By Josh Cosford, CFPHS
The Fluid Power House (Cambridge) Inc.
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| Josh Cosford, CFPHS, The Fluid Power House (Cambridge) Inc. |
If you’re reading this, chances are better than a BINGO win that you’re somehow involved with hydraulic equipment on one level or another. Personally, I know hundreds of persons who are in some way related to the operation or maintenance of hydraulic systems, but can count on my toes the number of those persons who have mastered troubleshooting.
We in the industry often ask why there is a deficit of hydraulic masters when the demand is so high for these individuals. Unfortunately, when you visit a guidance counselor in high school, you’re never encouraged to steer your technical career towards a fluid power specialty, because the educational system isn’t in place to produce many top-notch professionals.
This month’s article isn’t intended to be a whining session, but rather some tips on how you can master the black art of hydraulic troubleshooting. When it comes to understanding the physics of fluids, some people just “get it.” Others require some tender loving care. However, a strong background in applied physics and math will give you a head start and help you grasp the concepts quickly.
I’m not saying you need to do differential calculus to medicate hydraulic headaches, but if you understand some of the basic principles like the Law of Conservation of Energy or Newton’s Laws of Physics, you can apply them when solving problems. Combine that with some simple equations, like horsepower calculations or the formula to calculate heat wasted in a hydraulic system, and you’ll be half way to troubleshooting stardom.
Probably the single most important tool in the mental chest of diagnostics is the understanding of the relationship between pressure and flow though a hydraulic circuit. Most importantly, the focus should be on this sentence: Hydraulic fluid takes the path of least resistance.
Think of any hydraulic failure you’ve ever come across. More than likely, some part of the machine wasn’t moving as it should, so a motor stopped turning, a cylinder wouldn’t build tonnage or the entire contraption was overheating. Without knowing anything about those machines, I can tell you that most of those failures involved fluid taking the path of least resistance.
Cylinder won’t clamp? Piston seals were shot, bypassing fluid past the piston instead of creating pressure!
Hydraulic motor stalled? Relief valve is stuck open, dumping pump flow back to tank!
Synchronized cylinders won’t synch? Broken spring in the spool flow divider is causing fluid to go to only one of the cylinders!
The preceding examples are all those representing examples of fluid taking the path of least resistance. When the machine isn’t behaving, remind yourself that the fluid must be going somewhere, so you’ll have to discover where it’s going.
Another one of the top tricks in hydraulic troubleshooting is to know that when pumped fluid is not used to do useful work it is wasted as heat. The amount of wasted heat is usually expressed in BTU/hour, kilowatts or horsepower, which are all interchangeable units of power. For example, if your pump is creating 10 gpm and it’s trying to move a stalled cylinder, then all that flow would be going over a relief valve. If the relief valve setting is 3000 psi, then you’d have 17.5 hp of energy wasted as pure heat (gpm X psi /1714 = hp).
Knowing heat is the result of wasted hydraulic energy can help you find localized heat in the system, which can help you diagnose a failure. By using laser thermometers or infrared cameras, one can spot the source of heat to discover where the stuck, leaking or bypassing components are.
The last tip I want to write about is one that seems almost too simple to mention. Pump flow dictates how fast everything works, and pressure dictates how much force they work with. Although it is more complex than this, I won’t get into those complexities today. However, if your system is sluggish, turning up the pressure won’t make it faster (with exceptions). Also, if you want your cylinders to lift more mass, installing a larger pump won’t create more pressure.
Next time you have a hydraulic failure, think about these three concepts and you’ll be surprised by how quickly you can discover the cause. Sprinkle in years of experience, and you’ll be a troubleshooting guru in, well…years!
Josh Cosford is a certified fluid power hydraulic specialist with The Fluid Power House (Cambridge) Inc. Contact him at joshc@fluidpowerhouse.com or call (519)-624-7109.