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Tips on Roughing Pressure

Posted: Wed Jul 11, 2018 2:25 pm
by Jeremy Adams
It turns out my dual stage 12 CFM roughing pump is only reaching 40 microns at its lowest. I would prefer it to reach at least 15 microns for roughing my diffusion pump. It is only about one year old and doesn't have much wear so it should be capable of achieving close to its rated ultimate pressure of 2 microns. The connection to the pressure gauge when it reached 40 microns was KF sealed and seemed leak proof but I can double check this. I also replaced the oil and cleaned out old dirty oil in the box holding the motor.

Is the oil I'm using good enough for the roughing pump? It is Mobil 1 vacuum oil, picture attached below. What else can I do to get lower roughing pressure?

Re: Tips on Roughing Pressure

Posted: Wed Jul 11, 2018 3:05 pm
by John Futter
What does the manual for your pug say as to the reccommended oil?
Is this a direct drive or pulley driven pump? A pic of pump would be nice
Have you rung Mobil's tech department to check whether the mobil oil is actually a replacement for the reccommended oil?
Have you run the pump with gas ballast open for a couple of hours to rid the oil of volitles?

Re: Tips on Roughing Pressure

Posted: Wed Jul 11, 2018 5:51 pm
by Jeremy Adams
The manual is vague and says that a 'High Vacuum Pump Oil' is required but does not specify a brand or type. I can try to get in contact with someone who knows about this oil but it's unlikely they will confirm it works for my pump specifically (which is why I posted here to see if you guys know more about roughing pump oil). Attached is a picture of the type of roughing pump I'm using. Pretty sure it is a direct drive pump.