Hydraulic Oil Types: HLP, HVLP and Bio HEES Compared
Hydraulic oil is not just a lubricant, it is the power-transfer medium of the whole system. The right oil type and viscosity grade decide efficiency, wear and the service life of pump and valves. This guide compares HLP, HVLP and biodegradable HEES and shows what matters in viscosity, additives and cleanliness.
View hydraulics basicsWhich hydraulic oil types exist?
Hydraulic oils are classified by DIN 51524. HLP is the standard mineral oil with additives against wear, corrosion and ageing. HVLP adds viscosity-index improvers and stays stable across a wide temperature range. HEES denotes rapidly biodegradable oils based on synthetic esters, mandatory in water-adjacent and environmentally sensitive applications.
Which viscosity grade is the right one?
The viscosity grade (ISO VG) states the kinematic viscosity at 40 °C. Oil that is too thin increases leakage and wear, oil that is too thick raises friction and the risk of cavitation on cold start. The pump maker's specification and the system operating temperature are decisive.
- Take the pump maker's viscosity recommendation as the baseline.
- Account for both cold-start and continuous system temperature.
- For strongly varying temperatures choose HVLP with a high viscosity index.
- Keep operating viscosity in the window of roughly 16 to 36 mm²/s.
Why are cleanliness and additives decisive?
Around 70 to 80 percent of all hydraulic failures trace back to contaminated oil. The cleanliness class per ISO 4406 describes the particle load in three numbers. Fine particles act like grinding paste on pumps and valves. Additives also protect against ageing, foam and corrosion, but they deplete over time.
Hold the target cleanliness per ISO 4406 with a matching filter rating.
To the basicsFrequently asked questions
What is the difference between HLP and HVLP?
HLP is a mineral hydraulic oil with standard additives. HVLP has extra additives that raise the viscosity index, so the oil stays stable across a wider temperature range. HVLP therefore suits mobile hydraulics and strongly changing temperatures.
Can I replace HLP with biodegradable HEES?
In principle yes, but only with the system maker's approval. Ester-based HEES oils are only partly miscible with mineral oil and can attack certain seals. Before switching you must check residual oil, seals and filters and usually flush the system.
Which viscosity grade does my system need?
The pump maker's specification and the operating temperature are decisive. ISO VG 46 is the industry standard at normal indoor temperatures. For cold conditions choose ISO VG 32, for high load and heat ISO VG 68.
Find the right hydraulic oil
Our hydraulics specialists help with oil type, viscosity grade and cleanliness for your system.
Vetted selection
Recommendations from DIN 51524 and maker data.
Correct viscosity
Viscosity grade matched to pump and temperature.
Cleanliness in focus
Cleanliness class and additive care clearly explained.
Expert advice
Hydraulics specialists support your selection.