The sludge effect

Preventing harmful sludge buildup by picking the right hydraulic fluid can help you win the race against equipment downtime.

Imagine running a marathon every day — almost indefinitely — while your coach, right behind you, demands more speed and quicker times. If we were faced with this challenge, we would certainly rely on energy drinks and other performance fluids to keep our body hydrated, purge toxins from organs, and help keep our joints lubricated.

Oxidation Test ASTM D943M
Results from Oxidation Test ASTM D943M show significantly lower sludge formation of Hydrex AW 46 fluid — even after longer test periods.

Today’s hydraulic equipment has similar needs. Heavy-duty hydraulic systems that operate in industrial plants and outdoor mobile equipment endure some of the toughest operating conditions, running at higher pressures and at increasing higher speeds. In addition, the trend towards smaller reservoirs places more stress on equipment and increases operating temperatures in hydraulic systems.

A system with a smaller reservoir does not allow air and heat to escape as easily, water may not separate as effectively, and contaminants may accumulate faster. The rate of oxidation increases, as does the risk of harmful sludge buildup. Even with a good filtration system, excessive sludge can plug filters, increase equipment wear, and damage the hydraulic pump. In addition, sludge creates a high potential for the formation of varnish, which starts off as a resinous substance, then forms hard deposits on components — especially when in combination with high oil temperatures. As the equipment runs harder, the lubricant may break down faster, risking total system failure and costly equipment downtime.

Hydraulic fluids aren’t always specified with enough attention to detail, but understanding what is expected of them clearly demonstrates the need to consider them a key element in system performance, reliability, and longevity — one that combats harmful sludge buildup and maximizes equipment uptime. Highperformance hydraulic fluid are intended to boost equipment productivity while saving you money. So how do you pick the right one?

Look at oxidation
Starting with a base oil free of impurities is a good first move. Checking the purity of the base oil provides insight into its resilience — resistance to breakdown from oxidation for long life. The purer the base stock, the more it retains its fresh oil properties and the longer it is likely to perform.

Oxidation tests are another tool that can be used to identify a highperformance hydraulic fluid. Not all hydraulic fluids are created equal. When choosing a hydraulic fluid, look at tests that indicate a hydraulic fluid’s ability to resist sludge formation, even after extended hours of operation. An example of an optimal high-performance hydraulic fluid that meets these conditions is Petro- Canada’s Hydrex AW 46. It exhibits high oxidation resistance and minimizes sludge buildup, thus providing longer fluid life. Prolonged fluid life means fewer change outs, less downtime, and higher operating efficiency. As a result, it can save not only time, but money.

Tests indicate sludge levels
Tests have shown that Hydrex AW 46 forms significantly less sludge than other hydraulic oils, even with a longer test period for the Hydrex AW 46. In a standard industry oxidation test — ASTM D943M — 99.5% oxygen flow, 20% water, a temperature of 95ºC, and copper and steel catalysts were used to accelerate oxidation to determine the rate of acid buildup in various hydraulic fluids. After this severe test, the fluids were filtered and sludge samples were examined. The results are shown in the accompanying photos.

In another standard industry oxidation test, ASTM D4310M, Hydrex AW 46 was pitted against a variety of other hydraulic fluids. Hydrex AW 46 formed 200 mg of sludge after 2011 hr, whereas the other fluids formed 500 to more than 1400 mg under the same conditions.

The test conditions mirror those of the first test described. After this test, the sludge samples were weighed. Again, Hydrex AW 46 demonstrated significantly lower sludge formation than other hydraulic fluids.

Formula for success
With hydraulic fluid, you get what you pay for. Sludge can be incredibly damaging to hydraulic components, and using a highperformance hydraulic fluid with high oxidation stability reduces the potential for sludge buildup. This translates to longer lubricant life, resulting in fewer change-outs, decreased equipment wear, and lower maintenance costs. The bottom line is savings in time and money.

Taking measures to ward off the formation of sludge helps ensure the race won’t end before reaching the finish line.

Jennifer Lai is category manager, Hydraulic Fluids at Petro-Canada Lubricants. For more information, call (800) 268-5850, e-mail [email protected], or visit