Vacuum manifold pressure can only be measured if your MSD is equipped with the optional gauge controller. At typical column flow rates (0.1 – 2.0 mL/minute), the vacuum manifold pressure will be approximately 1 × 10^-6 to 1.4 × 10^-4 Torr. If the pressure you observe is significantly above 1.4 × 10^-4 Torr, or if the pressure you observe for a given column flow has increased over time, check the following:
On MSDs equipped with a diffusion pump, column (carrier gas) flow should not exceed 2.0 mL/minute. On MSDs equipped with a turbomolecular pump, column (carrier gas) flow should not exceed 4.0 mL/minute. Reduce the column flow and retune the MSD.
If the oil level is low or the oil is contaminated, the foreline pump will not work effectively. This can increase both foreline and vacuum manifold pressure. Check the level of the oil in the foreline pump. If necessary, add foreline pump oil or replace the oil. Also check the condition (color) of the oil. The foreline pump oil gradually becomes less effective as it is subjected to heat, air, water, solvents, and samples. One symptom is a gradual darkening of the oil.
Check the foreline hose. Make sure it has not collapsed. Make sure it is not bent sharply or otherwise constricted.
If its fluid level is low, the diffusion pump will not work effectively. Check the level of the fluid in the diffusion pump. If necessary, replace the diffusion pump fluid.
See the MSD maintenance documentation for instructions for checking and replacing diffusion pump fluid.
Poor diffusion pump performance is usually caused by a low diffusion pump fluid level or contaminated diffusion pump fluid. It can also be caused by misaligned components in the diffusion pump stack. Misaligned stack components should be very rare since in normal operation and maintenance the stack is never removed. If the diffusion pump fluid level and condition are correct and the stack has not been removed recently, contact your Agilent Technologies service representative.
View MSD temperatures and vacuum. Unless the MSD is in the process of pumping down, the turbo pump speed should be 100%. If the speed is significantly below 100%, your turbo pump may not be working correctly.
Listen carefully for a high-pitched whine. A turbo pump that is operating correctly should be silent. If you hear a whine that is not part of the normal ambient sound from your MSD (fans, etc.), your turbo pump may not be working correctly.
If your turbomolecular pump is not running at 100% speed or is making an unusual noise, contact your Agilent Technologies service representative. The turbomolecular pump is not customer replaceable.