Edwards, Stokes, Microvac 412H11, Piston Vacuum Pump Stokes Microvac 412H11 Piston Vacuum Pump. INSTRUCTIONS PART I Section Page 1. DESCRIPTION . into vapor again as the oil circulates into high vacuum in the pump cylinder limiting the vacuum to the Vapor pressure 2 3 Olt;JAL VOLTAGE COIL CONNECTiONS WI183;TH 11511.,50/60 CY.,IPH. . CONTIIOL L2 1 230V. 460 V.