For any fluid power system to function effectively, the liquid in the reservoir must be clean and free of contaminants. Hydraulic machinery is extremely sensitive to the presence of foreign elements, including dirt particles, flakes of rust, and moisture. The more particles that enter the hydraulic fluid, the less efficiently the system will operate. Contamination can also lead to overheating and may eventually cause expensive breakdowns and loss of productivity.
To keep your machinery in good working order and avoid the added costs associated with replacing your hydraulic fluid excessively, you should familiarize yourself with the industry standard ISO cleanliness codes. In the following blog post, we’ll discuss how to measure contamination in your system and interpret it using these codes, so that you can maintain optimal performance and prevent component damage.
Is My Fluid Power System Contaminated?
There are multiple ways that contaminants can be introduced to a hydraulic system. The materials used to create seals can become compromised, whether due to direct damage or gradual wear and tear, allowing particles of dirt and rust to slip through. Even if the seals are perfect, however, contamination will eventually occur, as tiny particles flake off the rubber and metal elements during the normal operation of the machinery. Additionally, contaminants can enter externally through breather vents or leaks, or during maintenance if proper procedures are not followed. Over time, these contaminants will build up, hampering the equipment’s ability to perform its job effectively.
To prevent or reduce the damage that can occur over time, hydraulic fluid reservoirs are equipped with filtration systems that collect the contaminant particles as they circulate through the system. Over time, these filters become clogged, causing an increased pressure drop that can trigger bypass valves to open, allowing unfiltered fluid and any contaminants to circulate through the system. For this reason, the filters should periodically be changed, and an occasional sample of the hydraulic fluid should be taken to test for contamination.
How to Collect a Sample of Hydraulic Oil
Collecting a sample of hydraulic oil to test for cleanliness is fairly simple, but before you get started, there are a couple of things to keep in mind to ensure you get an accurate reading. First, for safety reasons, the machinery must be completely shut off and allowed to cool down before you attempt any sampling. Don’t skip this step.
Also, make sure the equipment is completely clean before you collect the sample. Dirty tubes and bottles can introduce contaminants of their own that will cause the test to yield inaccurate results.
When you’re ready to gather your sample:
- Attach a clean tube to a test point somewhere on the machinery
- Attach a sample bottle to the tube
- Carefully use a squeeze bulb to draw out the amount of fluid required by your test kit
- Detach the tube from the test point
- Detach the bottle from the tube
- Securely attach a cap to the bottle
Note that where you take the sample from matters. It should not be taken from the tank itself. As no actual flow occurs there, it won’t offer correct information about the inner workings of the system itself. Ideally, samples should be taken from a working line on the machinery, such as the return line, where the fluid flows at the normal pressure and temperature levels it is subjected to during operation.
Testing the Fluid
The first examination you’ll perform when testing your hydraulic oil is visual. Heavily contaminated oil becomes dark and cloudy and may have obvious flecks of debris floating in it. Make note of the color and anything you see floating.
The majority of the most common contaminant particles are extremely small, measurable only in microns, and cannot easily be detected by the naked eye. To determine if this type of contamination is present in your hydraulic fluid, you’ll need a test kit specialized for this purpose. You can also send the sample to an oil analysis lab for professional testing.
There are several kits you can purchase, depending on how much information you want to assess. Advanced testing kits include titrators to measure acidity, alkalinity, and moisture, but these are not strictly necessary in most cases. Most operators will do just fine with patch testing, which can be done with a very basic kit.
To use the patch test method, you will filter your sample through the patch included in the kit. Follow the manufacturer’s instructions to do so. Most test kits use a syringe and a squeeze bulb to pull the liquid through the patch, leaving the contaminants behind. The patch itself is made of a membrane that blocks particles larger than approximately five microns, meaning it will catch the vast majority of contaminants that affect system performance. Particles smaller than this usually require specialized laboratory testing to detect.
Reading ISO Cleanliness Codes
Once the debris has accumulated on the test patch, you can then observe it through a microscope and compare it to a chart to obtain an accurate idea of the particulate content of the oil. You can use this chart to determine the cleanliness by reading the resulting ISO codes.
The International Organization for Standardization (ISO) has provided a reporting standard for fluid systems listed under ISO 4406. These codes are composed of three numbers—for example, 20/16/40— which, in order, indicate the number of particles larger than 4 microns, 6 microns, and 14 microns. When you have determined these numbers, they can be compared to the manufacturing standards of your machinery to ascertain if the cleanliness is within acceptable levels or if the fluid needs to be replaced.
Hydraulic fluid should be tested regularly to determine if contamination is occurring at a normal, predictable interval or if excessive particulate matter has been allowed to enter. If you discover your hydraulic fluid system is degrading more than expected with regular wear and tear, then it’s possible you need to replace your filters, seals, or other elements of your equipment. If you need new parts or fully custom replacement equipment, contact Aberdeen Dynamics. We’ll discuss your needs with you so that your operation can return to optimal productivity.