On Thu, 07 Jun 2018 22:13:46 -0700, mike wrote:
On 6/7/2018 4:32 PM, Jeff Liebermann wrote:
(...)
In that case, I don't think there's anything you can do to fix it.
Once the water has invaded the pixel area, it's all over.
Yep. The secret to engineering is knowing when to give up.
I was using an Edwards E2M-1.0 2 stage rotary vacuum pump:
https://shop.edwardsvacuum.com/products/r1/list.aspx
It's been run well past its 30,000(?) hr major overhaul point and is
probably leaking around all the rubber vanes and seals. As I recall,
it went down to about 200 milliTorr and refused to go lower, probably
because of leaks in the reinforced fish aquarium I was using for a
test chamber. Water has a vapor pressure of 25 Torr (0.5 PSI), so
that should have easily sucked all the gas and water vapor out even
with all the leaks. I had hoped to see some boiling near the hole,
but didn't see any.
I was experimenting with making heat pipes years ago. I don't remember
the numbers, but 0.5 PSI sounds WAY higher than I was trying.
Vapor pressure of water in Torr:
http://www.wiredchemist.com/chemistry/data/vapor-pressure
and in PSI:
http://www.pumpworld.com/vapor-pressure-chart.htm
25 Torr or 0.5 PSI look right.
As a test, I put the vacuum gauge right on the suction port of the pump.
It went down to where water was supposed to vaporize and stuck there
until I gave up. Reading about it suggested that you have to suck all
the water (and other contaminants) out of the pump oil before you can do
anything useful. They recommended FRESH oil for every evacuation.
I bought some pump oil, but never got around to trying it.
That could have been my problem. At the time, all I had was the oil
that was in the vacuum pump when I bought it used. It probably was
rather dirty and likely contaminated with some water from
condensation. Looking at the pump through the oil level sight glass,
it looks dirty. New oil is about $30/gallon. I was eventually going
to buy the o-ring and basic rebuild kit, at which time I would buy
some new oil. However, I was getting a usable vacuum, so I didn't
bother.
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558