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Lester Populaire
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+xDont worry about the gauge, they are all going to be inaccurate in one way or another. Some may be better calibrated than others, but at the end of the day the number they point to really doesn't matter. Keep in mind that elevation above sea level and atmospheric conditions will change the reading the gauge gives you as well. So one day it might read 26", the next day it could be 30mm past the 30" mark - and I promise you wont be pulling 32" of vacuum! Stick with what you've got. Your pump should be perfectly capable of pulling full vacuum, so if it goes quiet and stops emitting oil vapour when the gauge says you are at full vacuum then you are likely at full vacuum. If you're really worried about it, do some playing around and infuse some flat sheet. You'll learn a lot, and you'll also be able to look at the flat sheet and diagnose any problems - pump related problems are going to be obvious. I would highly recommend infusing some flat sheets of glass fiber and carbon fiber and whatever to figure out all small details of the process!
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Hanaldo
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Dont worry about the gauge, they are all going to be inaccurate in one way or another. Some may be better calibrated than others, but at the end of the day the number they point to really doesn't matter. Keep in mind that elevation above sea level and atmospheric conditions will change the reading the gauge gives you as well. So one day it might read 26", the next day it could be 30mm past the 30" mark - and I promise you wont be pulling 32" of vacuum!
Stick with what you've got. Your pump should be perfectly capable of pulling full vacuum, so if it goes quiet and stops emitting oil vapour when the gauge says you are at full vacuum then you are likely at full vacuum. If you're really worried about it, do some playing around and infuse some flat sheet. You'll learn a lot, and you'll also be able to look at the flat sheet and diagnose any problems - pump related problems are going to be obvious.
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quinn
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+xLikely to be somebody else using an analogue vacuum gauge to judge the pumps performance. Analogue vacuum gauges are too relative to be accurate, they dont know what your atmospheric conditions are, they dont know what your elevation above sea level is. They're an indicator but that's it. You need an absolute pressure gauge to have an accurate representation of vacuum level. What sort of pump did you buy, can you show us? If it is a rotary vane pump, it should be able to achieve 99.99% vacuum, even if it is a cheap one. As for why infusion needs full vacuum; the mechanical force behind the process is the atmospheric pressure driving the resin through your laminate. 1 bar isn't a lot of pressure to begin with, and this actually drops as the resin enters the laminate and the pressure differential balances back out. So when the infusion is completed, you don't actually have 14.7psi of pressure on the bag anymore. If you're starting lower, then not only does your resin have less force driving it into your laminate (which increases the likelihood of poor wet-out) but you also have a lower consolidation pressure as a result, which in turn means that you have more space between fibres which must fill with resin so you end up with a resin rich and heavier laminate. There's also air inclusion. The two main benefits of resin infusion from a performance perspective are lower resin content from higher consolidation pressure, and very low void content due to the fact that all air has been evacuated from the laminate before any resin is introduced. If you dont have full vacuum, then you have air inside the laminate which will present itself as voids. Not only will this give you a weaker part, but there's a good chance it will present itself as pinholes on the surface of the part. The difference between 14.7psi and 12.7psi may not sound like much, but every micron counts. Ask anyone that has made a mistake and let just a tiny bit of air into the bag during infusion - it shows up. Even a 0.1% drop in vacuum pressure will cause defects, let alone 15%. This may not mean you end up with a completely unusable part, it depends what you consider acceptable. You will have voids, you will have a heavier part. You basically lose all the performance benefits of having done resin infusion over a wet-layup. Thanks for the explanation, makes more sense now. Not just about how much pressure is being put on the laminate, but also the amount of air left inside. At 80% or so vacuum there's like 200 times the amount of air left in there compared to 99.9% vacuum. Yes, it's a rotary vane, single stage 4.5cfm. Here's the link. 4.5CFM Single-Stage Rotary Vane... https://www.amazon.com/dp/B01MY0C5EZ?ref=yo_pop_ma_swf what worries me is that I've watched about 15 different videos on infusion and every single one of them is using an analog gauge that pegs all the way out to 30 when they pull the vacuum. Is it pretty unlikely that my pump would fail in a way that only pulls partial vacuum? Just not feeling super confident after seeing so many videos of the gauge pegged at 30 and mine only hits 26. Maybe I should go get another gauge?
