Re: Caring and feeding an Edwards speedivac?
- From: "Norman Billingham" <n.billingham@xxxxxxxxxxxx>
- Date: Thu, 27 Sep 2007 11:22:40 +0100
"Nick Mueller" <muellernick@xxxxxx> wrote in message
news:5lvrroFaoiqsU1@xxxxxxxxxxxxxxxxxxxxx
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.
<SNIP>
I may be teaching granny to suck eggs, but I used speedicvac and genevac
pumps for many years in lab work, so here goes.
Normal atmospheric pressure is 760 mm Hg (15 psi). If you pull a vacuum of
say 1mm then the external pressure on the walls is 759 mm. If you go to
0.001 mm the external presusure is 1mm greater! In other words if what you
are trying to do id generate a force, for example for impregnation, vacuum
forming, pressing veneers or making composites then any vacuum is good
enough. The difference between lousy (1 mm) and good (0.001 mm) vacuum is
only important for things like vacuum distillation, or when you need very
pure, clean conditions. Putting it another way, the implosion hazard for a
vacuum of 10 mm is just the same as for a vacuum of 0.001 mm.
Incidentally, there must be loads of these old pumps being scrapped in
university chemistry and physics labs and even pretty much worn out ones are
good enough for many things. I do vacuum bag veneering of wood with an old
genevac which was being scrapped at work. We must have scrapped several
hundred over the last ten years.
A speedivac in good condition, working hard against a closed system and with
well degassed oil will pull about 0.001 mm. For what I think you are doing
(vacuum impregnation?) even a clapped out one will do the job. The vacuum
you can achieve will be limited by the vapour pressure of the liquid which
will be quite high if it's solvent based.
The gas ballast valve leaks a small flow of air into the pump on the exhaust
side. Its job is to help flush crap out of the oil, but it also slightly
reduces the ultimate vacuum. In my spedivac days, we ran with it closed
most of the time and opened it for a while every now ang agin to clean the
oil.
Some more egg sucking points:
Don't run the pump for long periods with the inlet open - you'll aerate the
oil and spray it out of the exhaust.
Don't turn the pump off without letting air into the inlet (some have auto
air admission valves) - you'll suck oil out of the pump into the equipment.
Do have a pipe on theexhaust leading outside - all the crap which goes into
the pump comes out the exhaust.
Don't expect full vacuum immediately from a newly filled pump - it can take
an hour of two to degas the oil.
Hope granny is of some help!
.
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