What does "ashless" mean in ashless anti-wear hydraulic oil?

The additive system of anti-wear hydraulic oil is divided into ash (zinc) formula and ash free formula.

The grey type is: zinc containing main agent ZDDP zinc dialkyl dithiophosphate, and its standard is bounded by the zinc content of 0.03% in the oil.

The ashless type is zinc free.

The advantage of ashless type is that it does not contain zinc and will not react with silver parts. Because many parts, such as valves, are made of silver plated materials, zinc will be electroplated with silver, replacing silver and damaging parts. Ashless hydraulic oil will not corrode copper parts and is more suitable for plunger pumps with copper or copper alloy parts. It has good oxidation resistance and rust resistance, greatly reduces oil sludge and acidic substances, ensures system cleanness, reduces faults and prolongs the service life of oil products.

There is no ash produced during the use of the oil and does not react with silver parts. Ashless hydraulic oil is also called silver resistant hydraulic oil.