Bearing Analysis · DWG LS-033

Tilting pad thrust bearing calculator

Preliminary sizing for tilting pad thrust bearings from the Waukesha MS range size tables: pick a size by thrust load (with the 60% start-up limit), shaft diameter and RPM, then check mean sliding speed, flooded or directed lubrication, supply pressure, oil temperature rise and babbitt temperature limits. Preliminary only. Waukesha asks for the final selection to be confirmed with its own program, so confirm it with the bearing maker. For radial sleeve bearings use the journal & plain bearing calculator.

Maker data (Waukesha MS size tables, Kingsbury)Last reviewed

Source: Waukesha Bearings, Modular Tilting Pad Thrust Bearings, MS range (PDF) · Kingsbury EQH thrust bearing catalog (PDF) · Kingsbury: reducing white metal temperatures

Preliminary sizing only; the maker confirms the final selection. Supply-pressure, 50 / 70 m/s and 60% start-up figures are Waukesha guidance; thrust position alarm/trip defaults are published practitioner guidance (Jackson, Vibration Institute), not a standard, and OEM/site setpoints take precedence; the rotor float formula (EPRI), pad temperature alarm offsets and the oil specific heat are rules of thumb, not API values. All 166 consistent catalog sizes are included; Series 8 size M847 is left out because its printed area, specific load and maximum load disagree.

Duty
same unit
RPM

Pick a size from your drawing or nameplate (for example M8207 = 8 pads of pad size 207) to check it against the duty, or leave on Auto.

Oil & pad temperatures
°C
°C

Some specifications cap pad metal at 115 °C (Kingsbury).

°C
Oil temperature rise Optional
SG
kJ/kg·K

About 1.9 kJ/kg·K is a typical mineral turbine oil value (rule of thumb). Use your datasheet value if you have one.

Thrust position helper Optional
mm
mm

Defaults are published practitioner guidance (Jackson, Vibration Institute), not a formal standard: alarm (warning) 15 mils (0.381 mm) and automatic shutdown (danger) 25 mils (0.635 mm), both measured “from the commissioning clear thrust active position” (Jackson, 1985, p. 84), with a 3 s delay. Replace them with your OEM or site setpoints, which take precedence.

mm

The 15 / 25 mil guidance assumes at least 30 mils (0.76 mm) of babbitt.

Method & sources
  • Size and load. Each size has a thrust area, a mean diameter, an allowable specific load (2.65–4.0 MPa) and a maximum load. The values come from the Waukesha MS brochure size tables (DHB 5A, section 10): Series 6, 8, 11, 14 and 18, and Large Series 7–12. A size fits when the normal load is at or below the maximum load, the start-up load is at or below 60% of it (Waukesha section 7, hydrostatic jacking), and the shaft is smaller than the pad bore. Waukesha’s selection chart puts pad inner diameter and maximum shaft diameter on the same axis. Confirm collar and shaft fit on the maker’s drawing.
  • Mean sliding speed V = π · Dm · N / 60. Waukesha recommends Directed Lubrication above 50 m/s and notes that offset pivots can lower pad temperature above 70 m/s. Supply pressure guidance: directed lubrication 1.4 bar preferred; a flooded housing usually runs at 0.7–1.0 bar; oil velocity in supply passages at most 3 m/s.
  • Oil temperature rise ΔT = P / (ρ · Q · cp), a steady-state heat balance in which the oil carries away all of the power loss. It is an estimate. Drain oil temperature does not tell you the pad temperature (Kingsbury).
  • Pad temperature. Kingsbury gives 130 °C (265 °F) at the 75/75 location as the whitemetal limit, notes that some specifications cap it at 115 °C, and says to estimate pad temperature when the unit load exceeds 2.8 MPa, the speed exceeds 76.2 m/s or the inlet exceeds 50 °C. Waukesha’s alternative materials run hotter than whitemetal by the amounts it states (up to +25, +40 and +120 °C), and its copper-chromium backing runs 20–25 °C cooler. Limits shown for those materials are 130 °C plus Waukesha’s figure, a derived value to confirm with the maker.
  • Oil grade. ISO VG 32 is the default: Kingsbury recommends it for moderate and high speeds and bases its catalog curves on VG 32 at a 50 °C inlet. This tool does not pick other grades.
  • Thrust position. Default alarm (warning) 15 mils (0.381 mm) and automatic shutdown (danger) 25 mils (0.635 mm), both measured “from the commissioning clear thrust active position”, with a 3 s delay, for pads with at least 30 mils (0.76 mm) of babbitt. This is published practitioner guidance (Jackson, Vibration Institute; reference point from Jackson, “Thrust and Radial Bearing Practices with Case Histories”, Proc. 14th Turbomachinery Symposium, Texas A&M, 1985, p. 84), not a formal standard. OEM or site setpoints take precedence. EPRI notes that how much wear to allow before the alarm “is more a matter of opinion than of fact, and settings might vary from one apparently identical unit to another.”
  • Rotor float, rule of thumb (EPRI). Allowable rotor float = 0.0009 × shaft diameter + 0.006 in (in mm: 0.0009 × shaft diameter + 0.15 mm). It is a rule of thumb; the machine’s internal clearances set the real end play.
  • API 670. Calls for two axial position probes per thrust bearing with 2-out-of-2 (AND) voting on the shutdown, mounted within 12 in (305 mm) of the thrust bearing. It does not set numeric alarm or trip values.
  • Not covered: power loss, oil flow and film thickness. Neither the Waukesha brochure nor this tool gives these; get them from the bearing maker. Vibration limits are also not included.

Sources