What happens if hydraulic oil is contaminated?

Hydraulic systems are among the largely unnoticed powerhouses of modern industry. They power excavators that tear around construction zones, raise aircraft landing gears up to 3000 feet, press automobile panels into the shape of factory floors, and keep agricultural machinery in operation throughout the harvest season. At the heart of each of the systems lies a basic substance called hydraulic oil. However, when the oil gets polluted, the effects radiate outward in ways that can be costly, hazardous, and, often, completely preventable.

Let's look at the effects of contamination on hydraulic oil and, in turn, on the equipment that relies on it.

What is the definition of hydraulic oil contamination?

The contamination of hydraulic oil occurs when foreign matter enters the hydraulic fluid, causing changes to its chemical or physical properties. Contaminants are broadly classified into three categories:

Particulate contamination can be caused by solid particles, such as metal shavings that are derived from worn components, dirt, dust, rubber fragments from seals, weld spatter that is left in a new system, or dust that is absorbed by the seal of a reservoir that is not properly sealed. They are the most prevalent form and are arguably one of the worst.

The water contamination occurs when water gets into the system via condensation within the reservoir, leaks in a cooler, exposure to rain on machinery outside, or even excessive humidity in the environment around it.

Chemical contamination can be caused by improper fluids that are mixed (such as mixing with the wrong grade of viscosity or mixing different types of oils); degradation byproducts resulting from the process of oxidation; as well as incompatible additive packages that react with one another.

In reality, a contaminated system usually has several types at once, and the consequences can be compounded.

The damage cascade

1. Wear and tear of components accelerates

Hydraulic pumps, valves, actuators, and cylinders are precisely engineered to extremely tight tolerances, often determined in microns. When particles move throughout this system, they behave like sandpaper over these surfaces. Small particles as tiny in size as 10 millimeters (invisible for the uninitiated) can scratch the valve spools, cut bores on cylinders, and degrade valve vanes.

The wear accelerates itself: wear causes contamination, and wear creates metal particles, which in turn cause more contamination. Engineers refer to this as "wear debris generation," and it's among the most dangerous cycles in mechanical maintenance. If left unchecked, what began as a tiny snare of dirt can degrade the hydraulic pump that costs thousands of dollars in just a few months.

2. Valve failure and stuck

Proportional valves and servo valves are the most susceptible. These valves regulate the exact circulation and the pressure in hydraulic fluid and rely on small clearances in order to function. Even a tiny accumulation of particles could cause a valve's spool to slow down or become stuck and cause an unsteady actuator and loss of precision in position and, in the worst-case scenario, an inoperable valve when it is in an open or closed position.

In the world of industrial automation, a valve that is stuck does more than slow down production—it could also cause unsafe, uncontrolled machine movements.

3. Cavitation

The presence of water, even in tiny amounts, reduces the temperature of hydraulic fluid. At low pressure at the inlet of the pump, the water dissolved in it can evaporate, creating bubbles of vapor. If those bubbles move into higher pressure zones and then collapse in a flurry, they collapse with tremendous force—a process called "cavitation."

Cavitation can cause pitting on metallic surfaces, which resembles moonscapes under the microscope. It creates noise (a distinct sound of rattling generated by the pump) that causes vibration. It decreases the efficiency of flow and quickly destroys the pump's internal components. A pump that is suffering from cavitation may fail within the smallest amount of time it is expected to live.

4. Degradation of fluids and oxidation

Heat is the antagonist of hydraulic oils, and contamination only makes the relationship even more tense. Water is the primary factor that accelerates the degrading of the oxidative properties of base oil, which causes it to degrade an additive's package that is a meticulously well-balanced blend of anti-wear agents such as oxidation inhibitors and corrosion preventatives and viscosity enhancers that make the oil more than an ordinary fluid.

As the additive package is depleted, it loses its ability to shield metal surfaces, causing the formation of rust and the accumulation of varnish on valve surfaces, as well as the buildup of sludge in filters and coolers. The oil essentially ages rapidly, changing from a transparent amber color to a murky dark brown fluid that has a burning scent.

5. The degradation of hose and seal

Chemical contamination, especially incompatible fluids and aggressive oxidation byproducts, can damage the elastomers in hoses and seals. Seals can expand and shrink, harden, or break depending on the kind of contamination. A damaged seal can lead to leaks from the outside, which can cause risks to safety as well as environmental dangers as well as internal leakage through actuators, which reduces effectiveness and control.

6. System overheating

A system that is contaminated is a system that's inefficient. Degraded or worn-out components create internal leakage, which creates heat, instead of doing efficient work. Filters that are blocked push more fluid through bypass valves, which reduces the efficiency of cooling. This results in a hydraulic system operating with more heat than it should, and the increased temperature can accelerate all other types of degradation that have been discussed before, which creates another damaging feedback loop.

The real-world implications

The effects that follow from pollution by hydraulic oil aren't just technical; they're also financial and operational.

The most unplanned downtime is the one that takes the first and most severe affliction. A malfunctioning hydraulic system on an excavator could cause a construction site to be buried for days while the parts are procured and fitted. In manufacturing environments with high throughput even a minute of downtime can be tens of thousands of dollars.

A shorter component's life significantly raises capital expenses. Motors, hydraulic pumps, and cylinders are costly replacements that occur several years prior to their designed time, an expensive and manageable expense.

Risks to safety are the biggest issue. Hydraulic systems work at high pressures, usually between 200 and 350 bar and occasionally much more. A hose or seal rupture in these conditions can be an extremely dangerous risk to injury. In mobile machines like forklifts or cranes, a failure of the hydraulic system in mid-operation could be fatal.

Environmental liability from spills and leaks is an additional level of risk, especially when it comes to operations that are located close to water sources or regions with strict environmental regulations.

Prevention: The only sustainable strategy

The positive side is that the problem with hydraulics can be avoided by implementing disciplined maintenance procedures.

The filter is the first step in defending. Properly rated filters—pressure line and return line, with suitable micron ratings to the system—should be replaced and maintained on a regular basis. Utilizing a filter that's too fine for the components of your system will cost you money.

Breather filters on reservoirs deserve special attention. When the fluid level decreases and air is drawn in, the air transports water and particles. A high-quality desiccant breather will eliminate this issue completely.

Analysis and sampling of fluids is, in fact, the most effective maintenance tool. Sending a small amount of oil to a lab for analysis of the count of particles and viscosity, water content, and additive analysis provides the user an earlier warning mechanism that will identify contamination problems early enough to prevent failure. Most equipment manufacturers suggest quarterly sampling intervals.

The proper flushing of newly repaired systems eliminates manufacturing waste, welding spatter, and assembly contamination prior to it being put into service. It's a procedure that is often skipped or missed due to pressure from schedules, resulting in cost-intensive results in the future.

Discipline for handling and storage—with sealed containers Cleaning transfer equipment and clearly labeling the types of fluids will stop chemical contaminants in the systems prior to it even being put into operation.

Hydraulic oil isn't just an item to be used for consumption; it's an essential component of the system. Making it a priority to treat it that way, by keeping track of its condition; ensuring the filtration and sealing mechanisms that protect it; as well as reacting quickly to warning signals, can make the distinction between a hydraulic system that has a full lifespan and one that is unable to meet its needs in a timely manner and with a high cost.

Contamination doesn't signal itself by alarms or warning lights. It is quietly working in a quiet, small-scale manner and molecule by molecule until the damage is accomplished. The machinery and the operations that last for decades are those that recognized the simple truth and developed their maintenance processes around it.