Telic Engineering / Field notes / Week 45

VSV schedule explained

Week 45Remco Petersen

Sheet 45

Field note, first posted on LinkedIn.

What the VSV schedule really does. Three-quarter front view of an LM2500 high pressure compressor with a cutaway of the variable stator vanes, actuator, VG pump and VSV schedule, six numbered points GEARBOX CONTROL VSV SCHEDULE OPEN CLOSED NGG CORRECTED FOR T2 → TOO OPEN STALL TOO CLOSED HIGH NGG 01CORRECTED SPEEDNGG corrected for T2 02VSV STAGESseven rows, move as one 03SCHEDULEclosed low, open at power 04VG PUMP + SERVOon the transfer gearbox 05TWO ACTUATORSone each side of the casing 06LVDT FEEDBACKdemand vs position

An LM2500 compressor is built for full speed. The variable stator vanes make it work at every other speed.

  1. 1.Input: gas generator speed (NGG), corrected for inlet temperature (T2). Output: VSV position.
  2. 2.Of 16 stages, seven rows are variable: the inlet guide vane row plus stages 1 to 6. LM2500+: stage 0 added, 17 stages, eight rows.
  3. 3.Closed at low corrected speed, opening as speed rises. Off schedule, too open: front stages stall. Too closed: NGG runs high for the power, towards overspeed.
  4. 4.The gearbox-driven VG pump feeds the actuators through a servo valve.
  5. 5.Each row's vanes are connected by linkages to an actuation ring. One hydraulic actuator per side moves all rings, via a master lever (LM2500) or torque shaft (LM2500+).
  6. 6.Position feedback (LVDTs on the LM2500+) is checked against demand.

How do you explain the VSVs to new operators?

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Remco Petersen
Telic Engineering B.V.
Markenplein 24, 1011 MV Amsterdam
The Netherlands
remco.petersen@telic-engineering.nl
+31 6 51345316
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