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6.9.4 Bearing Housings
6.9.4.1 Bearing housings shall be arranged so that bearings can be replaced without
disturbing equipment driver or mounting (see 6.9.3.1.1).
6.9.4.2 Bearing housings for oil-lubricated non-pressure-fed bearings shall be provided
with tapped and plugged, fill and drain openings at least DN 15 (1/2-14NPT ) in size. The
housings shall be equipped with constant-level sight-feed oilers at least 1,2 dl (4 fl oz) in
size, with a positive level positioner (not an external screw), heat-resistant glass
containers (not subject to sunlight- or heat-induced opacity or deterioration), and
protective wire cages. Means shall be provided such as a bulls-eye or an overfill plug, for
detecting overfilling of the housings. A permanent indication of the proper oil level shall
be accurately located and clearly marked on the outside of the bearing housing with
permanent metal tags, marks inscribed in the castings, or another durable means.
• 6.9.4.2.1 A “vented to atmosphere” constant level oiler shall be supplied, and the
bearing housing shall be vented to atmosphere. The purchaser shall specify if a particular
model of oiler is required.
NOTE The fill connection can also be used as the bearing housing vent.
• 6.9.4.2.2 If specified, a “vented to bearing housing” constant level oiler shall be
provided.
Discussion: Principal of operation of constant Level Oiler
The default for lubrication of non-pressure fed bearings (both rolling element and
sleeve) is by a sump oil bath the level of which is held by a constant-level sight–feed
oiler. The principal of operation of this type of device is outlined in Figures 6.9.4-1
through 6.9.4-6.
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Fig
6.9.4-1 (Courtesy of Trico)
Fig 6.9.4-2 (Courtesy of Trico)
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Fig 6.9.4-3 (Courtesy of Trico)
Fig 6.9.4-4 (Courtesy of Trico)
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Fig 6.9.4 – 5 (Courtesy of Trico)
Fig 6.9.4-6 (Courtesy of Trico)
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The setting of the level is determined by the position of the top adjuster arm which is
set at the center of the lowest rolling element. Once it is set, it is locked in place by the
lower adjusting arm. Refer to Figure 6.9.4-7 and 6.9.4-8. The desired oil level in Fig.
6.9.4.6 is the operating level.
An exploded view and picture of a constant level oiler is shown in Figure 6.9.4-9
Desired static
oil level
Fig 6.9.4.-7 (Courtesy of Trico)
Desired oil Level
Upper adjusting
arm position
sets level of oil
Lock Against Top
Arm
Fig 6.9.4-8 (Courtesy of Trico)
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Fig 6.9.4-9
The oil level is set by threading the top adjuster arm to the desired level (i.e center of
the lowest rolling element) and then locking in place with the lower adjuster arm. The
bottle mouth sets on this adjuster arm.
6.9.4.2.3 The oiler should be mounted on the side of the housing relative to the direction
of rotation as shown in Fig 6.9.4-10.
Fig 6.9.4-10
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Discussion: Types of Oilers
The two most common types of these devices is the “vented to atmosphere” model
Figure 6.9.4 -11 and the closed system “vented to bearing housing” oiler Fig 6.9.4 -12.
Fig 6.9.4.-11 (Courtesy of Trico)
Fig 6.9.4 -12
The vented to atmosphere model (Fig 6.9.4- 11, is the most widely used. It does not
incorporate a balance line to the bearing housing. Thus this type may not provide the
proper oil level in the housing if the housing is not vented properly. A pressure in the
housing higher than atmospheric will result in the oil level being lowered in the
housing and oil being forced back into the oiler.
In the pressure equalized “vented to bearing housing” model (Fig 6.9.4 -12) the
pressure in the oiler and bearing housing is equalized by the equalizing line. The
additional advantage of this type of oiler is that the bearing housing is essentially
sealed, and dilution of the oil due to atmospheric breathing and subsequent degrading
of the oil is reduced. This type is required when purge oil mist has been specified.
Discussion: Types of lubrication.
