Chromatography Forum

Hi Everyone,
I vented an Agilent 5975C today to clean the ion source as part of some routine maintenance. When I tried to turn the MS back on and pump down, the fore line pump initially turns on, but then shuts down after about 5 minutes. This keeps happening again and again. Any thoughts?

Thanks,
Chemboy

There have been numerous reports in this forum about Pfeiffer forepumps for the 5975C failing as well as leaking oil.

I suspect the pump is faulty and due to an overhaul.

There is a big leak somewhere in the system. If the rough pump has trouble generating certain vacuum level, it will shut down automatilly. Remember to gently push the MS chamber door when you turn on the rough pump.

Like others said, it's either a large leak somewhere or the pump is faulty. How many hours of work does it have?

I spoke with Agilent Support over the phone today and they seem to think the foreline pressure sensor may have died. I'm drawing a vacuum ( if I vent the MS and open the vent valve the system hisses like normal as air rushes into the Quad chamber), so I don't think I have a leak, but I haven't heard of foreline sensors needing to be replaced. Anyone have any experience with this?
Thanks,

Chemboy

Chemboy,

You misunderstood my point. You didn’t have a leak before the maintenance, but there is a leak when you try to pump down the MS. That’s why it shuts down. The possible cause is the chamber door is not completely shut. So try to gently push the chamber door while you turn on the mass spec.

The system was working perfectly, now it’s not after a routine maintenance. It’s hard to believe something failed during the maintenance. Look for the obvious.

Pumpdown failure shutdown
The system will shut down both the high vacuum and the foreline pump if
the system fails to pump down correctly. The conditions that trigger shutdown
are:
• Diffusion pump MSD: foreline pressure above 300 mTorr after 7 minutes
• Turbo pump MSDs: turbo pump speed below 80% after 7 minutes
This is usually because of a large air leak: either the sideplate has not sealed
correctly or the vent valve is still open. This feature helps prevent the
foreline pump from sucking air through the system, which can damage the
analyzer and pump.
To restart the MSD, find and correct the air leak, then switch the power off
and on. Be sure to press on the sideplate when turning on the MSD power
to ensure a good seal.

other test: You can try to connect your pump alone or connect a new pump to your MS...maybe thermal deconnection