Which seal material is commonly used with phosphate ester base hydraulic fluids?

The commonly used seal material with phosphate ester-based hydraulic fluids is butyl rubber. This material is particularly suitable because it exhibits excellent resistance to chemical degradation and is compatible with the unique properties of phosphate esters. Phosphate esters can be aggressive towards many types of elastomers, leading to swelling, hardening, or premature failure. Butyl rubber has a low permeability to gases and vapors and maintains flexibility under various conditions, making it ideal for sealing applications in hydraulic systems.

In contrast, other materials like neoprene, silicone rubber, and polyurethane may not offer the same level of compatibility or resistance to the chemical composition of phosphate ester fluids. Each of these materials has specific limitations when exposed to such fluids, which can potentially cause failure in sealing applications. Therefore, butyl rubber stands out as the most effective choice for ensuring the longevity and reliability of seals in systems using phosphate ester hydraulic fluids.