Rolling element bearings can be lubricated by the following methods:
a) Direct Submergence
b) Oil Ring
c) Flinger Ring
d) Oil Splash
e) Forced feed circulation
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f) Oil Mist
g) Grease
SP 6.9.4.2 describes an oil sump type of lubrication. It does not mandate how the oil is
moved to the journal or rolling elements in the bearing from the sump. In addition to
direct submersion of the rolling elements in the oil sump as described in Fig 6.9.4-13,
oil ring (Fig 6.9.4-14), flinger disc (Fig 6.9.4-15) and splash lubrication (Fig 6.9.4-16)
designs are used. The Ndm limits for this type of lubrication are listed in the Table 6.9-2
in the column headed “Oil bath or Splash Lubricated”
Discussion: Direct submergence
Direct submergence of the bearings results in churning of the oil and generation of
heat. This can increase the oil temperature and degrade the oil. It is imperative that the
oil level be accurately controlled. This churning and heat generation results in lower
speeds for direct submergence than for the other methods of lubrication.
Discussion: Oil Ring LubricationThe oil ring is made of brass or steel and sits on the
shaft. The rotation of the shaft and ring throws oil from the bath into the bearing and
housing. The housing channels oil to the bearing. The inner diameter of the oil ring is
generally 1.6 – 2.0 times the shaft diameter and may be of various cross sections such
as grooved or trapezoidal. Oil ring lubrication reduces the volume of oil to the bearing
and therefore bearing friction. The large size of the bearing housing needed for the oil
ring improves the heat transfer. Higher shaft speeds and lower oil viscosity are possible
with oil ring lubrication than the submerged design in Fig 6.9.4 -13 because of the
lower friction and better cooling.
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Discussion: Flinger Disc
Flinger
submerged in oil
Troughs
carry oil to
bearing
Fig 6.9.4 - 15
Discussion: Splash Lubrication
Fig 6.9.4-16 (Courtesy of NTN)
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In splash lubrication, the oil is splashed onto the bearings by the gears.
Discussion: Circulating Oil
Fig 6.9.4-17 (Courtesy of NTN)
In circulating oil arrangement, the oil is fed from an external source and exits the
bearing for recirculation, filtering and cooling. Fig. 6.9.4-17a bearing housing has a
sump and Fig 6.9.4-17b does not have a sump.
The Ndm limits for this type of lubrication are listed in the Table 6.9-2 in the column
headed “Circulating Oil”.
Discussion: Oil mist lubrication.
Oil Mist Lubrication is covered in 6.9.4.8
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Discussion: Grease Lubrication
Grease Fitting
Brg Housing
End Seals
Grease exit
hole
Fig 6.9.4-18 (Courtesy of SKF)
To facilitate the supply of grease, a grease fitting must be provided on the housing. If
bearing housing contact seals are used an exit hole should also be provided so that
excessive amounts of grease will not build up in the space surrounding the bearing as
this might cause an increase in bearing temperature. The exit hole should be plugged
when high pressure water is used for cleaning.
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Lubrication
groove in outer
ring
Figure 6.9.4-19 (Courtesy of SKF)
To facilitate efficient lubrication, some bearing types, e.g. spherical roller bearings are
provided with an annular groove and/or lubrication holes in the outer or inner ring
• 6.9.4.2.4 If specified, an oil sump collection container shall be provided. This container
shall be transparent and shall be located on the bottom of the oil sump to collect bearing
housing contaminants such as water. It shall be fitted with a spring loaded drain pet cock.
The collector materials of construction shall be suitable for the lubricant used.
Discussion: Illustration of sump collector container.
An oil sump collection bottles without the spring loaded drain pet cock and isolation
valve are illustrated in Fig 6.9.4 -20
Discussion: Reason for requirement and various amounts of dissolved vs free water in
LO.
This should provide a easy visual means to determine if any water is accumulating in
the bearing housing. Deterioration of the oil can also be observed by discoloration of
the oil in this collection container. Undesolved water in the oil promotes oxidation and
degrading of the base oil and additives. According to SKF “free water in the
lubricating oil decreases the life of rolling element bearings by more than 10 to 100
times”. Water also promotes corrosive attack on precision components. The following
table illustrates the relationship of dissolved and undesolved water in the oil at various
oil temperatures for an ISO 32 R&O oil.
Oil becomes cloudy at about 300-500 PPM.(Rules of Thumb)
As can be observed, as the temperature increases, the oil has a greater capability of
absorbing the water. Thus since this container is outside the bearing housing, its
temperature should be less than the oil in the housing and free water can more easily
be detected.
