Oil Cleanliness Requirements for Hydraulic Components

Hydraulic component manufacturers stipulate oil cleanliness levels for the hydraulic system in order for their components to have adequate life. The hydraulic system’s cleanliness level should be at least as clean as the lowest required ISO code level. In other words, the “lowest” required level is the most strict cleanliness requirement. The following are a few typical ISO code cleanliness levels required by some representative hydraulic components in a hydraulic system:

Gear Pumps 19/17/15
Vane Pumps 18/16/14
Piston Pumps 17/15/13
Directional Valves 20/18/15
Proportional Valves 18/16/13
Servo Valves 16/14/11

Since the cleanliness level of the hydraulic system dramatically affects the life of the various system components, a new industry trend is to take the duty cycle, operating pressure and system reliability requirements into consideration. When the operating pressure is higher than 3000 psi, the duty cycle is severe, or the system reliability is important, then the ISO cleanliness level code is reduced by one digit for each of the 3 levels of contamination size and concentration. For example, a piston pump system (normally 17/15/13) operating at 3000 psi but with continuous severe operation would require a recommended ISO cleanliness level of 16/14/12 to ensure adequate component life.