Chemglass AF-0350 Welch Vacuum Pump - Manual (Page 11)

3.3c Refilling The Pump
After you are satisfied that the pump has been thoroughly flushed, refill the pump by pouring new DUOSEAL
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 pres-
sure within the pump is reduced. If gurgling continues, add sufficient additional oil through the exhaust port
until gurgling ceases.
3.4 Shaft Seal Replacement
To replace the shaft seal of a pump, drain the oil and remove the pump pulley and key. Remove the screws
securing the old seal and pry it loose with a screwdriver or similar wedge, being careful not to mar the surface
of the pump body against which the seal fits. Discard the seal and its gasket, inspect all surfaces and repair
any damages with a fine abrasive stone. Wipe all sealing areas clean and place a film of DUOSEAL oil on
both the shaft and the inside bore of the new shaft seal. Using a new gasket, carefully slide the new seal into
position and center it on the shaft. It is not necessary to apply any sealant to the gasket. Tighten the mounting
screws uniformly and refill the pump with DUOSEAL oil. Follow instructions included in repair kit.
3.5 Repairing Vacuum Leaks
3.5a Location, Cause and Effect
Oil leaks may develop wherever two mating faces are sealed with a gasket. Such seams may fail as the result
of deterioration of the gasket material, loosening of the screws caused by temperature variations, or improper
care as the result of previous reassembly. Typical gaskets seams in a mechanical pump are located at the oil
level window, the shaft seal, the oil drain, and the mating faces of such mechanical surfaces as the intake
chamber cover, the oil case, and the exhaust chamber cover. The importance of a gasketed seam is deter-
mined principally by its function. If it is a vacuum seal, the ultimate performance of the pump is dependent
upon it. If it is an oil seal, the pump may be operated satisfactorily for some time without loss of function.
Eventually, of course, a great loss of oil may cause harmful damage.
3.5b Repairing Techniques
An oil seam may be sealed by any of several methods. When an O-ring is employed, the surfaces of the O-
ring and its groove should be wiped clean. If the O-ring is not badly deformed or scratched it may be reused
by sealing with a slight film of vacuum oil or vacuum grease. Thin composition gaskets are generally used for
large irregularly shaped areas. A replacement joint of this type should be thoroughly cleaned of all previous
gasket material and the mating surfaces cleaned of any nicks.
3.6 Repairing Vacuum Leaks
3.6a Surface Preparation
Good Vacuum seals are an essential and important attribute of a good mechanical pump. A good seal is
dependent upon the quality of the mating surfaces as well as the sealant and its preparation. The mating faces
should be carefully inspected for any projections or foreign particles which might interfere with proper mating.
Slight projections such as nicks and burrs are most easily removed by rubbing with a fine abrasive stone. The
surface of the mating parts may be washed with a solvent or alcohol after which they must be thoroughly
dried.
3.6b Temporary Repair
Temporary vacuum repairs are often made by covering the known leak with an industrial sealant such as
Loctite with Teflon. Such a practice, however, is not recommended for seals of a permanent nature.
3.7 Drive Problems
If for any reason the pump will not operate, turn off the power and check the fuse and electrical connections.
Then try the power to the motor only by removing the belt. If the motor operates properly try hand-rotating
the pump in the proper direction with the pump intake port open. If both turn freely then replace the belt and
check the belt tension. The tension should be sufficient to drive the pump without visible slippage. Any
greater tension will cause noise and possible damage to the bearings of both the motor and pump. Make
certain that both pulley grooves are clean and free from oil. The pulleys must be fastened securely on their
respective shafts, and in parallel alignment.
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