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Courtesy of Trico
Courtesy of Lubrication Systems
Figure 6.9.4.20
Figure 6.9.4.20 (Courtesy of Lubrication Systems – LSC)
Figure 6.9.4.21
6.9.4.3 Sufficient cooling, including an allowance for fouling, shall be provided to
maintain oil and bearing temperatures as follows, based on the specified operating
conditions and an ambient temperature of 43 °C (110 °F).
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a. For pressurized fluid film bearing systems, oil outlet temperature below 70 °C (160
°F) and bearing metal temperatures less than 93 °C (200 °F). During shop testing, and
under the most adverse specified operating conditions, the bearing oil temperature
rise shall not exceed 28 K (50 °F). [610]
Discussion: Reason for not specifying oil inlet temperature.
Discussion : Alarm and Shutdown Settings
Generally the high bearing metal temperature alarm is set around 220-230 ºF and
the shutdown at 240-250 ºF. Alternatively, after running, set the alarm at + 20 F
and + 15 above Alarm to Shut down above operating temperature. These
temperature limits are based on creep instead of actual Babbitt yield.
b. For ring-oiled or splash systems, oil sump temperature below 82 °C (180 °F).
During shop testing, the sump oil temperature rise shall not exceed 40K (70 °F) and
outer ring temperatures shall not exceed 93 °C (200 °F).[610]
c. For grease lubricated bearings, during shop testing, the outer ring temperatures
shall not exceed 93 °C (200 °F).
NOTE 1 - Machines equipped with ring-oiled or splash lubrication systems may not reach temperature
stabilization during performance tests of short duration. If the purchaser desires temperature stabilization
testing, this requirement should be stated in the inquiry and addressed by the vendor in the proposal.
NOTE 2 - If bearing temperature sensors are not supplied for ring-oil or splash systems, outer ring
temperatures can be estimated from bearing housing skin temperatures.
Discussion: Reason for modification.
API 670 defaults to the requirement that embedded temperature sensors are required
for fluid film bearings. Therefore the phrase (when bearing temperatures sensors are
supplied) has been removed from paragraph a). It has also been removed from b) since
its inclusion would make the temperature limit only apply if sensors were supplied.
6.9.4.4 For ambient conditions which exceed 43 °C (110 °F) or when the inlet oil
temperature exceeds 50 °C (120 °F), special consideration shall be given to bearing
design, oil flow, and allowable temperature rise.
6.9.4.5 Where water cooling is required, water jackets shall have only external
connections between upper and lower housing jackets and shall have neither gasketed nor
threaded connection joints which may allow water to leak into the oil reservoir. If cooling
coils (including fittings) are used, they shall be of nonferrous metallic material or
austenitic stainless steel, and shall have no internal pressure joints. Tubing or pipe shall
have a minimum wall thickness of 1,0 mm (0.040 in.) and shall be at least 12 mm (0.50
in.) outside diameter. Water jackets shall be designed to cool the oil rather than the outer
bearing ring. [610]
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NOTE - Cooling the outer ring can reduce bearing internal clearance and cause bearing failure.
[610]
Discussion: Reason for last sentence.
In some older designs, the cooling water jacket surrounded the outer race. In doing so,
the internal clearances were reduced and the bearings failed even though the bearing
housing was cool to the touch.
6.9.4.6 For equipment handling flammable or hazardous fluids, bearing housings, loadcarrying bearing housing covers and brackets between the machine’s casing or head and
the bearing housings shall be steel. Driver supports for vertical machines which utilize
thrust bearings in the driver to support the shaft shall be steel.
6.9.4.7 The bearing housing shall be equipped with replaceable labyrinth-type end seals
and deflectors where the shaft passes through the housing. Lip-type seals shall not be
used. The seals and deflectors shall be made of non-sparking materials. The design of the
seals and deflectors shall effectively retain oil in the housing and prevent entry of foreign
material into the housing. This shall be achieved without the requirement for external
service such as an air purge or grease. [610 modified].
•6.9.4.8 If specified, end seals (bearing isolators) of the axial labyrinth or magnetic-type
shall be provided.
Discussion: Discussion on bearing end seals (Bearing Isolators)
Seals, sometimes call bearing isolators, separating the bearing housing from the
atmosphere have two main functions; to prevent lubricating oil from leaking out, and
to prevent contaminants such as dust, water and dirt from entering the housing and
eventually the bearing.
