MTS Series 505 SilentFlo Hydraulic Power Unit Model 505-30 - Manual (Page 71)

Replacing the Pressure Line Filter Element
Model 505.20 - 505.30 SilentFlo™ HPU Accessories 71
10. If you are changing the filter because the dirty filter indicator tripped, run
the HPU for two to four hours to remove contaminants. Then take a fluid
sample and have it analyzed.
Clean or change the fluid if it does not meet an ISO cleanliness level of 13/9
or better.
11. Press the Reset button on the HPU control panel to reset any interlocks and
turn off the Dirty Filter indicator.