Re: Caring and feeding an Edwards speedivac?
- From: Mark Rand <randm@xxxxxxxxxxxxxxxxx>
- Date: Wed, 26 Sep 2007 23:55:12 +0100
On Wed, 26 Sep 2007 21:56:49 +0200, Nick Mueller <muellernick@xxxxxx> wrote:
Hi!
A Edwards vacuum pump "speedivac" got a new home. :-)) Thank you Bob!
Right after checking wether it runs, I checked the oil level and rushed to a
precision-plus (www.precisionplus.com) dealer near Munich to get a new fill
of vacuum pump oil. The old one was only three spoonfull of brown ump. :-)
As I have no manual (and can't find one on Edwards' site), I have to do some
guesswork.
Air-load: There is a screw (a valve) on top of the pump, that, when fully
closed, makes the pump sound more like a Diesel. Opening, the sound is
getting smooth and air (just a bit) is coming out of the outlet. Fully
opened, the pump makes a boiling sound. I guess this is the air-load. Do I
have to open it when the chamber I'm evacuating does contain some media
that is boiling? Thus it doesn't condense in the pump?
Yes. The ballast allows a small amount of air to leak into the pump to prevent
vapours condensing-evaporating-condensing-evaporating in the pump.
Min pressure: The sticker says 1mm Hg with full air-load. This would
translate to 1.3 mbar. I don't get that according to my pressure gauge. I
do get 30 mbar (gauge is class 1.6) according to the gauge. Now I connected
a container with some water in it and it does boil (a bit) and the reading
then is 50 mbar. Water should boil at 20°C and 20 mbar (at about). So it
looks like the gauge is off by 10 mbar or so.
But I do not get a better vacuum when the air-load is closed (no container,
just the gauge connected to the suction side) Leaks? Still some water
(there was) inside the pump? The plate on the pump says "0.02mm Hg" without
load.
Now should I let run the pump with the inlet closed and the air-load opened
to get rid of moisture inside? When I unscrew the filler cap for the oil
while running, fumes are getting out. Hard to say wether water or oil. I
don't want to open the pump (if it can be avoided) and risk to ruin gaskets
that will be hard to get.
Re-your later comments about the 0.04mm clearance. Don't forget that the vanes
will get quite hot in use. don't make them too good a fit in case they seize.
Have you run the pump with the new oil? Let it run for a while with a closed
inlet and the ballast valve open. Let it get hot to evaporate any moisture and
see what vacuum you get then?
Oil trap:
Ooops! One time, it looked like the pump spilled some oil (I checked the
level, it's OK) out of the suction-side. Do I need a trap or new
gaskets? :-)
Varnish-trap:
Does it make sense (I think) to have a trap that could catch some varnish.
Just in case.
May be simpler than cleaning varnish out of the pump :-)
Besides the questions, the varnish I have now is boiling. That doesn't make
too much sense. I'll phone the dealer and maybe need something different.
Anyhow, I do have an useless prototype in the oven to see what happens.
You said before that the varnish was water based. Is it worth refrigerating it
to lower its vapour pressure? The varnish that we used at work many years ago
was designed for a low vapour pressure, but I don't know what was in it!
Any thoughts and dos-and-donts welcome!
Worth what you paid for them :-)
regards
Mark Rand
RTFM
.
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