The air inside the housing expands when heated during operation or during night to
day operation. During cooling, the air contracts and draws into the housing airborne
contaminants which tend to contaminate the lube oil.
Depending on the lube oil and contamination, reduction in rolling element bearing life
can range from 20- 70%Discussion: Types and illustrations of various types of bearing
isolators
These sealing devices fall into two main classifications: non-contacting and contacting.
Non contacting type seals are labyrinth and rotor/stator seals. Contacting seals are lip
and face type seals with springs or magnets.
Lip Seals: (Figure 6.9.4-18-20) Elastomeric lip seals rubbing against the shaft may
generate substantial heat and generally have a life of only 2 000 to 4 000 hours. This
life is considerably shorter than the 50 000 hour continuous service required. Lip seals
are easy to install and generally are the least expensive seals by as much as a factor of
10. When lip seals wear they allow airborn contaminents to enter the bearing through
breathing of the housing.
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Rotating Axial Labyrinth Seals: (Fig 6.9.4 -16). Rotating axial labyrinth seals are more
effective than the lip type seals. The stationary part of this type of seal is called the
stator which is pressed into the bearing housing. The rotating part of the seal is called
the rotor and is affixed to the shaft. The mating rotor and stator form a series of 90
degree turns which reduce the airborne contamination velocity and impedes it passage
into the housing. These seals still have clearances however through which the
air/contaminants can enter the housing.
Rotating Axial Labyrinth Seals fitted with dynamic O rings: (Fig 6.9.4-21). The
addition of the dynamic O ring attempts to overcome this deficiency by trying to close
this gap. During operation, centrifugal force lifts the O ring off the rotating surface,
seals the passage and prevents the O ring from rubbing on the shaft. The drawback to
this configuration is that if the O ring does not lift there will be wear.
Magnetic Closing Face Seals: (Fig 6.9.4-22, 23) To completely prevent entrance of
airborne contaminants into the bearing housing, face seals are required. Due to the
small axial space available magnetically closing face seals have been developed. These
seals have been used extensively on aircraft as pump seals, generator shaft seals and in
vertical stabilizer units. The magnets are arranged to either attract or repel to keep the
seal faces in contact. The most common arrangement is the attracting arrangement
illustrated in Figure 6.9.4-22. Figure 6.9.4-23 illustrates magnet arrangement to repel
and close the seal faces. When using magnetic seals with pure oil mist lubrication, the
seals have to be designed to be lubricated by the oil mist. For other types of bearing
lubrication, the magnetic seal faces get their lubrication from the oil mist caused by the
churning of the oil in the bearing housing. The repulsion type seals take up more axial
room than the attraction type and may not be used as often.
Examples of non contacting housing type seals are illustrated in Fig 6.9.4-16, 17 and
6.9.4-21 contact type in Fig 6.9.4-18, 19, 20, 22 & 23.
Brg.
Housing
Axial
Labyrinth
Fig 6.9.4-16
Axial Labyrinth Type Seal
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Brg,
Housing
Radial
Labyrinth
Fig 6.9.4-17
Radial Labyrinth Type Seal
For Dust
Proof
For preventing
lubricant
leakage
Fig. 6.9.4-18
Contacting Lip Type seals
Fig 6.9.4-19
Contacting V-ring seal
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Fig 6.9.4-20
Contacting Z grease seal
Rotor attached to shaft
Stationary stator
pressed into bearing
housing
O ring moves
out by
centrifugal
force during
operation
Rotor
Stator
Courtesy of Inpro Seals
Fig 6.9.4-21
Bearing protector/isolator with dynamic O-ring
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Figure 6.9.4-22
Face seal with attracting magnets (Courtesy of Isomag seals)
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Fig 6.9.4-23
Magnet seals arranged for repulsion
• 6.9.4.9 If oil mist lubrication is specified, the requirements of 6.9.4.9.1 or 6.9.4.9.2
shall apply.
Pure oil mist lubrication is used for rolling element bearings and purge oil mist is
used for either rolling element or fluid film bearings.
NOTE -
Discussion: Preferred oil mist.
Pure oil mist lubrication is preferred for rolling element bearings.
