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Re:Re: Diffusion Oil

>... when your vacuum gauge sensor starts to die, it will give you higher
>and higher numbers for your lowest reading

I missed the first part of this thread. What kind of sensors are we talking
about here, thermocouple? Pirani? (I use pirani and keep it constantly open
to the manifold...no Morgan I'm not trying to be contradictory, just curious
about this...I went through a couple sensors in my first six months with
this guage, but have had the current one on there five years.) 

> When you say they have worked well (Ted) are you basing that on
>vacuum gauge readings?

Yes, plus curing-in "visuals" -- neon tubes instantly red or taking time to
get there; argon tubes instantly dim or a bit bright at first; snaking or not. 

> How low does your gauge read? 

1 micron; HPS pirani-type gauge. Yes, right, the Hastings 1/100th
-micron-type is on the "someday" list; meanwhile this one seems very
consistant. If the needle is buried on "0" it will stay there some 20-60
seconds when I shut the pump valve; if it's at all above zero, even just a
hair,  I can tell there's something degassing a bit still. 

>Have you done oil annalysis on old (changed) oil? 

No.

>How often do you change oil? 

6 months to a year. 

>Do you leave your pumps on/diff pump heater on all the time? 

Yes when in production, ie; on 24-hours/day for weeks or even months; off
when gone or no jobs happening for at least a few days. 

>screwing up the oil by exposing it to atmosphre

My understanding was that old oils are this way; silicone oils are not. I
first used Duniway's "Octoil" (non-silicone) but it wouldn't pump so good
after a few months. Is the Harris book talking about modern oils?

>I had believed that metal pumps were different in tha they ran hotter than
glass
>pumps

Why? metal conducts heat much better; water-cooling is much more efficient
than air cooling. The entire top of my metal pump is COLD to the touch (and
not just on the water coils); the middle, warm, the lower third (where's
there's no coils) very hot (I also wrap the bottom in fiberglass to conserve
heat).

> Any other tips would be greatly appreciated.

A $400 HPS contraption that sits on top of the forepump and ENSURES that
when the anti-suckback valve in your good ol' Welch 1402 fails that the oil
doesn't swim merrily upstream to the diff pump (what a mess :^(...ever try
to clean oil out of one of those coiled-stainless flexible connector
pipes?). It engages in about a half-second in the event of power failure (a
regular occurance here in third-world) and closes it's high-vac valve to the
diff pump while venting to atmosphere the forepump (making it easier to
start). It won't reopen until the forepump has both turned on AND come back
down to vacuum. Handy thing for 24-hours-on pumps. 

-Ted 

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ps Tom your previous posts came through fine here.