Weird vacuum issue

General Composites Discussions Composites Talk
#1

I never had this before, hope someone can help.

Its worth noting that I have allways used Tygavac’s pinky/orangey bag. for large parts, I normally spit the bag in 2 and make a large bag. This was very time consuming, so I decided to source some large bagging.
This bagging was more pink and quite “crackly” when being pulled down. Anyways, I pulled vacuum as normal, debulked, and hooked up my gauge onto a connector on the other side of the bag/part. It read -0.9, so I thought I had a leak. went around the tape, didnt see anythign but pressed it anyway. Still -0.9. Thought my gauge was broke, so I hooked it straight to my vacuum, -1.0. Nothing unusual, I must have a leak somewhere, but just in case, I did a drop test. I connected the gauge, pulled vacuum, it went down to -0.9, and unhooked the pump. I went for lunch and came back. Still at -0.9. Left it for 3 hours. still -0.9.

Whats going on here? LOL

#2

Hmm. Gauge is connected well to the part? you don’t have it in a weird place, that gets cut off somehow?

Also, I think I’ve noticed vacuum differences between having the gauge connected to the part, vs. the pump itself. Maybe it’s a weird volume thing.

#3

No, there’s a piece of breather covering the whole part and the 2 connectors are on both ends of the breather. Tried swapping them around as well.

#4

If the bag seems more “crackly” than normal, its most likely a humidity issue with the bagging film. Nylon vacuum bags (I’m assuming that is what you are using), when dry, will be less pliable (crackly) and stiff which can lead to pin holes developing over the surface of the bag. I’d check over the full surface of the part and see if you can find any pin hole leaks.

To avoid the crackly effect, its best to keep the film in a fairly humid environment before you use it (check with the manufacturer for a humidty range). Once you have the bag on the part you can spray it down with a water bottle if the humidty is really low and you need to debulk for a while.

#5

Yes, it was an old bag, and I have been informed about spraying the bag. I’ll try it next time I use it. Thanks.