On Aug 18, 9:56 pm, Yukio YANO wrote:

I've run Ultra High Vacuum systems for 40 years with no serious problems
!, Electron Microscopes !

My son was supervising the operation of a Mass-Spectrometer with a
Turbo-Molecular pump, RVP system when a Carbon-Fiber Vacuum coupling
failed on the high Vacuum side.
I don't know what it cost the manufacturers for repairs , but I know
the TMV pump tried to go into Full-afterburner mode and filled the
Ultra-high Vacuum system with pulverized metal dust when the TMV-pump
swallowed atmospheric air ! Which is why the inclusion of the
"electronic safety valve" This probably saved your TMVP!

I would suspect the diaphram in the "electronic safety valve" ruptured
on the roughing pump side and protected the TMVP and shut it down safely

It is ironic but a 2 stage rotary vacuum pump is not really designed to
handle large volumes of air. 99% of its operating cycle is pumping at ~
10u pressure. The exhaust port is part of a reed valve set-up sealed by
the flat spring-like reed which is made gas-tight by the oilbath
reservoir. Normal operation has only a trickle of bubbles flowing out
from under the spring, usually from bypass operation to flush moisture
(condense-able vapors ) from the pump. It is only during the initial
roughing cycle that a significant amount of air flows though the pump
and carries a small amount of atomized Vacuum pump oil with it, hence
the oil mist filter. The RVP is designed to pump down a Closed system.
not an open to the atmosphere system, so it is no surprise that it
flushed out its charge of oil when it was opened to the atmosphere.

BTW Philips/Ewards High Vac. now recommend using "AMSOIL" Compressor
oil ISO-46 (PCI) SAE 20 for their Vacuum Pumps. Much better pump life !

Yukio YANO



As a matter of fact, most of the UHV parts I used to build this
(including the turbo) were from an electron microscope that we got
donated in surplus.
The diaphragm didn't rupture. The solenoid that opens the valve
melted. And yes, as you pointed out, failures in these valves are
designed to close off the UHV from the roughing side to keep from
destroying our expensive stuff.

Thanks for the info on roughing pumps though. Interesting stuff...

-Matthew