When troubleshooting, there are two things you should always do before reaching for any diagnostic tools. The first is to check all the ‘easy’ things. And the second is to review any available troubleshooting aids. This includes the hydraulic system’s schematic diagram.
Indeed, the ability to read and interpret a schematic diagram is the hallmark of a competent hydraulics practitioner. It’s also one of the hardest skills to truly master. But mastering this skill will be a lot easier for the next generation of hydraulics pros.
Because no matter what you want to learn these days, there’s an interactive software program available to assist you. For example, several years ago I made a New Year’s resolution to learn how to touch type.
In years long past this would have involved buying a book, enrolling in a course or both. Not these days. You just go down to your nearest office supplies outlet and get yourself a software program called “Mavis Beacon Teaches Typing”. You then spend 20 minutes a day on it, until you achieve the typing speed you need.
The hydraulics equivalent to “Mavis Beacon Teaches Typing” is “Learn How to Read and Analyze Schematics in the 21st Century”, a.k.a. simulation software. And while I could write several pages about the power of simulation software as both a learning and an analytical tool, this is best illustrated with an example.
The molding-press hydraulic circuit shown in figure 1 has a problem. The press cylinder’s rod seal keeps failing-every two to three weeks on average. So the troubleshooting task then is to analyze the circuit and figure out what is causing the recurring rod-seal failure.
To troubleshoot effectively, a reliable PROCESS is required. And the application of good troubleshooting process is the primary focus of this handbook. In fact, as demonstrated in many of the examples throughout, a reliable troubleshooting process will lead to a resolution, even when specific system or component-level knowledge is lacking. And understanding this fact makes you a better troubleshooter right out of the gate.
That said, relevant system knowledge is generally an asset when troubleshooting. And as the following example shows, simulation software is a very efficient way to get it. Let’s assume a young technician on staff has been tasked with resolving this problem. The good news for him is, what he lacks in hydraulics knowledge is at least partially offset by his computer savvy.
He re-creates the circuit in his simulation software. And when he simulates cylinder extension, with a state diagram installed to record pressure on both sides of the press cylinder, what he sees is shown in figure 2.
The cause of the problem is immediately obvious. When the directional control valve is shifted to extend the cylinder, pressure on the rod side of the cylinder (red line on the state diagram) spikes to ~5900 PSI, at which point the pilot-operated check valve opens allowing the cylinder to extend.
Now while this simulation result doesn’t fully explain the fact that the magnitude of this pressure spike is influenced by load-induced pressure, cylinder area ratio and check-valve area ratio, the significance of the latter is fairly obvious from the state diagram (spike pressure on the piston side of the cylinder, shown in blue, is about ¼ of rod-side pressure).
It also happens that the area ratio of the pilot-operated check valve is the easiest thing to change in the circuit (and even easier in the simulation software). So this is what our computer savvy troubleshooter does–see figure 3.
With the area ratio of the pilot-operated check valve changed from 4:1 (figure 2) to 8:1 (figure 3) the spike pressure on the rode-side of the cylinder, prior to the piloted-operated check valve opening, has been reduced to ~1700 PSI–a much more acceptable figure which is unlikely to result in failure of the rod seal.
Problem solved. And without breaking sweat. Of course, our budding troubleshooting hotshot still needs to refer to the relevant texts for a more complete understanding of this issue. But at least he now knows exactly where to look. And this makes his knowledge acquisition process a lot more efficient than the head scratching many of us old timers had to go through!