Hydraulic Troubleshooting: The Basics

The Hydraulic Troubleshooting HandbookOne of our members wrote to me regarding the following problem:

“We have a hydraulic system that operates two cylinders. The maintenance staff recently reported that the pump (piston-type) had failed – for reasons unknown at this time. The tank, valves and cylinders were cleaned and a replacement pump installed. The new pump is delivering a maximum pressure of 1,000 PSI and appears to be creating heat. Can you suggest some tips to find a solution to this problem?”

In any troubleshooting situation, no matter how simple or complex the hydraulic system, always start with the basics. This ensures that the obvious is never overlooked. In order for the ‘obvious’ to be obvious, the fundamental laws of hydraulics must be kept in mind:

–Hydraulic pumps create flow – not pressure.
–Resistance to flow creates pressure.
–Flow determines actuator speed.
–Pressure determines actuator force.
–Fluid under pressure takes the path of least resistance.
–When a fluid (liquid) moves from an area of high pressure to an area of low pressure (pressure drop) without performing useful work, heat is generated.

Theory is great, but it always makes more sense when put into practice. So let’s apply these fundamentals to the above situation in a way that ensures the obvious things are not overlooked.

“The new pump is delivering a maximum pressure of 1,000 PSI…”

We know that a hydraulic pump can only produce flow (pressure is created by resistance to flow). It follows that if the pump can’t get oil it can’t produce flow. So check that the reservoir is filled to the correct level, the breather is not clogged, the suction strainer or filter (if fitted) is not clogged, the pump intake isolation valve is fully open and the pump intake line is otherwise unrestricted.

If the pump is producing flow, then an absence of pressure indicates an absence of resistance to flow. Knowing this, and that fluid under pressure always takes the path of least resistance, the task now is to find the point at which pump flow is escaping from the circuit. If you’re skilled in reading and interpreting hydraulic symbols, the system’s schematic diagram (if available) can be useful in identifying possible locations.

“The new pump… appears to be creating heat.”

Because heat is generated when there is a pressure drop without useful work, using an infrared thermometer to check the temperature of individual components will quickly lead us to the hottest part of the system – and the probable location of the internal leakage. Note that in a properly functioning system fitted with a piston pump, it is not unusual for the pump case to be the hottest part of the circuit. These checks should have taken less than 10 minutes. If nothing conclusive was revealed, I would continue the process of elimination using a flow-tester to conduct a direct pump test.

Bottom line: not having a solid understanding of the fundamental laws of hydraulics can result in costly troubleshooting mistakes. And if you do have a hydraulics problem to deal with, you need the Hydraulics Troubleshooting Cheat Sheet.

It shows you how to tackle any hydraulics problem in a way that ensures correct diagnosis in the shortest possible time–even if your knowledge of hydraulic systems is not extensive. And because it’s based on PRINCIPLES, not guesses, this ‘cheat sheet’ will get you out of trouble most of the time.

It’s FREE and available for immediate download here

14 thoughts on “Hydraulic Troubleshooting: The Basics

  1. I have a 2003 Massey Ferguson Model 471 where my hydraulics quit working for my loader and my power steering. The hydraulics work for the PTO and 3-pt. I changed the hydraulic filter but to no avail. The power steering and all hydraulics run off the same hydraulic fluid. Any other suggestions on what I should try next?

    • Hi Micheal, suggest you get my Hydraulic Troubleshooting App for your smart phone and work through the steps in that. The App can be downloaded free from the Google Play Store for Android and the Apple App Store for iphone.

  2. mf 35 hydraulics quit working. went in to pump and it don’t seem to be pumping oil to piston on top. does it need rebuilt or could something else be wrong. took filter out cleaned and put back.

    • Bart, as a starting point, download my Hydraulic Troubleshooting App. It’s free and it’s available now from Google’s Play Store and Apple’s App Store.

  3. I just changed a cylinder on my hoist and then lowerd the unit . Sounded like the air from that cylinder and in the lines went back into the hydrolic power pack . But now i try to relift my hoist and it sounds like its working but it wont go up . Is it possible i blew my pump because i se that oil can cerculate threw the lines but it wont build pressure .
    Is it possible that pump has to be primed . Can someone help me

    • Nolan, as a starting point, you should download my Hydraulic Troubleshooting App. It’s free and it’s available now from Google’s Play Store and Apple’s App Store.

  4. my ferguson t-30 wont pick rear buckit up with more than about 150 lbs I did change fluid at first it seemed to work smooth now after a couple of months not so good fluid was milky before changing I flushed system with diesel fuel and drained well fluid is milky again should I change it again

    • George, milky color is a sign of water getting in — you need to find and stop the source of water ingression. Also, flushing with diesel is no the best idea, if you don’t get it all out it will dilute the viscosity of the hydraulic oil. For more help with hydraulic troubleshooting get my free phone app The Hydraulic Troubleshooting App and/or The Hydraulic Troubleshooting Handbook:

    • Larry, that is unusual. If the engine radiator incorporates an oil cooler and there is a crack between the two that could explain it. Otherwise you’d have to consider accidental or intentional top-off with hydraulic oil.

  5. I have a 2 yr old dump trailer. Today I lifted it up to dump firewood. No problem until I let it down. About 2 feet from being all the way down to the frame it stopped making noise but continued to close at a slow rate. Right before it completely closed the cap blew off the hydraulic plastic reservoir and hydraulic fluid shot several feet up in the air- I let it cool down and tried it about 2 hrs later and it worked perfectly. I have yet to add about 2” of fluid blown out. What caused this?

    • Bob, sounds like aeration/cavitation of the oil. This can be caused by air ingression and/or restriction at the pump inlet.

  6. Case 85xt rt. Drive has no movement,stopped working real fast.
    Could a relief valve be bad or the tandem drive pump,or the drive motor? How to tell what is bad? Thanks

    • Clyde, it could be a lot of things including major failure of the hydrostatic transmission, or a minor control issue. A good place to start is by downloading my troubleshooting app from the Google Play store or Apple app store

Leave a Reply

Your email address will not be published. Required fields are marked *