Chemglass AF-0350 Welch Vacuum Pump - Manual (Page 9)

Section 3: MAINTENANCE
3.1 Vacuum Problems
3.1a Pressure Determinations
Leakage, contamination and unusual outgassing are the genera causes of problems associated with poor
vacuum. To operate a 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 if given tot e 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 malfunction-
ing. 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 subject to re-evaporation during the normal cycle of pump activity this reducing the ultimate
vacuum attainable. Some foreign particles and vapors may form a sludge with the oil, impair sealing and
lubrication and cause eventual seizure. A gas ballast calve is helpful in removing vapors, especially water, but
it is not equally effective on all foreign substances; therefore, periodic oil changes are necessary to maintain
efficient operation of the system. The required frequency of changes will vary with the particular system,.
Experiences with the process will help you determine the normal period of operation before an oil change
required.
3.1c Oil Overheating
This pump is designed to operate continuously below 10 Torr. Continuous operation of this pump above 10
Torr will lead to overheating and eventual pump failure. See Section 2.3. High Pressure Operation.
3.2 Maintenance of the Model 1392 with Diffusion Pump
3.2a Determination of an Oil Change
The Model 1400 pump of the diffusion-mechanical pump combination may be repaired and maintained as
outlined in the preceding paragraphs, The pump fluid of the diffusion pump should be inspected periodically for
color change and odor. If the fluid is slightly darkened and had no odor, a simple change of fluid is normally all
that is needed. If the fluid had developed a noticeable odor, the pump should be cleaned. Follow the instruc-
tions in the Owner’s Manual for the Diffusion Pump.
3.2b Diffusion Pump Cleaning Procedures
To clean the diffusion pump, first turn off the power. Turn off the cooling fan and disconnect the power plug
after the diffusion pump has cooled. Disconnect the inlet and foreline connections. Do not scratch or damage
sealing surfaces. Remove the cold cap and jet assembly and all O-rings and gaskets. Drain oil from the
diffusion pump. Thoroughly clean the diffusion pump body interior and the jet assembly with acetone followed
by an isopropyl alcohol rinse. The inside of the pump can be dried using dry nitrogen. Install jet assembly with
he cold cap inside of the pump body. Fill the pump with 30ml of fresh diffusion pump fluid. Reinstall the pump
in the system. For more detailed information and how to replace a burned heater red instructions on the AX-
65 Diffusion Pump Instruction Manual supplied with this pump.
WARNING
Solvents, such as acetone, used to clean different pumps are extremely hazard
ous. Inhalation may be fatal or harmful. Acetone is also extremely flammable.
Never use acetone near heat or open flame. Use only in a well ventilated area.
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