![]() You come about terms like absolute viscosity, dynamic viscosity, kinematic viscosity, poise (as /pwaz/), stokes. Done!īut if you dig" a bit deeper, and curious tech always like digging deeper - a lot of questions arise, and there aren't many "feet on the ground" answers. For example, here, in Portugal, I would choose 32 for hand pumps and equipment that works cold, 46 for "normal" hydraulics, and 68 for mobile stuff that runs at slightly higher temperatures. Practice shows that for a given range of machinery in a given region two or three oil types will cover all the bases. You'll be OK and your oil viscosity choices (or recommendations) will be sound. Practically speaking - you don't need to know more, really. ![]() The oil viscosity choice, therefore, will depend on a) the temperatures the piece of equipment will be facing during its operation cycles and b) the viscosity recommendations for the components used in the system, with 25 being the universal "bullseye" in 99.9% of cases. ![]() The high-temperature stuff "thins out" to a lesser degree. Oil gets "thinner" as the temperature rises, and there are "normal" oils and "high-temperature" oils. The numbers correspond to "centistokes" (whatever this means) at 40 Cº. You get to choose from a set of standard universally accepted viscosity grades like 32, 46, 68, etc., where a bigger number means "thicker" oil. It is very important - choose it wrong and your hydraulic goes kaboom. Let us consider for a moment the simple stuff every tech knows about the viscosity of hydraulic oil: I bet all of my readers understand what the word viscosity means and know by heart the viscosity ranges of the hydraulic oil their equipment operates with, and in this regard, I won't be telling anything new, but I want to dive a bit deeper into this topic, and I if you finish this post - you'll never look at the term "viscosity" the same way as before, and will never be intimated or confused by phrases like mm squared per second, pascal-seconds, and even momentum diffusivity. The viscosity of crude oils can be measured using a standard method (ASTM D2983).Today I will be talking about the viscosity of hydraulic oil. However, different reference temperatures, such as 40☌ (104 ☏), 50 ☌ (122 ☏), and 60 ☌(140 ☏), are also used to report kinematic viscosities of petroleum fractions. Values of kinematic viscosity for pure liquid hydrocarbons are usually measured and reported at two reference temperatures, 38☌ (100☏) and 99☌ (210☏) in cSt. Kinematic viscosity is expressed in units of centistokes (cSt), Saybolt Universal seconds (SUS), and Saybolt Furol seconds (SFS). Viscosity of liquids is usually measured in terms of kinematic viscosity, which is defined as the ratio of absolute (dynamic) viscosity to absolute density (ν = μ/ρ). ![]() Among petroleum products, viscosity constitutes a critically important characteristic of lubricating engine oils. Interestingly, the viscosity of liquid decreases with increasing temperature, while viscosity of gases increases with increasing temperature. Power requirement to transport (e.g., to pump) a fluid depends strongly on the fluid’s viscosity. Newton’s Law of Viscosity provides a physical definition of viscosity. A high-viscosity fluid has a low tendency to flow, whereas low-viscosity fluids flow easily. Viscosity, commonly depicted by the symbol μ, is a physical property of a fluid that describes its tendency/resistance to flow.
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