Maintenance - Welch CHEMSTAR 1374N Owner's Manual

Section 3: MAINTENANCE
3.1 Vacuum Problems
3.1a Pressure Determinations
Leakage, contamination and unusual outgassing are the general causes of problems associated with poor vacuum.
To operate at maximum efficiency a system must be thoroughly clean. If the system is completely clean and free
from leaks, and unwarranted vacuum problems still exist, the pump should be checked. A simple criterion for the
condition of a mechanical pump is a determination of its ultimate pressure capability. This can be accomplished
by attaching a gauge directly to the pump. The gauge may be any suitable type provided consideration is given to
the limitations of the gauge being used. Refer to Paragraph 1.8 for further suggestions. If the pressure is
unusually high, the pump may be badly contaminated, low on oil or malfunctioning. On the other hand, if the
pressure is only slightly higher than the guaranteed pressure of the pump, an oil change may be all that is required.
3.1b Oil Contamination
The most common cause of a loss in efficiency in a mechanical pump is contamination of oil. It is caused by
condensation of vapors and by foreign particles. The undesirable condensate emulsifies with the oil which is
recirculated and subjected to re-evaporation during the normal cycle of pump activity thus reducing the ultimate
vacuum attainable. Some foreign particles and vapors may form sludges with the oil, impair sealing and lubrica-
tion and cause eventual seizure. A gas ballast valve is helpful in removing vapors, especially water, but it is not
equally effective on all foreign substances; therefore, periodic oil changes will vary with the particular system.
Experience with the process will help you determine the normal period of operation before an oil change is
required. SEE APPLICATION BOOKLET WITHIN MANUAL THAT PROVIDES ADDITIONAL
DETAILS ON PREVENTING OIL CONTAMINATION.
3.1c Oil Overheating
This pump designed to operate continuously below 10 Torr. Continuous operation of this pump above 10 Torr will
lead to overheating and eventual pump failure.
3.2 Oil Changes and Oil Level
3.2a Draining the Pump
An oil change is mot easily accomplished when the pump is warm and the oil is less viscous. Use a container
large enough for the oil in the particular pump. Stop the pump, and open the drain valve. A thorough job may be
accomplished by tipping the pump slightly if this is possible. The small residue remaining in the pump may be
forced out by hand-rotating the pump pulley with the exhaust port partially closed and the intake port open.
Closing the exhaust port completely under these conditions will create excessive pressure at the drain valve
which may cause the oil being drained to splatter.
3.2b Flushing the Pump
SEE APPLICATION BOOKLET WITHIN OWNER'S MANUAL THAT DESCRIBES FORCED OIL
FLUSHING PROCEDURES TO REMOVE CONTAMINANTS FROM PUMPING MECHANISM.
3.2c Refilling the Pump
After you are satisfied that the pump has been thoroughly flushed, refill the pump by puring new DIRECTORR
Gold oil into the exhaust port. Fill to the indicated level and start the pump with the intake closed. A gurgling noise
is characteristic when high pressure air is drawn through the pump. It should disappear quickly as the pressure
within the pump is reduced. If gurgling continues, add sufficient additional oil through the exhaust port until
gurgling ceases.