37-1-614 Page 29
ROTOR SHAFT SEALS
– Rotors have a labyrinth type shaft air seal to minimize air leakage along the
shaft from the compression chamber. More air will leak through the seals at the discharge end since they
are under higher air pressure. Excessive air leakage indicates shaft seal failure.
The air seal consists of two parts, a hardened steel bearing spacer with grooves cut into the outside
diameter, and a steel-backed babbitt ring (shaft seal) pressed into the bearing carrier. The grooved end
of the spacer and the shaft seal bore have a close fit when cold. When the blower reaches operating
temperature for the first time, the babbitt embeds slightly into the grooves, forming a close running fit to
control air leakage along shaft. No maintenance is required, except that bearing carrier removal usually
will destroy the babbitt grooving and the shaft seal must be replaced. Shaft seals that have been in
operation should not be reused as excessive leakage may result. The bearing spacer can be reused
unless damaged. After installation of new seals, rotation of the blower may be tight for a few turns until
bearing spacer grooves cut running ways into the babbitt. For seal replacement refer to Disassembly
Section, page 36, and Assembly Section, page 40.
BEARING OIL SEALS
– Oil leakage along each shaft from the oil sumps is prevented by a hydrodynamic
lip type seal pressed into the bearing carrier. These seals are unidirectional lip seals. The hydrodynamic
spiral in the Teflon lip pumps the oil back into the sump. Usual causes of seal failure are: high
temperature, rough surface on bearing spacer, damage during installation, and improper seal used. The
radius at the end of the bearing spacer and O.D. should be highly polished to prevent seal lip damage
during installation. Use only seals shown in parts list as they have been selected for blower service.
They must be installed in the correct location and with the proper orientation or the oil will be pumped out
of the blower. Rotation arrows and color coding are used to distinguish clockwise seals from
counterclockwise seals,
see Figure 7-13, page 44.
PERIODIC INSPECTIONS
– A well-organized maintenance program will provide for periodic inspection of
the blower, drive and components. These inspections may prevent major repair and downtime.
1.
Observe the blower for vibration, heating, noise, oil seal leaks, and excessive shaft air leaks.
2.
Check for proper operation of the filters, coupling, drive, power unit, relief and check valves,
gauges and other controls.
3.
Disconnect the drive and turn the blower by hand to check for drag, tight spots, bearing wear
(radial and axial) and gear backlash. Rotation should be free with no indication of drag or
metallic interference.
4.
Inspect the interior through the inlet or discharge port for cleanliness, corrosion or parts
contact.
Rotating components will cause severe injury in case of personal contact. Keep hands away
from the blower inlet and discharge ports.
5.
Check tightness of all screws and bolts.
SOME COMMON CAUSES OF BLOWER FAILURE
1.
Poor air filter maintenance or incorrect selection.
2.
Inadequate lubrication (wrong, dirty or low oil).
3.
Backflow of materials into the blower.
4.
Discharge pressure or inlet vacuum above blower rating.
5.
Blower speed below minimum rating.
6.
Blower speed too low for discharge pressure or inlet vacuum.
