Foreline can only be measured on MSDs equipped with a diffusion pump. At typical column flows (0.1 - 2.0 mL/minute), the foreline pressure will be approximately 20 - 100 mTorr. If the foreline pressure is below 20 mTorr, check the following:
Make sure the column flow has not been reduced or turned off. Column flow should be at least 0.1 mL/minute. Make sure the column is not plugged.
CAUTION! Heating a capillary column with insufficient column flow can damage the column.
Columns can be crushed by overtightening the nuts at either the injection port or the GC/MSD interface. Columns can also be plugged by column fragments. Check both ends of the column. If necessary break off the first few centimeters of each end of the column (remember, this will change retention times slightly).
This would probably create a fault condition in the GC that would prevent the GC from operating. Make sure the carrier gas supply is not empty. If the carrier gas supply is empty, or if its pressure is too low, an alarm should sound and a message should appear on the GC keypad.
This would probably create a fault condition in the GC that would prevent the GC from operating. Make sure the carrier gas tubing is not constricted. If the carrier gas tubing is constricted, an alarm may sound and a message may appear on the GC keypad.
Replace the foreline gauge. See the MSD maintenance documentation for instructions for replacing the foreline gauge.