Case Study

Lignum Vitae Seal Solves Turbine Seal Failures

A horizontal water turbine at Dolgeville Generating Station faced repeated failures with modern composite seals. This case study examines how a traditional Lignum Vitae seal provided a durable and long-lasting solution.

Bearing seal made with Lignum Vitae
Bearing seal made with Lignum Vitae

Background:

The horizontal water turbine “S” style at the Dolgeville Generating Station had seen numerous resin-composite style seals fail prematurely due to overheating and extensive wear.

Challenge:

  • The seal OD (working surface) is 33 11/16″ and the ID is 31 5/16″ nominal. This is the thrust face contact area. Seal nominal size 32 5/8’ Dia x 1 7/8” x 1 3/8”.
  • The seal is lubricated with dirty river water entering from the outer edge of the seal.
  • The turbine seal assembly has the thrust face mounted on the rotating component and the seal element on the stationary side.
  • The turbine runs at 327.3 RPM, seal water flow is1.25 USGPM minimum (single 3/8″ dia port). 
  • Seal pressure against wear surface is 19 psi.
  • The thrust wear surface was 304 stainless steel.
  • The turbine works on a net head of 74.50 ft, output is 6.755 MW.
  • The runaway speed is 866 rpm.

Solution:

An eight (8) segment brass backed Lignum Vitae replacement seal element and new 350 BHN polished thrust ring were manufactured to fit into the existing seal housing with some modifications to improve water flow and flow direction.

Results:

  • Successful trials with over 20 stops and starts and over 1400 hours of operation have shown very little break-in wear (<0.08”) 
  • The remaining thickness of the seal element has not changed after break-in.
  • In contrast the OEM composite seal element under the same load conditions and with the modified water supply was completely destroyed after 3 days and 6 stop start cycles.
  • The Lignum Vitae seal is still in use today after being installed in 2018
Drawing made during the design phase of the project

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Wood Grain texture taken from a Lignum Vitae tree