Hydraulic fluid – Viscosity
Operating Viscosity Range
For optimum efficiency and service life, select an operating viscosity (at operating temperature) within the optimum range of 16 ~ 36 mm2/s
The limiting values for viscosity are as follows:
νmin = 5 mm2/s
short term (t < 3 min)
at max. perm. temperature of tmax = +115 °C.
νmax = 1,600 mm2/s
short term (t < 3 min)
at cold start (p ≤ 30 bar, n ≤ 1000 rpm, tmin = -40 °C).
Only for starting up without load. Optimum operating viscosity must be reached within approx. 15 minutes.
Example: For At an operating temperature of 60 °C, the optimum operating viscosity corresponds to the viscosity classes VG 46 or VG 68; to be selected: VG 68.
Hydraulic fluid - Types
There are several types of Hydraulic Oil in the market. The selection is usually based on application and required properties.
Mineral oil
This is the most commonly used in the market, often combined with suitable additives.
It is also known as hydraulic oil. The specifications of this hydraulic oil are set out in ISO 6743-4 with the designations HL, HM, HR, HV.
ISO-L-HL HH lubricants with oxidation reduction and anticorrosive additives
ISO-L-HM HL lubricants with wear reducing additives
ISO-L-HR HL lubricants with a high VI
ISO-L-HV HM lubricants with a high VI
ISO-L-HS Synthetic liquids
Synthetic Oil
This is recommended for heavy duty hydraulic equipment, Main features:
• Excellent protection against wear
• Excellent stability against oxidation
• Good activity against rust and corrosion
• Very good demulsification properties
• Very good deaerating and foam-suppressing properties
Flame resistant Oil
HFAE: Oil in water emulsions
• the water content is above 80% and is mixed with a mineral oil or soluble polyglycol-based concentrate
• flame resistant, can be used at temperatures between +5°C and +55°C
HFAS: synthetic concentrates dissolved in water
• No risk of separation, since this is a true solution, which means the hydraulic components are considerably more susceptible to corrosion
HFB: Water in oil emulsions
• the water content is above 40% and is mixed with a mineral oil. This emulsion is rarely used.
• flame resistant, can be used at temperatures between +5°C and +60°C.
HFC: Water glycols
• the water content is more than 35% in a polymer solution,
• flame resistant, can be used at temperatures between -20°C and +60°C.
• Can be used at pressures of 250 bar.
HFD:Synthetic liquids
• HFD-R: phosphoric esters
• HFD-S:anhydrous chlorinated hydrocarbons
• HFD-T: mixture of HFD-R and HFD-S
• HFD-U:anhydrous other composition (consisting of fatty acid esters)
• flame resistant, can be used at temperatures between -20°C and +150°C.
Biodegradable
Biodegradable hydraulic liquids are manufactured using plant oils and used in biologically critical environments (construction machinery in water protection areas, snow-grooming equipment in mountains, etc.). The fluids are class 1 harmful substances.