Saving LCD screens that were under water

Started by Unknown June 7, 2018
On Sat, 09 Jun 2018 05:08:37 -0700, mike <> wrote:

>On 6/7/2018 10:46 PM, Jeff Liebermann wrote: >> 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: >>>> <> >>>> 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: >> <> >> and in PSI: >> <> >> 25 Torr or 0.5 PSI look right.
>If my google is right, HVAC systems are typically evacuated below >500 microns to get all the water out. That's more like 0.5 Torr.
The point at which water starts to boil at room temp is 20,300 microns of Hg or 0.393 PSIA or about 20 Torr. Presumably, that's when the water starts to turn to vapor which can the be removed by the pump. However, at this pressure, it will take forever, so a much lower vacuum is probably more practical. Whether it needs 40x more, I don't know.
>My memory is vague, but somewhere under 2000 microns was where >the pressure stopped decreasing due to water contamination. >With even the slightest >leak in the system, I couldn't get there.
When I filled my aquarium with water, applied a vacuum, and looked for bubbles, in order to check for leaks, I found quite a few. These were duly plugged with RTV. I had no trouble going down to what I thought was 200 milliTorr (0.00386 PSI), but now I'm not so sure. I have the vacuum pump and gauge and might be able to try again, but not for a while. I would need to build a new vacuum test chamber and don't have the time, bench space, fresh vacuum oil, fittings, rebuild kit, etc.
>>> 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 Santa Cruz CA 95060 Skype: JeffLiebermann AE6KS 831-336-2558