My vacuum / pressure set-up

Well I finally got my vacuum set-up done for my pressure pot. I am using a venturi vacuum pump (top left of photos) off the compressor, but arranged my gauges and valves so I can do vacuum and pressure (I need this mainly for banksia). I used a heap of in-line ball valves with simple tee's because the three way ball valves cost a lot more (almost 3 times more).

Photo 1 - Vacuum drawn using air. My venturi pump works under 5.5bar (80psi) air pressure and should draw 29". After 1 min I have 22" Hg (75kPa) vacuum, 4 min 25" Hg(85kPa) and still rising but sloooowly (it is a big old cast aluminium pot).

Photo 2 - Vacuum with air turned off (and pot held vacuum without loss).

Photo 3 - Vacuum released and pressure applied to pot at 3bar (40psi). The pot can take 5.5bar (80psi) max, but I worry about my resin saver moulds leaking at that pressure.

Photo 4 - Pressure holding with air disconnected (and again pot held pressure).

My pot is pretty old, at least 40 years. It started as a glue pot in a workshop, then a paint pot for my father, now a casting pot / paint pot for me. It is a cast aluminium pot and approximately 25mm (1") thick minimum. Hopefully fatigue failure is still a long way off.

Can't wait to try it out this weekend, hopefully filling the pot with blanks will reduce the volume and achieve a higher vacuum. The cool weather at the moment will also allow a bit more time for vacuum before I hit the pressure.

Cheers

I've read that you should not go beyond 27 Hg. It does something to the chemicals. You might do some searching here for the thread(s).

Hmm, can't say I've read anything along those lines. When I searched previously I read 29" was recommended at which point the air rapidly expells.

Dai Sensei said:

Hmm, can't say I've read anything along those lines. When I searched previously I read 29" was recommended at which point the air rapidly expells.

Click to expand...

Try this:
http://www.penturners.org/forum/showthread.php?t=51895

see response #5

Thanks for the link.

By turning off the valves I can just vacuum the line only, and could only vacuum to just over 25" (about 90kPa). So no chance of getting any higher.

Did a cast today and it seemed to pull the air from the banksia, but I still had problems with some voids when casting horizontally, as the bubbles were being drawn up throught the timber not down and out. I then went to vertical casting, which seemed to allow the bubbles to be extracted via the sides, but it also pulled the resin through the gaffa tape I use to seal my electrical conduits.

Looks like I need to stick to vertical casting for the banksia, but need to work out a better way of sealing my split conduits.