole in it and catch in time, the air will usually get sucked out and all is fine.

^^Please take with a grain of salt, it can happen that the part gets air and maybe a waste if you follow this advice, but when you can’t find the leak and don’t feel like re-bagging the part or double bagging, this is usually the only option left.

#11

Still not tested. I really should be testing it.

As for shooting with a leak. sometimes you have to. You cannot just wait for the leak to disappear. As the project gets larger, leaks cannot be completely avoided. A friend of mine did a 62 meter boat. They had leaks somewhere, I am sure.

#12

At such large projects I always reccomend to double bag for vacuum integrety. You will have a leak somewhere in a single gan at this size, and you will not find it

#13

I’ve done this with non critical parts, just shoot the resin through and find the leak when it shows up. Sometimes it never does and the bag fills with air throughout the cure but the part turns out to be acceptable. This is luck though and I wouldn’t take this approach if you have customers.

#14

So Im guessing there is no good solution for finding small leaks, I read here many stories of 1000$ bucks leak detectors which simply dont do the job… its sad

#15

It’s really an art learning to use a leak detector. One of the best improvements I made with mine was I bought a good pair of ear plugs for mine. They cancel out the outside noise and help find a leak. Sometimes it just takes persistance to find a leak. You’ll hear a signal from an area that’s maybe a foot away from the actual leak. Usually where there are several folds in the bag. Make sure your mold has no sharp edges or points. I rub my hand slowly across the mold back looking for sharp points.

#16

Helium leak detectors but they are pricey

#17

I use the accutrack and like it. Comes with headset.
$350

http://www.tequipment.net/AccuTrakVPE.html

#18

I was under the same impression, I can not believe that an US leak detector is worth 1000$ or more. So I investigated an alternative: ultrasonic Bat detectors. The are doing more or less the same thing and are much cheaper to source. Starting at 30 bucks the top models cost 1000$ too, but then you have a product, which is worth the money.
The main difference is, that you can/have to tune most of the bat detectors, so you can tune them to the frequency of larger or smaller leaks, but you can also miss the one or the other when tuned wrong.
I have to admit that I haven’t bought one yet, but will in the next few months and then I can tell you my first hand experiences.

#19

So this is the major disadvantage of infusion proccess, If you cant find leak you will fail , especially with bigger projects like hoods, and few x 100$ lands in rubbish

#20

No, you can infuse evenwith leaks. But you will have to stay alert during the infusion, to correct the problem during the infusion. Several options for finding leaks.

Assuming the mould is airtight (I hope that has been tested, leaky moulds during infusion are never nice) you have only a couple of possible leak paths. I also assume the use of proper materials, not cutting corners using cheap materials from unknown sources.