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Hanaldo
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Likely to be somebody else using an analogue vacuum gauge to judge the pumps performance. Analogue vacuum gauges are too relative to be accurate, they dont know what your atmospheric conditions are, they dont know what your elevation above sea level is. They're an indicator but that's it. You need an absolute pressure gauge to have an accurate representation of vacuum level.
What sort of pump did you buy, can you show us? If it is a rotary vane pump, it should be able to achieve 99.99% vacuum, even if it is a cheap one.
As for why infusion needs full vacuum; the mechanical force behind the process is the atmospheric pressure driving the resin through your laminate. 1 bar isn't a lot of pressure to begin with, and this actually drops as the resin enters the laminate and the pressure differential balances back out. So when the infusion is completed, you don't actually have 14.7psi of pressure on the bag anymore. If you're starting lower, then not only does your resin have less force driving it into your laminate (which increases the likelihood of poor wet-out) but you also have a lower consolidation pressure as a result, which in turn means that you have more space between fibres which must fill with resin so you end up with a resin rich and heavier laminate.
There's also air inclusion. The two main benefits of resin infusion from a performance perspective are lower resin content from higher consolidation pressure, and very low void content due to the fact that all air has been evacuated from the laminate before any resin is introduced. If you dont have full vacuum, then you have air inside the laminate which will present itself as voids. Not only will this give you a weaker part, but there's a good chance it will present itself as pinholes on the surface of the part.
The difference between 14.7psi and 12.7psi may not sound like much, but every micron counts. Ask anyone that has made a mistake and let just a tiny bit of air into the bag during infusion - it shows up. Even a 0.1% drop in vacuum pressure will cause defects, let alone 15%. This may not mean you end up with a completely unusable part, it depends what you consider acceptable. You will have voids, you will have a heavier part. You basically lose all the performance benefits of having done resin infusion over a wet-layup.
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quinn
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+xAbsolutely, analogue gauges are extremely inaccurate. That number will change with the weather as well. They are really only useful as a relative indicator of your vacuum dropping, so you can pull full vacuum and ignore the specific number the gauge tells you, but just see if it is moving at all - if the needle moves then you have a leak. They aren't any good for anything more than that. Fairly sure the analogue gauge I have also reads 26", or somewhere thereabouts. If your pump is specified to 150 micron then it's almost certainly achieving it and the gauge is telling you lies. It's very unlikely its a faulty pump, and if it were then I'd be sure you would hear it in the pumps operation - the pump would sound like it is struggling. well it is a somewhat cheap 80 dollar pump. It had good reviews on amazon, but there was one review out of about 50 where a guy stated it only pulled 25 or 26 inches. when i looked up the gauge specs it says within 3% accuracy so shouldnt be off more than an inch but who knows. how would i know if its actually hitting near full vacuum without a very expensive gauge? is there some kind of cheap test that can be done? so lets say it really was only pulling 26 or so inches, proportionally that would mean im getting 12.74psi pushing on the lay up instead of 14.7psi right? would it really make that much difference? why is it so important to get that close to full vacuum?
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Hanaldo
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Absolutely, analogue gauges are extremely inaccurate. That number will change with the weather as well. They are really only useful as a relative indicator of your vacuum dropping, so you can pull full vacuum and ignore the specific number the gauge tells you, but just see if it is moving at all - if the needle moves then you have a leak. They aren't any good for anything more than that. Fairly sure the analogue gauge I have also reads 26", or somewhere thereabouts.
If your pump is specified to 150 micron then it's almost certainly achieving it and the gauge is telling you lies. It's very unlikely its a faulty pump, and if it were then I'd be sure you would hear it in the pumps operation - the pump would sound like it is struggling.
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quinn
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Group: Forum Members
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+xHow are you measuring the vacuum level though, just an analogue gauge? Or do you have a digital gauge? Analog gauge, but with it reading only 26 inches, there's obviously an issue right? Could analog gauge be that far off?
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Hanaldo
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How are you measuring the vacuum level though, just an analogue gauge? Or do you have a digital gauge?
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quinn
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Group: Forum Members
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+xNo, you really need a minimum of 29.95". Ok, yeah definately a faulty pump. Advertised to hit 150micron, obviously not even close at 26 inches. Getting it replaced. Just out of curiosity, why is it so important to get like 99.9% vacuum? There's only 14.7 psi pushing on the lay up at full vacuum, so let's say you only hit 29 inches, that's 14.2 psi instead of 14.7. why is it so important to get that last tiny bit of vacuum?
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Steve Broad
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