What is in this article?:
- Hydraulic fluid contamination testing
- New technology enhances assessment
Methods of assessing fluid cleanliness have become more sophisticated and effective, but also easier and more convenient to use. Here's a summary of what's happening.
New technology enhances assessment
Whether your car has an "idiot light" or a real temperature gauge, its designers deemed the engine's water temperature important enough to monitor it continuously. After all, it wouldn't do much good to have your engine's water temperature checked only when you stop for gas. It's much more likely that a problem would occur while you were on the road rather than when you were at the gas station.
Monitoring contamination of hydraulic fluid would at first seem to be much less critical than engine water temperature. After all, fluid usually becomes contaminated gradually, so monitoring its condition frequently enough can identify problems before they cause any real harm. Engine temperature, however, can increase quickly once a problem occurs. If a hose ruptures, the water pump gives out, or the radiator leaks, the engine can quickly overheat.
Contamination, under certain conditions, can also act quickly to cause catastrophic failure in a hydraulic system. For example, if a pump ingests enough air to cause serious cavitation, it can become inoperative within days. Or if a large quantity of water flows through a system, hydraulic fluid can lose its lubricity, which will result in rapid wear of components. If either of these events occurred a few weeks before a scheduled fluid analysis, the machine could undergo costly downtime.
Granted, these types of problems happen rarely. But if the equipment costs millions of dollars or works in an operation where downtime is measured in thousands of dollars per hour, it becomes practical to continuously monitor fluid cleanliness. It is for cases like these that companies are developing systems to monitor the cleanliness of hydraulic fluid continuously while a system is running.
One such prototype system routes pressurized fluid from the pump into a tube through which light is transmitted. When the fluid is clean and relatively free of air and water, a receptor detects the amount and pattern of light transmitted through the fluid.
As the fluid becomes more contaminated, the amount and diffraction of light transmitted through the tube changes. If undissolved water or air is present, the transmitted light becomes more scattered. Calibrating the receptor to these different conditions provides an instantaneous indication of the fluids condition. Therefore, a potentially catastrophic failure can be averted by taking appropriate action immediately.
Another emerging technology is a system that enables users to go beyond particle counting and actually analyze wear debris. The system consists of hardware to generate digital photomicrographs and software to aid in analyzing the digital images. The hardware includes a digital camera, an adapter to mount the camera to a microscope, and a PC-compatible image-capture card.
Once imported to a PC, images can be compared to those in an atlas of known wear debris using wear debris analysis software. The software also aids in characterizing descriptions, managing data, and generating reports. The analysis can also be incorporated into maintenance and SPC software used for plant operation and quality assessment.
Special fittings help keep samples clean
Tapping into a hydraulic system to sample fluid creates the potential to contaminate not only the fluid in the hydraulic system, but the fluid sample as well. To help prevent either from occurring, test ports designed for fluid sampling should be mounted permanently to the equipment and have protective caps to keep dirt away from the sampling port. The cap is removed only when taking a fluid sample and replaced immediately afterward.
Shown at right is a low-pressure test fitting for sampling fluid from hydraulic return lines without having to shut down equipment. Pressing on the pushbutton opens a check valve that routes fluid from the hydraulic system out through the sampling port. Models for taking samples from high-pressure lines work in a similar fashion, but use a threaded connection instead of a pushbutton to open the check valve.
The test port avoids introducing external contaminants into the fluid extracted from the hydraulic system. However, to ensure accurate samples, tubing leading to the sampling vessel and the sampling vessel itself must be absolutely clean. The tube should be discarded after a sample is drawn and replaced with a new one before each subsequent sampling.
Don't ignore compressed-air cleanliness
Manufacturers of compressed air components often cite wet or dirty air as the cause of problems related to a machine's operation or performance. After all, air is a fluid, and accumulated contaminants tend to restrict or even block flow. And with many of today's pneumatic components requiring increasingly cleaner air, the potential consequences of contamination are becoming more widespread and pronounced.
Therefore, it is more important than ever that pneumatic systems contain air drying equipment and properly rated filters. Furthermore, as with hydraulic fluid, compressed air cleanliness should be assessed periodically to ensure maximum performance and reliability. This task has become easier thanks to portable instruments that can monitor compressed air contamination concentration, pressure dewpoint, air temperature, and pressure.