Rebuilt the power steering pump in my 94 Landcruiser today. Pump is a vaned pump. Main pump element with movable vanes spins in an elliptical chamber. Vanes move in or out depending on where they are in the ellipse. Can someone explain how this operates and the purpose of the ellipse? I've seen rubber vaned water pumps spinning in a circular chamber before and I think I understand how they work. This ellipse business has me mystified. What's the point? Variable pressure? More pressure? More power?

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13