Welch Vacuum 1400 Duoseal Belt Drive - Manual (Page 9)

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Section 3: MAINTENANCE
3.10 Vacuum Problems
3.101 Pressure Determinations
Leakage, contamination and unusual outgassing are the general causes of problems associated with
poor vacuum. To operate at maximum effi ciency 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 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.
3.102 Oil Contamination
The most common cause of a loss in effi ciency in a mechanical pump is contamination of oil. It is
caused by condensation of vapors and by foreign particles. The undesirable condensate emulsifi es
with the oil which is recirculated and subject to re-evaporation during the normal cycle of pump activity
thus 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 effi cient 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 is required.
3.103 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 2.21, High Pressure
Operation.
WARNING
Solvents, such as acetone, used to clean different pumps are
extremely hazardous. Inhalation may be fatal or harmful. Acetone
is also extremely fl ammable. Never use acetone near heat or open
fl ame. Use only in a well ventilated area.
3.20 Oil Changes and Oil Level
3.201 Developing a Maintenance Schedule
After studying many examples of pump failure, Welch has found the most common reason is poor
condition of the oil. This is why a regular maintenance schedule for the oil is critical to obtain the
longest service life out of your DUOSEAL pump. Welch recommends that you examine the condition
of the oil on a daily basis in the early days of a new process or experiment. You want to look for
discoloration of the oil and whether the oil level is rising. The discoloration can indicate deterioration
of the oil and a rising oil level can indicate condensation of vapors is occurring in the pump. When
changes occur, the oil needs to be change. If no changes in the oil level or color are observed,
extended pump service life is obtained if the oil is changed every three to four months.
3.202 Forced Oil Flushing
When you drain oil through the drain valve, you are not removing the oil and contaminants that are
inside the pumping mechanism. You are removing oil only from the oil case. Welch recommends
a forced oil fl ush of DUOSEAL pumps be performed at the regular maintenance oil change. The
procedure for the forced oil fl ush is given below.