VHS-4, VHS-6 and VHS-250 Diffusion Pumps - Ideal Vacuum ...

DRAFT 3/9/05
4-2
VHS-4, VHS-6 and VHS-250 Diffusion Pumps
4.3 Poor Pump or System Performance
Before proceeding with a step-by-step troubleshooting program, check the performance and
accuracy of the vacuum gauges used on the system. Table 4-1 shows the most frequent
faults, their probable causes, and specific repair actions required for each.
Table 4-1 Troubleshooting
Symptom Probable Cause Repair Action
Poor system pressure Leak in system — virtual or real. Locate and repair.
High process gas load. Measure gas load,
and eliminate the cause.
System dirty. Clean system to reduce
outgassing.
Poor ultimate pressure Contaminated pump fluid. Examine, clean pump,
and replace fluid.
Slow pumpdown (prolonged
cycle after checking gas load
conditions)
Low heat input. Check voltage.
Check for continuity, burned out
element, poor thermal contact.
Inadequate cooling water flow. Check water pressure. Check
tubing for obstructions or
backpressure.
Excessive or too cold
cooling water.
Check temperature, adjust flow.
High forepressure. Check for leak in foreline, poor
mechanical pump performance,
breakdown of mechanical pump
fluid.
Water in Quick Cool Coil. Check and remove water.
Low heat input. Check heaters.
Low oil level. Add oil.
Malfunctioning pump assembly
Improperly located jets.
Damaged jet system.
Check and repair or replace.