We have GE-BHEL supplied Frame-VI Gas turbines. Frequently, we are facing problem with increase in hydraulic oil filter DP and consequent drop in hydraulic oil pressure. Hydraulic oil pressure dropped from 85 Kg/Cm2 to 76 Kg/Cm2 for the filter DP of 3.6 Kg/Cm2. Oil quality is analysed and filter dust is found at 1.15 mg/100ml. Can somebody explain what are the probable reasons for increase in hydraulic oil filters DP and what are the limits for filter dust in lube oil?