Machine Design

Study Investigates Fluid Conditioning

Commonly used conditioning methods that purify hydraulic and lubrication fluids using heat and vacuum could change the chemical and physical properties of fluids.

A study by Pall Corp., East Hills, N.Y. ( and Herguth Laboratories, Vallejo, Calif. (, examined how vacuum and temperature affect water and gas removal, and the chemical and physical properties of hydraulic and lubricating fluids.

Fluid conditioning or purification removes contaminants such as water and gases and is used with filtration to remove solid particulates from hydraulic and lubrication oils. This is a relatively straightforward and cost-effective way to extend the service life of fluids and reduce waste.

Fluid conditioning is essential in ensuring the reliability of hydraulic and lubrication systems because it enhances fluid performance and helps protect system components, says Kal Farooq, a senior staff engineer at Pall. "Water is one of the most common contaminants due to its ubiquitous nature and ability to ingress into the system. Water may be present in the base fluid in any or all of its three forms — free, emulsified, and dissolved — and each can damage the fluid and system components."

Investigators compared a range of conditioning methods, both mechanical and physio-chemical separation. Centrifuge, coalescer, and absorbent-filter methods, for example, only remove free and emulsified water. They do not remove gases or solvents. Dry-air purge, flash-distillation vacuum dehydration, and mass-transfer vacuum

dehydration remove all phases of water, gases, and solvents. However, dry-air purge is slow and requires a dry air source, and flash-distillation vacuum dehydration stresses the fluid. Mass transfer-vacuum dehydration, on the other hand, is reportedly gentler on the fluid.

The investigators used a Pall Model HNP-021 masstransfer purifier to determine effects on both additives and fluid base stock. Tests performed on samples of common hydraulic and turbine lubrication fluids covered a range of conditions, including extreme vacuum (26-in. Hg) and temperature (158°F) that mimicked typical flash distillation.

Investigations showed that the mass-transfer process operating at relatively mild conditions of 22-in. Hg and 113°F reduced water concentration to levels similar to those of more-severe flash distillation. Dissolved-air content also decreased 69% with mass transfer.

Although mass-transfer methods may be somewhat slower than those using higher heat and pressure, it does not hurt oil performance and is less likely to remove antioxidant additives, says Farooq. Higher temperatures and vacuum pressures typical of flash distillation-vacuum dehydration, on the other hand, could potentially damage the fluid. "These benefits, coupled with using less energy, translates into both time and cost savings," he says. The result is lower oil replacement and disposal expenses, as well as increased equipment uptime and reduced component replacement and maintenance.

TAGS: Hydraulics
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