Silvery particles in hydraulic oil that are over 40µ in size, if they can be seen with the naked eye, are indeed not always iron. These "silver fish" can also have one of the following causes:
- They may be aluminum particles from pump housings or abrasion from pistons or cylinders.
- Tin has come off a plain bearing running surface or guide.
- Zinc has flaked off from galvanized elements such as the filter support core or tank coating.
- Nickel has come off filter end caps or electroplated coatings.
- Chrome-plated components such as piston rods are visible as chips due to wear.
A more definitive statement can be made on the basis of an oil analysis. With this, the cause of this silvery wear can usually be determined quickly and hopefully eliminated in time.