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In a new and properly installed blower there are no mov-
<br />ing contacts between the two impellers, or between the im-
<br />pellers and cylinder or headplates. Wear is then confined
<br />to the bearings which support and locate the shafts, the oil
<br />seals, and the timing gears. All are lubricated and wear
<br />should be minimal if clean oil of the correct grade is always
<br />used. Seals are subject to deterioration as well as wear, and
<br />may require replacement at varying periods.
<br />Sealing rings are designed to operate with no rubbing con-
<br />tact, once temperature and thermal growth have stabilized.
<br />The rings, which are stationary, do rub the rotating sleeves
<br />briefly during temperature cycles which result from starting
<br />and stopping the blower. However, the hardened sleeves
<br />and the sealing rings are treated with a dry lubricant coating
<br />which provides initial lubrication during break-in wear.
<br />If the sealing rings become excessively worn, greater
<br />leakage from the vents will occur. Seal rings should be
<br />replaced if vent leakage becomes excessive, or if inspection
<br />at the time of blower disassembly shows more than .010"
<br />(.25 mm) axial clearance between ring and groove.
<br />Shaft bearings have been selected to have optimum life
<br />under average conditions with proper lubrication. They are
<br />critical in the service life of the blower. Gradual bearing
<br />wear may allow a shaft position to change slightly, until rub-
<br />bing develops between impeller and cylinder or headplate,
<br />This will cause spot heating, which can be detected by feel-
<br />ing these surfaces. Sudden bearing failure is usually more
<br />serious. Since the shaft and impeller is no longer supported
<br />and properly located, extensive general damage to the
<br />blower casing and gears is likely to occur.
<br />Oil seals should be considered expendable items, to be
<br />replaced whenever drainage from the headplate vent cavi-
<br />ty becomes excessive, or when the blower is disassembled
<br />for any reason. Sealing effectiveness can vary considerably
<br />from seal to seal, and is also affected to surprising degree
<br />by shaft smoothness and freedom from scratches under the
<br />seal lip. Because of these normal variables, minor seal
<br />leakage should not be considered as indicating a need for
<br />replacement.
<br />Timing gear wear, when correct lubrication is maintained
<br />should be negligible over a period of years. Gear teeth are
<br />cut to provide the correct amount of backlash, and gears
<br />correctly mounted on the shafts will accomodate a normal
<br />amount of tooth wear without permitting contact between
<br />lobes of the two impellers.
<br />However, a high oil level will cause churning and ex-
<br />cessive heating indicated by an unusually high temperature
<br />at the bottom of the gear housing. Consequent heating of
<br />the gears will result in loss of tooth clearance or backlash,
<br />and rapid wear of the gear teeth usually will develop. Con-
<br />tinuation of this tooth wear will eventually produce impeller
<br />contacts (knocking), and from this point serious damage will
<br />be unavoidable if blower ooperation is continued. A similar
<br />situation can be produced suddenly by gear tooth fracture,
<br />which is usually brought on by sustained overloading or
<br />momentary shock loads.
<br />Operating problems may also develop from causes other
<br />than internal parts failure. Operating clearances within a
<br />blower are only, a few thousandths of an'inch. This makes
<br />it possible for impeller interferences or casing rubs to result
<br />from shifts in the blower mounting, or from changes in pip-
<br />ing support. Foreign materials sucked into the blower will
<br />also cause trouble, which can only be cured by disconnec-
<br />ting the piping and thoroughly cleaning the blower interior.
<br />If this type of trouble is experienced, and the blower is
<br />found to be clean, try removing mounting strains. Loosen
<br />blower mounting bolts and reset the leveling and drive align-
<br />ment. Then tighten mounting again, and make sure that all
<br />piping meets Blower connections accurately and squarely
<br />before reconnecting it.
<br />A wide range of causes for operating troubles are covered
<br />in the TROUBLE SHOOTING CHECKLIST. The remedies
<br />suggested there in some cases need to be performed by
<br />qualified mechanics with a good background of general ex-
<br />perience, using procedures detailed in this manual. Major
<br />repairs generally are to be considered beyond the scope of
<br />maintenance, and should be referred to the nearest Sales
<br />Office listed on the last page.
<br />Warranty failures should not be repaired at all, unless
<br />specific approval has been obtained through a Sales Office
<br />before starting work. Unauthorized disassembly within the
<br />warranty period may void the warranty.
<br />When a blower is taken out of service it may require in-
<br />ternal protection against rusting or corrosion. The need for
<br />such protection must be a matter of judgment based on ex-
<br />isting conditions as well as length of downtime. Under
<br />favorable conditions, protection will probably not be needed
<br />if shutdown is not longer than a month. Under atmospheric
<br />conditions producing rapid corrosion, the blower should be
<br />protected immediately. Simplest treatment is to spray or
<br />flush the interior with a mixture of light oil and kerosene,.
<br />making sure it reaches all surfaces. Piping should be discon-
<br />nected first, and the connections sealed after treatment.
<br />Before putting back in service, check internal condition
<br />visually and rotate the drive shaft by hand.
<br />If preferred, a commercial compound may be used instead
<br />of kerosene -oil for protection. Among suitable ones is Nox-
<br />Rust 207, marketed by Daubert Chemical Company. Best ap
<br />plied by spraying at 120°F. (491C), it may also be brushed
<br />on. Special care should be taken to insure good coverage
<br />between ends of the impellers and the headplates. After
<br />completing the application, seal all blower openings with
<br />vapor barrier paper or tape.
<br />This protection is normally effective for about one year.
<br />Before returning blower to service, inspect all internal sur-
<br />faces. If dirt of any kind is found, clean all surfaces
<br />thoroughly with a good petroleum solvent. Otherwise,
<br />blower may be connected and operated without cleaning.
<br />Be sure tape or plug is removed from vent holes near bot-
<br />tom of each headplate.
<br />It is recommended that major repairs, if needed, be per-
<br />formed at the Factory or at a Dresser Service facility.
<br />However, it is recognized that this may not always be prac-
<br />tical, especially when a spare blower is not available. If a
<br />blower is out of the warranty period, mechanical adjust
<br />ments and parts replacement may be undertaken locally at
<br />the owner's option and risk. It is recommended that Fac-
<br />tory Parts be used to insure fit and suitability. The
<br />maintenance of a small stock of on -hand spare parts can
<br />eliminate possible delays. When ordering parts give Item
<br />Numbers and their word descriptions from Figures 6 or 7
<br />and Table B. Also specify quantities wanted, and the blower
<br />size and serial number from the nameplate.
<br />Repairs or adjustments are best performed by person-
<br />nel with good mechanical experience and the ability to follow
<br />the instructions in this manual. Some operations involve ex-
<br />tra care and patience, and a degree of precision work. This
<br />is especially true in timing impellers and in handling bear-
<br />ings. Experience indicates that a high percentage of bear-
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