Discussion: Schematics of Pure and Purge mist systems:
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Fig 6.9.4-25
Pure Mist Application
(Courtesy of Lubrication Systems- LSC)
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Fig 6.4.9-26
Purge Mist Application
(Courtesy of Lubrication Systems- LSC)
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6.9.4.9.1 For pure oil mist lubrication, bearings and bearing housings shall meet the
requirements of a) through e) below.
a) A threaded DN 8 (1/4 – 18 NPT ) oil mist inlet connection shall be provided on the
housing or end cover for each of the spaces between the rolling element bearing or
bearing set and the bearing housing end seal.
Discussion: Typical illustration of arrangement.
A typical illustration of this arrangement is illustrated in figure 6.9-27
Collection
Bottle
Figure 6.9-27(Courtesy of Lubrication Systems- LSC)
b) Oil mist fitting connections shall be located so that oil mist will flow through rolling
element bearings. If bearing housing design is such that mist is not forced to flow through
the bearings, directional oil mist reclassifiers shall be furnished to insure oil mist
impingement on and flow through the bearings.
Discussion: Location, types and illustrations of reclassifiers.
The standard mist reclassifier is generally placed in the oil mist manifold at the
machine and is not mounted directly on the bearing housing. When located in the oil
mist manifold, it is not disturbed when the machine is removed for maintenance.
Experience has shown that if the reclassifier is mounted on the machine it can be
easily lost during the overhaul.
A directional reclassifier replaces the reclassifier in the manifold. Oil vapor particle
size is in the range of 1 – 3 microns at the input of the reclassifiers. Reclassifiers
combine these particles and discharge 10 micron sized particles.
A reclassifier is illustrated in Figure 6.9.4-28
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Figure 6.9.4-28
Reclassfier
(Courtesey of Lubrication Systems Inc)
A directional reclassifier is illustrated in Figure 6.9.4-29
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Figure 6.9.4-29
Directional Reclassifier
(Courtesy of Lubrication Systems Inc)
An oil mist arrangement at a machine and an oil mist manifold is illustrated in Figure
6.9.4-30
Oil Mist
Inlet
Used as a sump to collect o
droplets which have
coalesced in the drop piping
and prevent them from
blocking the mist outlet line
Connected to
collection container
Refer to 6.9.4-28
Figure 6.9.4-30
Oil Mist manifold at the machine (Courtesy of Lubrication Systems Inc)
Used to periodically drain
oil from the viewing
chamber through the drai
connection
c) One reclassifier shall be use for each application point.
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d) Oil rings or flingers and constant level oilers shall not be provided, and a mark
indicating the oil level is not required.
Discussion: Reason for requirement.
If installed or left in after retrofting the bearing for pure oil mist lubrication, the oil
ring will eventually wear through and fall to the bottom of the bearing housing.
e) Drain back oil passages in the bearing housing shall be plugged to prevent the oil mist
from bypassing the bearing.
Discussion: Reason for requirement.
Many bearing housing designed for oil ring lubrication have passages which allow the
oil to drain back to the sump once it has flowed through the bearing. This passage if
not plugged, will provide a means for the oil mist to bypass the bearing.
If not plugged directional reclassifiers would need to be supplied.
6.9.4.9.2 For purge oil mist lubrication, bearings and bearing housings shall meet the
requirements of a) through d) below.
a) A threaded DN 8 or DN15 (1/4-18 NPT or ½-14 NPT ) oil mist connection shall be
located in the top half of the bearing housing to act also as a vent and fill connection.
Discussion : Description and illustration of vent & fill connection.
Typically an external vent/fill assembly is screwed into this connection and this
assembly has vent and fill openings incorporated into it. The oil mist inlet channels the
oil mist to the mist penetration tube and supplies oil mist to the bearing housing. The
annular space around the penetration tube channels the oil mist to the mist outlet
connection. This arrangement allows mist flow through the housing. The mist outlet
connection is routed to the external collector as illustrated in Fig 6.9.4-31. Previously
oil mist was vented from the bearing housing and not collected. Oil mist accumulated
on the bearing and it became a housekeeping problem. This arrangement eliminates
this problem.
A vent fill assembly is illustrated in Figure 6.9.4-31
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Figure 6.9.4-31
Vent Fill Assembly
(Courtesy of Lubrication Systems Inc)
b) Constant level oilers shall be provided, and a mark indicating the oil level is required
on the bearing housing. Bearing lubrication is by a conventional oil-bath, flinger or oil
ring lubrication system.
c) Constant level sight feed oilers shall be equipped with overflow control to allow
excess coalesced oil from the mist system to drain from the bearing housing so that oil
level in the sump is maintained at proper level. The excess oil shall be contained to
prevent it from draining onto the baseplate.
