I don’t even have to ask — I know you’re already datalogging your power unit’s particle counter to track contamination levels, and you’re using the latest wireless pressure transducers and flow meters to track case drain pressure and flow. Perhaps you have another half-dozen metrics that your custom maintenance software automatically tracks, including mean time between failures and machine uptime percentage.
You’re logging your filters’ pressure drops, mapping your major components’ temperatures, and sampling your oil every quarter to track water saturation and total acid number, all the while posting Mean Time Between Failures charts on the Lean Six Sigma whiteboard outside your office. Because, of course you are. Because I know each and every one of you is doing all this and more (Right? RIGHT??), let’s step outside the box and talk about unconventional KPIs you can add to your repertoire that aren’t so pedestrian.
We all know hydraulic power units vibrate, and we all know those vibrations lead to frequently insidious auditory torture. Those vibrations are packets of information ready to be collected and analyzed. By installing high-speed, high-resolution pressure transducers, you can track pressure waves near pumps, motors, and valves to detect anomalies. Despite an even sounding vibration, just like soundwaves, the frequency and amplitude can be measured from 1-20 kHz (or higher). You want to see consistent, dominant amplitude expected from pistons or gears, for example, with no new harmonics possibly caused by cavitation/aeration, metal-on-metal wear, or cylinders chattering.
Valves are expected to shift quickly to provide the responsiveness your actuators require to perform well. Electric coils create a magnetic field to move a metal pin, subsequently shifting the spool. Some manufacturers publish these shift speed curves, which vary based on both flow and pressure differential through the valve. Still, installing pressure sensors at the workports just downstream of the valves allows you to track the baseline data relevant to your application. Over the years, you can monitor shift performance to see if spools are sticking or coils are weakening, giving you the opportunity to repair or swap out valves on the verge of failure.
I’ve mentioned previously that mapping the temperatures of pumps, actuators, reservoirs, and valves provides valuable insight to potentially discover hydraulic energy being lost before doing useful work. However, those recommendations involved laser thermometers or infrared cameras. However, by installing temperature transducers in strategic locations, you can trend fluid bypass over time to predict imminent failures.
Temperature sensors in pump case drain lines, relief valve tank lines, valve manifold return lines, and other strategic locations allow you to track heat, which can be compared to both ambient conditions and previously trended data. An increase in temperature in the relief valve tank lines, for example, points to either an issue causing over-pressurization or with the valve itself. You can go a step further and add temperature sensors to the actuator work lines. If your PLC senses a temperature rise at the cap-side port of your cylinder during retraction, followed by a head-side rise during extension, you should investigate whether your piston seal(s) are leaking and generating heat.
Today’s rise in cheap technology and electronics has given us the resources to collect and process data like never before. Such datalogging of KPIs would have been impossible twenty years ago outside of spaceships and Formula 1 racing cars. You simply have no excuse for avoiding the tracking of KPIs, even unconventional ones.
Filed Under: Components, Engineering Basics, Troubleshooting
