The BMP 851 uses a closed-loop hydrostatic circuit for drum drive and an open-loop circuit for vibration and steering.
The manual assumes run-time, but high-vibration applications degrade oil faster. Change hydraulic oil every 150 hours if compacting reinforced concrete rubble. service manual for bomag bmp851
Based on the official service training documentation, the manual provides: The BMP 851 uses a closed-loop hydrostatic circuit
Inspect, clean, or replace the filter element depending on site conditions. the manual provides: Inspect