How much water is too much?
A common misconception being propagated in the field is that some fluids can handle high amounts of water before reacting. This implies it is acceptable to leave high amounts of water in a hydraulic system. Simply because a fluid claims a high level of stability when water is introduced does not indicate that the hydraulic system will function well with that amount of water ingression. The amount of water content required before a high-quality saturated synthetic fluid will begin to react is so significant that it is very likely that the system will begin to suffer problems from the water itself before hydrolysis occurs.
An analogy is the human blood alcohol level. In the state of Texas, the legal limit for blood alcohol content (BAC) is 0.08, meaning 0.08% of a human’s blood, by volume, is alcohol. A 200-lb man with a BAC of 0.04 has consumed two to three drinks, feels relaxed, and has some impairment of concentration but can still legally drive. This parallels the concept of water in a hydraulic system, where a small ingression of water will have minimal impact on the system and is still acceptable, but not ideal.
The ideal scenario is certainly no alcohol in your blood when you are behind the wheel, or in our case, no water in the oil. At 0.08, the driver in our example is now over the legal alcohol limit to drive. Likewise, our hydraulic fluid has now lost some of its lubricity, resulting in scarring, pitting, and corrosion of component internal surfaces.
At 0.20, the man now has a significant amount of alcohol in his system and experiences severe loss of motor skills and consciousness. Merely because the blood itself can handle significant saturation of alcohol does not necessarily indicate that the body can tolerate it, and the body will eventually shut down.
Our hydraulic system is not unlike the man in our example. The components in a hydraulic system are designed to run optimally using oil, not water. Excessive water in a hydraulic system can and will lead to major cavitation, corrosion, and catastrophic failure of the system.
According to the manufacturers of hydraulic components, what are the recommended standards for water content? Sauer Danfoss’ published literature states, “…the water content for continuous operation must not exceed 0.10% (1000 mg/kg). The lower the better. In principle water is a harmful contaminant, reducing the life of the hydraulic fluid and the mechanical components.” Bosch-Rexroth agrees, stating “Water in the hydraulic fluid may result in wear or direct failure of hydraulic components…During operation, the water content in all hydraulic fluids…must constantly be kept below 0.10% (1000 ppm).” Eaton’s Hydraulics Group also encourages its users to keep their systems free of significant water ingression. “It is recommended that for optimal life of components, water content in a hydraulic system should not exceed 0.07% (700 ppm). Beyond this water content, it can be expected the life of components and fluids will be reduced,” says Thelma Marougy, of Eaton Hydraulics.
The amount of saturation a hydraulic fluid can handle varies dependent upon the base fluid used and the temperature. The percentages above were established because problems related to excessive water — such as microbial growth, pressure rise, and swelling of filters — are often seen as starting at these concentrations.
Putting your fluids to the test
The most common tests for the life of a fluid are the RPVOT (ASTM D2272 — Rotating Pressure Vessel Oxidation Test), the Cincinnati Milacron Test (ASTM D2070) or TOST (ASTM D943). In these tests, fluids are subjected to the worst conditions possible to force them to oxidize. The tests monitor fluids for losses in oxidation resistance and increases in acid levels, as seen in Figure 2.
The TAN, or total acid number, is a common test that indicates the amount of deterioration of a hydraulic fluid. A high or increasing TAN indicates that the fluid is oxidizing — hydrolysis is taking place. Monitoring the TAN in a hydraulic system can provide an early indication of a potential problem and allow preventive maintenance to be conducted on the system as needed, saving both time and money.
In terms of standard mineral oil, an increase in TAN is always a bad thing. However, this is not always true with synthetic ester fluids. Synthetic lubricants can have acidic components that lead to corrosion, but some acids can act as corrosion inhibitors. The TAN for mineral oil based fluids should not exceed 2 mgKOH/g, but the TAN for saturated synthetic alternatives may reach 5 mgKOH/g without leading to any problems. These values will vary and should be verified with the fluid’s manufacturer.
Providing a solution
Panolin HLP Synth is a fully synthetic, high-performance, readily biodegradable, non-toxic hydraulic fluid made from saturated esters. It is combined with high-grade additives, is zinc-free and is environmentally friendly. It leaves no sheen when spilled on water, but appears as visible light foam for easy cleanup. It can resist oxidation at high temperatures and pressures, and prevents gumming and deposits in a hydraulic system. Panolin does not affect conventional sealing materials and provides high corrosion resistance and wear-protection.
Perhaps the most impressive aspect of Panolin HLP Synth is its lifetime-fill capability. Due to its base composition and saturated nature, Panolin does not break down over time. Thus, this fluid is able to last within a hydraulic system for extremely long periods of time without any oil change requirement, decreasing downtime and maintenance costs. Test documentation shows that some users have been using Panolin in their machines for more than 130,000 hr (that’s operating 24 hr/day per day for nearly 15 years) without changing the fluid, as demonstrated in Figure 3.
Panolin has been used globally for decades in applications ranging from railroads to injection molding machines, and cranes to offshore platforms. Its use is growing in the U.S. as lower maintenance costs and environmental regulations become increasingly important.
Not all fluids are created equal, and it is important to understand the differences when selecting your biofluid.
Contact the author at (713) 680-1951 or email firstname.lastname@example.org.
1Sauer Danfoss. "Hydraulic Fluids & Lubricants: Technical Information." Sauer-Danfoss.com. Sept. 2010. Web. 26 Sept. 2011.
2 Ruch, Martin. "Panolin Atlantis - Panolin HLP Synth." Message to the author. 24 June 2011. E-mail.
3 Bosch Rexroth Group. "Environmentally Acceptable Hydraulic Fluids." BoschRexroth.com. Web. 26 Sept. 2011.