What are the symptoms of bad hydraulic fluid?

The signs of a bad hydraulic fluid are typically in the form of a darkened or milky oil color, a burning or sour odor, slow or unsteady cylinder movement and unusual noises (whining or cavitation) and rising temperatures, the formation of foam in the reservoir, and even visible particles or sludge that are present in the fluid. Any of these indicators warrants a test sample to oil analysis since the continued use of degraded fluid causes wear and tear on valves, pumps and seals, and could cause catastrophic failure of the component.

What is the significance of hydraulic fluid condition?

Hydraulic fluid is more than simply transferring power. It also lubricates internal components. removes heat, seals clearances in valves and pumps, and prevents corrosion. If the fluid is degraded due to corrosion, oxidation, or additive depletion, it ceases to perform these functions correctly. This results in an engine that is hotter and more prone to wear and ultimately fail by a variety of ways. The consequences are more costly than a simple fluid change could have been.

Finding the problem earlier is usually cheaper than replacing a pump cylinder. The majority of hydraulic problems attributed due to "bad luck" or "component defects" can be traced to a fluid that was allowed to degrade long past the point that warning signs could be observed.

Visual symptoms that you can test without the use of any tools.

Color change

Fresh hydraulic fluid is usually transparent amber or a light golden. As it gets older as it ages, the process of oxidation gradually darkens it towards black or brown. An easy way to test this is to test the blotter to place a small amount of the fluid on a white filter paper and then compare the pattern of spreads and colors against a new sample. The darkening of the color is usually a sign of an overheated or oxidation process or oxidation-related byproducts growing up more quickly than the additive package in the fluid could neutralize the oxidation byproducts.

Cloudy or milky in appearance

A look that is hazy or milky usually indicates water damage. Water can get into the system through damaged seals, condensation within the reservoir or through a damaged heat exchanger. Even tiny quantities of water, as low as 0.1 percent -- could accelerate oxidation, lead to depletion of additives, and cause corrosion on metal surfaces within the internal. Milky fluid shouldn't be ignored as water contamination can quickly increase after it has begun.

Sludge or varnish or visible particles

Sludge accumulation into the reservoir as well as a slick varnish layer on valve spools or cylinder rods is a sign of advanced oxidation and inadequate filtering. Varnish is especially problematic because it causes valves to cling or move slowly, long before the liquid appears "dirty" to the naked eye.

The smell-related symptoms

A sour or burnt odor is among the most reliable indicators of thermal degrading. Fluids that have been repeatedly heated produces a distinct burning or scorched smell, that is caused by the breakdown of base oil and the additives. If the smell of the fluid is distinct in comparison to a fresh specimen It's a clear indication that the operating temperature has exceeded the limits of thermal stability at some point during its life span.

Performance indicators in the system

The cylinder's movement is slow or inconsistent.

The degraded fluid loses control of viscosity which means it is unable to longer hold the strength of film necessary for smooth, reliable actuator movement. Cylinders might expand or retract faster than usual, pause in mid-stroke, or react erratically in response to commands from valves. It is usually mistaken for the problem with a valve or cylinder however the fluid itself could be the reason.

Operating temperature increase

Fluid that has lost the ability to efficiently disperse heatbecause of additive depletion or oxidation byproducts contamination results in the entire system to become hotter to run. If temperatures in the return line or reservoir are trending up without variation in the rate of duty or the ambient temperature, the fluid state should be one of the first items to be checked.

Pump noises: whining, cavitation or knocking

A strange sounding pump is an important symptom that should not be ignored. A knocking sound or whining is usually a sign of cavitation. It may be the result of fluid that is excessively fluid and viscous (common in cold start that have degraded liquid) or the entrainment of air due to foaming fluid. Cavitation that is prolonged can damage the pump's internals quickly, and is one of the most efficient routes to complete pump replacement.

The reservoir is awash with foam.

Foam that is excessively deposited on top of the the reservoir is usually a sign of the entrainment of air, water contamination or depleted antifoam additive package. Foam can hinder the fluid's ability to transmit force and lubricate effectively, and also causes oxidation to increase because more air is interacting to the oil.

Contamination-specific symptoms

Particulate contamination

Metallic particles found in the fluidusually visible as magnetic residue if you check it by using a drain-plug magnet -- can indicate a problem with wear and tear in the valves, pumps, or cylinders. This is not the same as damage to the fluid, but is usually a consequence of running degraded fluid for too long, as the loss of lubricating films increases the rate of contact between metal and metal.

Additive depletion

There are some symptoms that don't appear visually. Anti-wear, anti-oxidant and anti-foam additives diminish gradually as they are used, and a fluid may appear as clean, yet have lost the majority of its additives that protect it. This is the reason why visual inspection alone isn't enough for systems that are critical regular analysis of oil is the only method that can identify the presence of depleting additives prior to it causing damage.

How do you confirm a suspicion of an issue?

The smell and visual tests can be useful for screening first however, they don't provide a precise measurement of the state of the oil. An accurate oil analysis usually examines:

• Viscosity is a an inversion of the liquid's viscosity grade
• The content of water is expressed in parts of a million
• Particle count is determined in relation to ISO 4406 cleanliness codes
• "TAN" (Total Acid Number) A rising TAN can indicate an increase in oxidation
• Levels of additives -Anti-oxidant and antiwear reserves

The sending of a sample to an lab or using an on-site portable analyzer when the first indication of any symptom mentioned above will provide a scientific basis to decide whether to treat, filter or replace the fluid completely.

The prevention of fluid degradation in the beginning

• Control operating temperature Maintain the system within the temperature range of the fluid; set up or keep heat exchangers when necessary.
• Maintain proper filtration Check the micron ratings of filters to requirements for cleanliness of the system and replace filters as needed and not just when the bypass indicator goes off.
• Guard against water intrusionUse breather filters that are rated to keep moisture out and check seals on a regular basis.
• Use a regular schedule for analysis of fluids Regular sampling can detect the early oxidation and depletion of additives before any visible signs appear.
• Keep fluid in a safe place even the fluid that's in drums can degrade faster if exposed to extreme temperatures or moisture prior to being used.

How often do you test hydraulic fluid for degradation?

A majority of industrial equipments benefit from an oil test every 500 to 1,000 hours of operation for high-temperature or high-duty cycles, but high-duty cycle systems might require periodic testing of 250 hours or more. Mobile equipment manufacturers typically stipulate intervals in their maintenance manuals according to the severity of the application.

Does a faulty hydraulic fluid cause damage to seals, even though the system continues to function normal?

Yes. Oxidized fluid gets more acidic as time goes by and this acidity may cause damage to seals gradually and cause swelling, hardening or cracking before performance indicators are apparent.

Is dark hydraulic fluid always a sign that it is time to be replaced?

It's not always. Some formulations of fluids get darker naturally as they age, with no loss of performance. Color can be a helpful screening indicator, however it must be verified through an oil analysis instead of being the only basis for a change.

What's the difference between contamination and degrading?

Contamination refers to foreign matter that enters the fluid, like dirt, water and metal particles. Degradation refers to the fluid's chemical breakdown due to the process of oxidation, thermal stress as well as additive depletion. These two processes are frequently occurring in tandem as contamination speeds up degradation.

Does flushing the system repair damaged hydraulic fluid?

A complete system flush coupled with a change of fluid will stop the degradation process, however flushing on its own won't solve the issue when the root causelike excessive heat or continuous water intrusion isn't addressed. This is because this new liquid will break down in the same way like the old one did.