Phosphate Ester fluids are commonly found in fire resistant fluids, but how should they be used?

Phosphate Ester fluids were only discovered in the 1940’s, but since then their usage has seen a steady growth as a result of their fire and wear resistant properties

The first commercial products were synthesized from coal-tar derivatives and were consequently composed of a mixture of various isomeric aryl phosphates, including the neurotoxic orthotolyl phosphate. Today, other raw materials are used for the synthesis of phosphate esters. Modern technology
affects better control of the manufacturing process, and the toxicity of the final product is normally low.

Phosphate esters are used primarily as fire-resistant basestocks in several applications including hydraulic systems, turbines and compressors.

In addition to outstanding fire-resistant properties, phosphate ester fluids are thermally stable, have low volatility and excellent boundary lubrication properties.

The downside is poor hydrolytic stability; phosphate esters decompose in the presence of sufficient water. They also have compatibility issues with many common seal materials (Buna-N, nitrile) and paints.

Phosphate Ester Fluids Used As Fire-Resistant Fluids.

Phosphate esters are the most fire resistant of the non-aqueous synthetic basestocks in common use. Their high ignition temperatures, excellent oxidation stability and very low vapor pressures make them difficult to burn, while also having excelent self-extinguishing properties.

Numerous organic phosphorus compounds including phosphites, phosphonates and phosphates have found application as additives in a variety of lubricant formulations as stabilizers, anti-wear additives, antioxidants, metal passivators and extreme-pressure additives. Of these, zinc dialkyl dithiophosphates (ZDDP), found in virtually all automotive engine lubricants, are the most widely used.

However only one group of phosphates, the tri-substituted natural esters of H3PO4, has found significant use as a synthetic basestock.

Why Are Phosphate Ester Fluids Common In Hydraulic Applications.

The use of phosphate ester-based products in hydraulic applications is still principally dictated by fire-risk considerations.

Although inhibited phosphate esters possess excellent oxidation stability and inherently good anti-wear properties under critical loading conditions, they suffer from somewhat inferior hydrolytic stability, low viscosity index and extreme chemical aggressiveness toward many conventional seal and coating materials.

These weaknesses limit the use of phosphate ester to specialized applications where a high degree of fire resistance is required.

Using Phosphate Ester Fluids Requires Higher Maintenance.

The user of fire-resistant fluids must accept the need for greater vigilance with respect to fluid maintenance than is normal for conventional mineral fluids. No longer is it sufficient to periodically change filters, repair the occasional leak and top off the reservoir. On average, phosphate esters cost five times more than their mineral counterparts.

The majority of phosphate Ester fluids display a considerably greater degree of detergency than mineral fluids. Consequently, dirt particles or wear debris do not settle out in the sump as readily. This tendency promotes abrasive wear of pumps and other components along with affecting valve function.

If you’re in doubt about whether phosphate Ester fluids are the right choice, call the professionals at Habot Synthetic Lubricants. We have quality fluids and lubricants to meet the most demanding operating conditions.