Chromatography Forum

My lab inherited an Agilent 5977b MSD (Firmware ver. 6.00.35) with our Agilent GC. The direct-drive rough pump is powered through the MSD.

The system has some peculiar vacuum pump behavior.

When shutting down/venting the MS from the MassHunter software, the turbo pump slows, but the rough pump never shuts down until we power off the MSD.

Shouldn't the rough pump shut down automatically once the turbopump is below a certain speed and vent valve is opened?


On power-up, the rough pump and turbopump both start immediately as soon as the power switch is engaged. This is before the MSD has booted or even connected to the MassHunter computer. The MassHunter computer then shows Turbopump struggling at 3% and the pump down process is already underway when the MSD finally connects to MassHunter (without issuing the pump down command). In a minute or two enough vacuum develops holding the door closed that the turbopump accelerates.

Is this normal vacuum pump sequencing behavior for the 5977b? Doesn't the turbopump normally wait for a command or minimum vacuum or rough pump run time before starting?

Don't worry. It behaves as it should.

Many thanks! So many models of GC-MS and LC-MS/MS and in my lab and each one pumps down and vents slightly different even from the same manufacturer. The manuals usually cover multiple models, each with slight differences in procedures. So it appears that it impossible to actually issue a pump down command with this instrument during power-up, since the MSD is already pumping down when the computer finally connects.

The rough pump should bring the vacuum down within 15 seconds or so after it starts, if it is taking longer be sure you press in on the center of the side door when turning on the power and do not tighten the screw holding the door closed more than slightly finger tight. Over tightening can deform the o-ring and not let it seal easily.

You normally hear the rough pump switch from a louder gurgle sound to a normal hum as the vacuum is established that is when the turbo pump can really begin to pick up speed.

...So it appears that it impossible to actually issue a pump down command with this instrument during power-up, since the MSD is already pumping down when the computer finally connects.

In fact you don't need a computer to pump down 5977 MSD.
It starts pumping down immediately after switching on instrument. However it heats the source and quad to 100 deg C, not to last working temperature.