Maintaining clean hydraulic fluid is crucial to keeping mobile equipment in good health — and keeping it up and running longer at peak operating performance.

A good way to ensure clean hydraulic fluid is to perform routine fluid analysis checks, which detect the fluid contaminants that cause up to 80% of hydraulic system failures. Some hydraulic component manufacturers are equipped with ISO-certified labs that provide fluid testing and diagnostic services for their customers.

A hydraulic blood test
Fluid testing labs are high-tech operations. These labs analyze hydraulic fluid samples in much the same way as medical labs test blood samples. Just as a blood test helps a doctor diagnose health problems, a sample of hydraulic fluid can help pinpoint sources of contamination and determine whether or not a system has adequate filtration.

Analysis services help reduce catastrophic equipment failures, maintain optimum component performance, and identify any substandard maintenance practices. The result is often increased productivity for the user.

The testing process
The analysis process begins by drawing hydraulic oil or lubrication fluid from a system when it is at normal operating temperature. Lab-equipped manufacturers of hydraulic products generally provide analysis kits with ultra-clean specimen containers, which are to be filled with the fluid flowing out of a system's sampling valve, sump drain, or reservoir drain. All surfaces need to be extremely clean during sampling to avoid contamination, which can affect the accuracy of fluid testing.

Some labs provide two kit styles (for testing with and without spectrographic analysis), allowing for different levels of testing. A user simply places a filled specimen container in the kit's shipping container and mails it to the lab. Users can opt for any method of shipment, since the age of the specimen generally does not affect testing results.

Once at a lab, sophisticated computer programs and laboratory diagnostic equipment are used to test hydraulic or lubrication system fluid samples that are drawn from the user's equipment. Testing may include:

  • photomicrography — detects fluid contaminants, including size and type.
  • viscosity (ASTM D445) — measures fluid flow rate. Too high or too low a viscosity may lead to fluid breakdown, inefficient equipment operation, premature system failure, or damage to other components.
  • water (ASTM E203) — determines water content in a fluid. Excess water reduces the viscosity of hydraulic fluid, which can increase the likelihood of adverse chemical reactions and degrade equipment performance.
  • Drawdown Particle Isolation — detects insoluble contaminants in fluids, including insoluble particles and organic or inorganic gel-like matter.
  • Automatic Particle Count (ISO 11500) — counts the number and size of particles in a fluid sample and then defines contaminants according to size distribution and quantities. Results indicate any needed corrective actions.
  • Spectrometric Analysis (ASTM D 5185) — evaluates the condition of additives in a fluid, as well as wear metal content.
  • Energy Dispersive X-ray Fluorescence (ASTM E 1508) — pinpoints contaminant types, which aids in identifying origins.
  • pH (ASTM E 70) — determines the acidity or alkalinity of watercontaining hydraulic fluids.
  • Total Acid Number (ASTM D 974) — measures the amount of acid and acid-acting material constituents in a fluid. An increase in TAN indicates oxidation or acid contamination.

Once testing is complete, users are provided with the findings, which may include photos of the contaminants and tips on how to improve or maintain current fluid conditions. Conducting trend analysis, by comparing data from two previous samples, with current results, may also be meaningful.