What is the function of the zinc-free design adopted by Rexroth filter elements?

The zinc-free design of Rexroth filter elements is mainly intended to prevent zinc soap formed by the reaction between zinc and hydraulic fluid. This design avoids premature filter clogging, protects hydraulic fluid and system components, and ensures compatibility with environmentally friendly media. It is a key technology that enables the filter elements to adapt to various operating conditions.

1. Core Function: Prevent Zinc Soap Formation and Early Filter Clogging

If zinc exists in hydraulic oil (especially water-containing oil and synthetic oil), it will react with oil additives and moisture to produce zinc soap, a white gelatinous substance. Highly viscous zinc soap easily adheres to the surface of filter media, blocking pores and raising differential pressure sharply, which drastically shortens the service life of filter elements. In severe cases, a filter may fail within just a few hours. All Rexroth filter elements adopt zinc-free materials, including end caps, support frames, filter media and adhesives. This eliminates zinc soap generation fundamentally, prevents premature clogging, extends service life and maintains stable differential pressure.

2. Compatibility with Special Media to Ensure System Stability

Water-based hydraulic fluids (HFA/HFC): Such fluids contain high water content and are most likely to form zinc soap. The zinc-free design prevents blockage caused by gelatinous deposits, making it well-suited for water-based hydraulic systems used in metallurgy, coal mining and other industries.

Synthetic and ester oils: Synthetic oils feature high chemical activity and tend to react with zinc to form sediments. Zinc-free materials are compatible with a wide range of synthetic fluids and maintain the cleanliness of precision components such as servo valves and proportional valves.

Biodegradable oils: Environment-friendly rapidly degradable oils are widely used in construction machinery and agricultural equipment. Many manufacturers mandate the use of zinc-free components to prevent residual zinc from impairing the biodegradability of the fluid.

3. Protect System Components and Reduce Maintenance Costs

Prevent valve sticking: Zinc soap entering the system will block valve spools and orifices, resulting in stuck servo valves and operational malfunctions. The zinc-free design cuts down contamination and safeguards precision control components.

Prolong fluid service life: Zinc soap accelerates the oxidation and deterioration of hydraulic oil, leading to sludge and acidic substances. Zinc-free filter elements reduce fluid contamination, slow down oil aging and extend the oil change interval.