Viscosity must be maintained within limits at the operating temperature. Petroleum based Hydraulic oil with a
high viscosity index (95 or higher) and a viscosity grade of ISO VG 46 or 68 is optimum.
  Optimum
Viscosity, SUS
at 100 degrees F
Fluid Cleanliness
Levels ISO/DIS 4406
(SAE J1165)
 Gear Pump  200-300  19/17/14
 Piston Pump  200-300  18/16/13
 Geroller Motor  200-300  19/17/14
 Vane Motor  200-300  19/17/14
 Mobile Spool Valve    19/17/14
 Cartridge Valve    18/16/13
 The fluid cleanliness levels described can be achieved in systems with normal dirt ingression by filtering one third of the total fluid volume in the system per minute across filter media of suitable dirt holding capacity and with a pore rating of 10 micron absolute (Beta 10 equal or greater than 200).