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Thread: Vacuum versus pressure
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19th February 2021, 02:25 PM #16GOLD MEMBER
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Thanks Neil.
What size and brand/manufacturer is your pressure pot.
In the aviation industry we concern ourselves re pressure cycles. Actually count them, to enable structural analysis and determine specific maintenance and inspections.
Is your pressure pot up to Aust stds? What'd be your highest pressure and for how long? 40-60psi for 24 hours???
Thanks for answering these questions, it is much appreciated.
Lyle
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19th February 2021 02:25 PM # ADSGoogle Adsense Advertisement
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19th February 2021, 05:16 PM #17
I have a number of pots, an old 10 litre cast aluminium (that I do worry about fatigue, so rarely use these days), an old 20 litre steel pot made by a boiler maker (and definitely over designed), and a good quality 30 litre bought off Ebay. I run them within a closed shed for added safety. Generally they run for 24 hrs at a time at less than their design working capacity with safety valves I installed set for their safe working load. The aluminium runs at 50psi/60psi (because it's so old), the steel at 60psi/75psi and the new one 75psi/80psi (working pressure/safety valve).
The cheap Chinese ones from Ebay/Super Cheap etc are ok but do have a limited life. Cheap ones have no seats for the hold down bolts and mark the lid steel. This is where they fail due to fatigue, so many put copper/brass/protector discs under the bolts so as to avoid stress concentrator points in the lid.Neil____________________________________________Every day presents an opportunity to learn something new
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28th March 2021, 07:45 PM #18
There's an Australian company that sells pressure pots for paint but does some modifications to make them suitable for resin casting including trimming the agitator. Don't know if they're ok with me posting name here so PM me.
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29th March 2021, 01:21 PM #19
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29th March 2021, 04:03 PM #20.
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I've been watching a few vids on this top and a technical explanation for bubbles disappearing under pressure seems to be missing.
I don't think the added pressure actually shrinks bubbles to invisibility because the pressure changes alone not large enough to do this.
A 3 mm radius bubble under say 3x original pressure will only shrink the bubble to about 2mm in radius which would be easily visible.
For it to become invisible the air must be dissolving into the resin.
This is why soda water under pressure is transparent - the CO2 has been dissolved into the water. When the external pressure is release the CO2 no longer can stay in solution and so starts appearing as bubbles.
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29th March 2021, 09:13 PM #21SENIOR MEMBER
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Lyle can you give an example of what sort of voids you are wanting to fill?
Maybe if they are open ones you can sand, shallow or you use coloured resin, you maybe not even need a pressure pot.
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30th March 2021, 09:14 PM #22Neil____________________________________________Every day presents an opportunity to learn something new
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3rd April 2021, 02:33 PM #23
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4th April 2021, 02:09 PM #24
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