Discussion: Description and illustration of requirement.
On the constant level sight feed oiler, a hole is provided which will allow the oil to drip
onto the base plate. An overflow tube should be connected to this hole to allow the
draining oil to be diverted to a collection facility.
A typical arrangement of a purge oil mist application is illustrated in Figure 6.9.4.-32
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Equalizing
line
Figure 6.9.4-32
Typical Arrangement for Purge Mist
(Courtesy of Lubrication Systems Inc)
Discussion: Reason for equalizing line on constant level oilers.
Magnetic end seals on the bearing housing and hot to cold daily operating changes the
pressure in the bearing housing and therefore need the equalizing line from the
constant level oilers
d) Constant level sight feed oilers shall be piped so that they operate at the internal
pressure of the bearing housing, do not vent excess mist at the bearing housing, or allow
oil to drip to the baseplate.
Discussion: Refer to page 68 for a description of this type of oiler and Figure 6.9.4.-28
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6.9.4.9.3 For both pure and purge mist applications, a drain connection shall be located
on the bottom of the bearing housing to provide complete oil drainage (see 6.9.4.2).
6.9.4.9.4 Shielded or sealed bearings shall not be used in conjunction with either pure or
purge oil mist systems.
Discussion: Reason for requirement.
Shield or seals on the rolling element bearing prevent the oil mist from entering the
rolling element bearing and lubricating the rolling elements and races.
6.9.4.9.5 The oil mist supply and drain fitting shall be provided by the purchaser. Unless
otherwise specified, directional reclassifiers shall be provided by the machinery
manufacturer. At process operating temperatures above 300 °C (570 °F), bearing
housings with pure oil mist lubrication may require special features to reduce heating of
the bearing races by heat transfer. Typical features are:
1. heat sink type flingers;
2. stainless steel shafts having low thermal conductivity;
3. thermal barriers;
4. fan cooling;
5. purge oil mist lubrication (in place of pure oil mist) with oil (sump) cooling. (
moved note to paragraph- note contained a provision
6.9.4.10 Housings for ring-oil-lubricated bearings shall be provided with plugged ports
positioned to allow visual inspection of the oil rings while the equipment is running.
6.9.4.11 Bearing housings shall have dimples located to facilitate consistent vibration
measurements. The dimples shall be suitable for hand-held vibration transducer with an
extension “wand”. Dimples shall be cast or machined and shall be nominally 2 mm
(0.080 in) deep with an included angle of 120 °F. (D Sales ISO)
6.9.4.12 Note to Task Force Chairman: consider one or more of the following four
paragraphs as appropriate for the individual standard.
 6.9.4.12.1 If specified, a flat surface of an agreed size and location shall be provided for
mounting of magnetic-based seismic vibration measuring equipment.
 6.9.4.12.2 If specified, bearing housings shall be prepared for permanently mounting
seismic vibration transducers in accordance with API 670.
6.9.4.12.3 Provision shall be made for mounting two radial-vibration probes adjacent to
each bearing, two axial-position probes at the thrust end, and a one-event-per-revolution
probe in each machine. The probe installation shall be as specified in API Standard 670.
6.9.4.12.4 Two radial proximity type vibration probes shall be mounted adjacent to each
bearing. Two axial position probes shall be mounted at the thrust end and a one-event-
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per-revolution probe shall be provided in each machine. The installation shall be in
accordance with API Std 670.
6.9.4.13 Bearing housings for pressure-lubricated hydrodynamic bearings shall be
arranged to minimize foaming. The drain system shall be adequate to maintain the oil and
foam level below shaft end seals.
6.9.4.14 Oil connections on bearing housings shall be in accordance with 6.4.
6.9.4.15 Bearing housings shall be Axially split and shall have a metal-to-metal joint
with cylindrical locating dowels.[617]
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[MRC]
Discussion: By specifying that angular contact bearings be a “matched pair”, the
bearings must be have the same finished dimensions to give the specified clearance or
preload. By specifying that angular contact bearings be “mounted in a paired
arrangement”, the bearings must be installed together, abutting each other, and cannot
be placed at opposite ends of a rotor or in separate bearing housings.
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Filtration: from FAG Web
site;
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