Toll Free (800) 363-8571


TRI Transmission and Bearing Corp. manufactures replacement and repairs pressure dam bearings for Gyrol style fluid drives. Our bearings are steel backed and Babbitt lined. Please call (610) 363-8570 or use our online form to contact TRI for pricing and delivery.

 Product Selection - Bearings - Pressure Dam Bearings

Pressure Dam Bearings for Fluid Drives
Part Identification Table

SC = Single Circuit | DC = Dual Circuit | CW = Clockwise rotation | CCW = Counter-clockwise rotation 
Rotation is determined as viewed from the input end

  Fluid Drive
Size 198 SC CW
Fluid Drive
Size 198 SC CCW
Fluid Drive
Size 212 SC CW
Fluid Drive
Size 212 SC CCW
Input-Outboard Bearing 110-01 110-02 110-04 110-03
Input-Inboard Bearing 110-02 110-01 110-02 110-04
Output-Inboard Bearing 110-01 110-02 110-04 110-03
Output-Outboard Bearing 110-02 110-01 110-03 110-04

  Fluid Drive
Size 250 SC CW
Fluid Drive
Size 250 SC CCW

Fluid Drive
Size 270 SC CW
Fluid Drive
Size 270 SC CCW
Input-Outboard Bearing 110-06 110-03 110-06 110-05
Input-Inboard Bearing 110-05 110-06 110-05 110-06
Output-Inboard Bearing 110-05 110-06 110-05 110-06
Output-Outboard Bearing 110-06 110-05 110-06 110-05

  Fluid Drive
Size 250 DC CW
Fluid Drive
Size 250 DC CCW
Fluid Drive
Size 270 DC CW

Fluid Drive
Size 270 DC CCW
Input-Outboard Bearing 110-08 110-07 110-08 110-07
Input-Inboard Bearing 110-09 110-10 110-09 110-10
Output-Inboard Bearing 110-07 110-08 110-07 110-08
Output-Outboard Bearing 110-08 110-07 110-08 110-07

Call (610) 363-8570 or use the online form
to contact TRI for pricing and delivery


Information about Pressure Dam Bearing for Fluid Drives

The Pressure-dam Bearing design is a variation of a Babbitted circular bore bearing, and is used to provide a downward force on the journal.  The objective of this downward force on the journal is to increase the loading of the journal on the lower bearing film at operating speed, with the intent to suppress sub-synchronous rotor vibration and/or to reduce rotor vibration amplitudes due to unbalance conditions of the rotor.  

A pressure-dam bearing is made as a circular bore bearing with the upper arc having a shallow groove milled in it that begins at the oil spreader groove on the upcoming side and extends in the direction of rotation for 100 degrees to 135 degrees, as selected by the designer. The axial length and depth of this shallow groove are two additional parameters that the designer has available to obtain the downward force on the journal that is desirable for the specific application.  Other design features available to the designer are the overall length of the bearing bore and the use of any grooving in the lower half to help to control rotor vibrations, particularly sub-synchronous rotor vibrations.  

TRI uses steel-backed bearings to provide improved control of the diametral clearance between the journal and the bearing as a function of temperature change from cold assembly conditions to hot operating conditions.  With a bronze backing, the diametral clearance increases with increasing temperature, but with steel backing, the housing, bearing backing, and shaft are all steel and there is very little clearance change as operating temperature changes.  The overall benefit of steel-backed bearings is that smaller clearances can be maintained in all operating temperature conditions with a corresponding improvement (reduction) in rotor vibration amplitudes.

Pressure-dam bearings are more susceptible to high amplitude rotor vibrations than certain other bearing designs for this reason:  The upper half has the central shallow groove with two lands adjacent to the groove.  These lands act as seals to restrict the oil flow out of the central groove, and this restriction is what causes a high pressure to develop in this groove at the end where the groove stops, which is called the "dam".  If the journal rubs these seals and erodes them, the restrictive sealing effect is reduced and this reduces the pressure that is created in the groove.  This reduction of pressure leads to reduced downward force on the journal which in turn leads to increased amplitude of vibration and increased likelihood of more erosion and reduced downward force, and the degradation continues until such time that the vibration amplitudes increase to the point that the vibration monitoring instrumentation reaches an alarm level and an operator takes the unit out of service.  

Misalignment conditions that cause the journal to rub the top of the bearing can also contribute to similar results.

Almost all Gyrol style fluid drives installed prior to approximately 1980 did not have any effective vibration instrumentation.  Indeed, many still in service today do not have a full set of proximity vibration instrumentation probes in place, with the consequence that it is likely that these fluid drives can experience bearing damage, severe rotor vibrations and other consequential damage without detection by the operators.