Welch DUOSEAL 1399B-01, Owner'S Manual

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3.40 

Repairing Oil Leaks

3.41 

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 determined 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.

3.402  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.

3.50 

Repairing Vacuum Leaks

3.501  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.

3.502  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.

3.60 

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.