Chemglass AF-0349 Welch Vacuum Pump - Manual (Page 18)

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Section 6: MAINTENANCE
6.01 Vacuum Problems
Inability to attain sufficient vacuum in a system is usually due to leakage, contamination, or unusual outgassing. A
system must be thoroughly clean and free from leaks to operate efficiently. If the system is found to be clean and
leak-free, but vacuum problems still exist, the pump should be checked. A simple way to test the pump is to measure
its ultimate pressure capability. This can be done by disconnecting the pump from the rest of the system and
connecting a pressure gauge directly to the pump intake. (Be sure to seal the pump intake from the atmosphere, and
be sure the gas ballast valve is closed.) The gauge can be any type that is suitable for the pressure levels expected.
Run the pump until the gauge indicates no further reduction in pressure, and compare the pressure reading to the
pump’s ultimate pressure rating.
If the pump meets its ultimate pressure specifications only when disconnected from the rest of the system, the fault
must be elsewhere in the system. If the pump’s ultimate pressure is unusually high, the pump may be badly contami-
nated, low on oil, or mechanically defective. However, if the pressure is only slightly higher than the pump’s guaran-
teed pressure, an oil change may be all that is needed to bring performance up to specifications. Be sure to use only
DIRECTORR® Premium or Gold Oil in vacuum pumps; the ultimate pressure guarantee does not apply if other types
of oil are used.
The most common cause of efficiency loss in a vacuum pump is contamination of the oil, which is usually caused by
foreign particles and/or condensed vapors. The condensate emulsifies with the oil, and when the oil is recirculated,
the condensate evaporates. The resulting vapor then reduces the ultimate vacuum attainable in the system.
Some foreign particles and vapors form sludges with the oil. The presence of sludge in the oil impairs its sealing and
lubricating properties, and eventually could cause pump seizure. Therefore, periodic oil changes are necessary to
maintain efficient operation of the system. The interval at which oil changes are required is different for each set of
operating conditions; experience will help you determine the proper interval for your system and process.
6.02 Oil Change
The best time to change the oil is when the pump is warm and the oil is less viscous. Before attempting an oil change,
the pump must be disconnected from the power outlet.
WARNING
The drain oil is hot and can cause burns.
Operating temperature of the oil is typically 140 degrees
Fahrenheit or higher. Avoid skin contact with the oil.
Changing the Oil for 8907, 8912 & 8917
To drain old oil, rotate the drain valve counter-clockwise until the handle will no longer turn. A 6-12 in. length of 3/8”
I.D. tubing can be fitted on the oil drain nipple to direct the flow of oil neatly into a bottle or other container. When the
old oil has been removed, close the drain valve by rotating it clockwise until the handle will no longer turn.
Changing the Oil for 8905, 8920 & 8925
Oil Removal: Drain the oil into a container by removing the plastic plug located below and to the left of the oil
sight glass. The pump may be tilted to remove residual oil out of the oil reservoir.