The oil filtration rate selection


  • Fluid Cleanliness Standards
  • Recommendations for cleanliness class for your system
  • Recommendations for Locations of Filters at your system

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There are a lot of different standards for the classification of solid particle contamination in lubrication and hydraulic fluids: ISO 4406/1999, NAS 1638, SAE AS4059, GOST 17216-2001, etc.

To determine the cleanliness level by  ISO 4406/1999 the solid particles present in 100 ml fluid are counted, sorted according to size & quantity and classified into particle ranges, defined by two (Microscopic counting) or three (automatic particle counter) numbers divided by slashes:

Hydraulic oil viscosity


  • Dynamic and kinematic viscosity in SI and British unit
  • Understanding the optimum operating viscosity range
  • Selecting the  ISO VG (Viscosity Grade) for your system
  • Understanding the Viscosity Index

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The viscosity is a measure of the fluid’s resistance to flow.

There are dynamic and kinematic viscosity are usually common for calculations.

The symbol for dynamic viscosity is the Greek letter mu (µ). The SI unit for dynamic viscosity is the pascal-second (Pa·s), but the more common unit is the centipoise (cP):

1 P = 0.1 Pa·s
1 cP = 0.001 Pa·s = 0.001 N·s/m2.

For example, the dynamic viscosity of water at 20°C is 1.00 cP

Cylinder’s Area Ratio


  • Understanding the Cylinder Area Ratio

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By the definition, the “Cylinder Area Ratio” is the relation between the complete area of the bore and the same area minus the area of the rod:

 CR = \frac{A_b}{A_b - A_r}


For the ratio there is important a diameter of the rod (but not rod side annular area!) because when you choose the cylinders for your project in hydraulic catalogs you pick out them using Piston and Rod diameters.

This is why the area ratio CR is always >1.

Sometimes, you can meet records like:

 \frac{A_b}{A_b - A_r} : 1

For example, for cylinder 4″ bore diameter and 2.5″ rod diameter, the ratio is:


So, CR=1.64 or 1.64:1

Hydraulic manifolds material


  • Selecting the type of material for manifold
  • Manifold’s Blackening

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Choosing between ductile steel and aluminum can mean the difference between a failed product or machine and a reliable, productive machine. Consider the following factors:

System Pressures
When system pressure will be consistently above 3500 psi, ductile steel is required. Also, when normal operating pressures are at or near or at 3500 psi, and when pressure “spikes” might exceed 3500 psi, ductile steel should be considered.