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Which Hydraulic Oil to use in my power pack?

There are a wide range of choices over an even wider range of budgets, but the right hydraulic oil will prolong your machine life and reduce your overall running costs.

Three initial questions must be answered:-

1) In what type of equipment will the hydraulic fluid be used?
2) How severe will the duty be?
3) What operating temperature and pressures will be experienced?
4) Environment food safe etc

Environment food safe etc

Answers to these questions will lead to the primary choices of viscosity grade (VG) and hydraulic fluid types.

In what type of equipment will the hydraulic oils be used?

Selection of a hydraulic fluid with a viscosity that bests suits the system pump is a good place to start. Manufacturers will normally specify a range of oil viscosity. These will vary dependent upon the pump type. Vane pumps typically require 14-160 cSt, Piston pumps are more durable than a vane pump and require 10-160cSt. Gear pumps are the most tolerant to contamination and a conservative range would be 10-300cSt. Industrial machinery is typically designed to operate within a cleaner more stable environment, where outdoor and mobile applications will more likely have severe temperature variations, higher humidity and more demanding duty cycles.

How severe will the duty be?

Duty would normally be described by running time, environmental factors, likelihood of contamination ingress, maintenance arrangements etc.

Examples of Low/Medium/Heavy Duty would be:-

  Light Medium Heavy
Run time < 2hours >2 hours > 24 hours
Humidity <70% >70% >90%
Dirt Clean Room Industrial (factory) Agricultural
Maintenance Regular Irregular Never

Heavier duty demands will normally lead to the use of a mineral oil with a good additive package (such as a HVLP) to improve performance or the selection of a fully synthetic oil.

For hydraulic systems with high running times a fluid with a high viscosity index (VI>130) will avoid damage and breakdowns as it extends lifetime of hydraulic pumps and components.  

What operating temperature and pressures will be experienced?

Where temperature extremes are large (below -5oC and above +60oC) and pressures above 250 bar the use of a fluid with a good mix of additives will be important. Mineral based oils (HM/HLP) will be sufficient in the most common applications as these often have anti-wear additives, oxidisation inhibitors and viscosity improvers. Fully synthetic oils will however out-perform mineral hydraulic oil ensuring that the viscosity and lubricity remains stable over a longer period.

Viscosity Grade (VG)

A hydraulic fluid has a low viscosity when it is thin and a high viscosity grade when it is thick. The viscosity reduces as the temperature rises and visa-versa. The hydraulic fluid must be thin enough to flow through the filter, inlet and return pipes without too much resistance. On the other hand, the hydraulic fluid must not be too thin, in order to avoid wear due to lack of lubrication and to keep internal leakage within limits. Viscosity grade is expressed at 40oC eg ISO46 which is an oil with a viscosity of 46 cSt measured at 40oC.

According to DINISO 2909 oil viscosity changes versus temperature, Viscosity Index (VI), is normally between 90-110. VI above 130 are largely insensitive to temperature change.

A viscosity range of 12-80sCt  is recommended for a large range of commercially used hydraulic equipment.

Hydraulic oil specifications

Hydraulic power packs can be used with a wide range of hydraulic oil grades, commonly:-

· Hydraulic Oil (ISO11158-HM) – Mineral based – hydraulic oil grades widely used in light duty  applications where temperature and pressures are moderate.

· Hydraulic Oil (DIN51524-2-HLP) – Mineral based with additives for oxidation, corrosion and wear protection. Used for general applications where temperature and viscosity conditions are observed.

· Hydraulic Oil (51524-3-HVLP) – Premium grade mineral based as per HLP but with improved viscosity temperature behaviour (VI>140).

· Biodegradable hydraulic oil – HETG, HEPG, HEES and HEPR – A developing technology and is yet to replace mineral oils in all applications. Storage and service life is limited, particularly at elevated temperatures.

· Fire Resistant Fluids (ISO12922 – HFA, HFB, HFC and HFD) – HFA,HFB and HFC contain water solutions and must only be used with specifically designed products. Not suitable for systems containing aluminium and some paint products. Seal compatibility must be checked.

For Hydraproducts powerpacks we recommend the following:-

  Light duty Medium duty Heavy duty
HPU and HPR Micro powerpacks HM 32 HM32 HVLP32
HPM Mini packs HM32 HLP32 HVLP32
HPS Standard Hydraulic power units HM32 HLP32 HVLP32
Bespoke systems HLP32 HVLP32 HVLP32

Some sources of these oils would be:-

HM32 – Shell Hydrau HM32 – Castrol Hyspin VG32

HLP32 – Shell Tellus 32 – Castol Hyspin AWS32

HVLP32 – Shell Tellus S3V 32 – Castrol Hyspin HVI 32

Where environmentally sensitive fluids are required the use of Castrol Carelube HES32 can be employed in all our products, for light and medium duty ONLY.

Where a small level of fire resistance desirable then the use of a Castrol Anvol SWX FM HFDU fluid may be implemented in all of our products, for light and medium duty ONLY. 


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