• Oil Types: Recommended fluids include mineral oils (RC 90220), environmentally friendly fluids (RC 90221), and HF fluids (HFA, HFB, HFC - check seal compatibility, typically FKM for HFD; RC 90223). Specify the fluid type when ordering.
• Viscosity Range: The optimal operating viscosity range (at operating temperature) is 16 to 36 mm²/s. Absolute limits are:
  • Minimum: 10 mm²/s (short-term, max. case drain temp 90°C)
  • Maximum: 1000 mm²/s (short-term, cold start).
• Selection: Select a viscosity grade (e.g., VG 46, VG 68) so that the viscosity at the operating temperature (typically tank temperature in open circuits) falls within the optimal range. Generally, opting for a higher viscosity grade is advised.

To ensure reliable operation and long service life, the oil cleanliness should be at least NAS 1638 Class 9 or ISO/DIS 4406 18/15.

Common causes for excessive heating include:

• Internal Leakage: Excessive internal leakage within the pump components converts hydraulic energy to heat.
• Mechanical Friction: Dry or semi-dry friction due to worn parts or inadequate lubrication generates heat.
• Fluid Friction: Inadequate tank capacity or cooling, causing the system to overheat.
• Clogged Return Line Filter: A blocked return filter creates high backpressure, leading to increased temperature.
• Low Oil Level: Insufficient oil in the reservoir reduces cooling capacity.