Howden Roots 412 HPT, Installation, Operation & Maintenance Manual

9

ISRB-2009, Rev. 02_17.

Inspection & Maintenance

A good program of consistent inspection and maintenance 

is the most reliable method of minimizing repairs to a blower. 

A simple record of services and dates will help keep this 

work on a regular schedule. Basic service needs are:
•  Lubrication
•  Checking for hot spots
•  Checking for increases or changes in vibration  

and noise

•  Recording of operating pressures and temperatures

Above all, a blower must be operated within its specified 

rating limits, to obtain satisfactory service life.
A newly installed blower should be checked often during 

the first month of full-time operation. Attention there after 

may be less frequent assuming satisfactory performance. 

Lubrication is normally the most important consideration and 

weekly checks of lubricant levels in the gearbox and  

bearing reservoirs should be customary. Complete oil 

change schedules are discussed under 

LUBRICATION

.

Driver lubrication practices should be in accordance with the 

manufacturer’s instructions. If direct connected to the blower 

through a lubricated type coupling, the coupling should be 

checked and greased each time blower oil is changed. This 

will help reduce wear and prevent unnecessary vibration. 
In a new, and properly installed, unit there is no contact 

between the two impellers, or between the impellers and 

cylinder or headplates. Except for impeller strips, which 

are intended to wear as necessary as blower tempera-

ture rise increases, this wear should be minimal if do not 

exceed maximum blower operating temperature riseWear 

is confined to the bearings (which support and locate the 

shafts) the oil seals, and the timing gears. All are lubricated 

and wear should be minimal if clean oil of the correct grade 

is always used. Seals are subject to deterioration and wear, 

and may require replacement at varying periods.
Piston ring seals (28) are designed to operate without  

rubbing contact, once temperature and thermal growth  

have stabilized. The stationary rings will rub the rotating 

sleeve (38) briefly as a result of temperature cycles that 

occur during the startup and shutdown of the unit.  

The sleeves are hardened and the rings are coated with  

dry lubricant that provides for temporary break in wear. 

Replace piston ring seals if they become excessively worn.
Shaft bearings are designed for optimum life under  

average conditions with proper lubrication and are critical  

to the service life of the blower. Gradual bearing wear may 

allow a shaft position to change slightly, until rubbing  

develops between impeller and casing. This will cause  

spot heating, which can be detected by observing these 

surfaces. Sudden bearing failure is usually more serious. 

Since the shaft and impeller are no longer supported and 

properly located, extensive general damage to the blower 

casing and gears is likely to occur.

Oil seals should be considered expendable items, to be 

replaced whenever drainage from the headplate vent cavity 

becomes excessive or when the blower is disassembled for 

any reason. Some oil seal leakage may occur since an oil 

film under the lip is required for proper operation. 

Periodically leaked oil should be wiped off from surfaces. 

Minor seal weepage should not be considered as  

indicating seal replacement.
Timing gear wear, when correct lubrication is maintained, 

should be negligible. Gear teeth are cut to provide the 

correct amount of backlash, and gears correctly mounted 

on the shafts will accommodate a normal amount of tooth 

wear without permitting contact between lobes of the two 

impellers. However, too high an oil level will cause churning 

and excessive heating. This is indicated by unusually high 

temperature at the bottom of the gear housing. Consequent 

heating of the gears will result in loss of tooth-clearance , 

backlash and rapid wear of the gear teeth usually will de-

velop. Continuation of this tooth wear will eventually produce 

impeller contacts (knocking), and from this point serious 

damage will be unavoidable if blower operation is continued. 

A similar situation can be produced suddenly by gear tooth 

fracture, which is usually brought on by sustained overload-

ing or momentary shock loads.
Problems may also develop from causes other than internal 

parts failure. Operating clearances within a blower are only 

a few thousandths of an inch. This makes it possible for 

impeller interferences or casing rubs to result from shifts in 

the blower mounting, or from changes in piping support. If 

this type of trouble is experienced, and the blower is found 

to be clean, try removing mounting strains. Loosen blower 

mounting bolts and reset the leveling and drive alignment. 

Then tighten mounting again, and make sure that all piping 

meets blower connections accurately and squarely Foreign 

materials sucked into the blower will also cause trouble, 

which can only be cured by disconnecting the piping and 

thoroughly cleaning the blower interior.
A wide range of causes & solutions for operating troubles 

are covered in the 

TROUBLE SHOOTING CHECKLIST

. 

The remedies suggested should be performed by qualified 

mechanics with a good background. Major repairs generally 

are to be considered beyond the scope of maintenance, and 

should be referred to your authorized Roots distributor.
Warranty failures should not be repaired at all, unless spe-

cific approval has been obtained through a Sales Office or 

the factory before starting work. Unauthorized disassembly 

within the warranty period may void the warranty.