Pumping system operational again ....

John Shott shott at stanford.edu
Thu Apr 8 21:14:26 PDT 2010

MRC Community:

After a true team effort, I believe that the MRC diffusion pump woes are 
behind us.  This all began with Jim Kruger's discovery a few days ago 
that the foreline/roughing valve had been left in the intermediate 
"don't pump on anything" position ... followed shortly by observed poor 
pumping performance.

In the process we found the following problems:

1. The pump oil in the diffusion pump was quite low.  We resolve this 
with the addition of 300 cc (approximately) out of a total charge of 500 
cc of Santovac 5 diffusion pump oil.

2. The heater element was found to be an open circuit.  After taking it 
apart there was evidence that it had shorted to the pump body at some 
point ...

3. The shorting action likely blew the fuse of one of the two power legs 
of the 208 VAC power.  Initially I had a hard time tracking this down 
because the body of the fuse holder, rather being in the main fuse 
panel, is tucked into the body of the power distribution section.

4. After all of this, I was unable to get the main AC power back to the 
diffusion pumps ... but, fortunately, Eric and Jim Kruger managed to get 
the power turned back on ... and it appears as if the DP heater is 
working properly.

Mihir Tendulkar is running the system now and will hopefully report his 
results or any anomalous behavior.

Please check things carefully before running this system on important 

I'd like to thank both Jim Kruger and Eric Perozziello for their help in 
getting this problem resolved.  I'd also like to apologize to those that 
have been inconvenienced by the delay in getting the system operational 
... I fear that I am not as quick at effecting repairs of this type as 
the regulars on the job.

Thank you for your continued support,


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