Hydraulic Circuit Testing

The Basic Steps of Diagnosis and Testing

1. Know the System

In other words, "Do your homework." Study the machine technical manuals. Know how the system works. Is it open or closed center? What should the valve settings and pump output be?

Keep up with the latest service bulletins. Read them and then file in a handy place. The problem on your latest machine may be in this month's bulletin, giving the cause and remedy. You can be ready for any problem by knowing the system.

2. Ask the Operator

A good reporter gets the full story from a witness- the operator. He can tell you how the machine acted when it started to fail, what was unusual about it. Try to find out if any do-it-yourself service was performed. You may find that the problem is elsewhere, but you should know if any adjustments were tampered with.

3. Operate the machine

Get on the machine and operate it. Warm it up and put it through its paces. Don't completely trust the operator's story - check it for yourself. Are the gauges reading normal? If not, it may be hydraulic trouble or faulty gauges. How is the performance? Is the action slow, erratic, or nil? Do the controls feel solid or "spongy"? Do they seem to be "sticking"? Smell anything? Any signs of smoke? Hear any funny sounds? Where? At what speeds or during what cycles?

4. Inspect the Machine

Now get off the machine and make a visual check. Use your eyes, ears, and nose to spot any signs of trouble. First inspect the oil in the reservoir. How is the oil level? Is the oil foamy? Milky? Does it smell scorched? Does it appear to be too thin or too thick? How dirty is it? If the oil is very dirty, also check the filters for clogging.
Feel the reservoir and lines. Are they hotter than normal? Are they caked with dirt and mud? Is the paint peeled off from heat? Check the pump inlet line for restrictions. Check for collapsed hoses. Follow the circuit and keep on checking. Look for oil leaks at line connectors. Watch for air leaks at loose clamps, etc.

Check the oil cooler, is it free of trash and mud? Look closely at the components. Inspect for cracked welds hairline cracks, loose tie bolts, or damaged linkages. While you inspect, make a note of all the trouble signs.

5. List the Possible Causes

Now you are ready to make a list of the possible causes. What were the signs you found while inspecting the machine? And what is the most likely cause? Are there other possibilities? Remember that one failure often leads to another.

6. Reach a Conclusion

Look over your list of possible causes and decide which are most likely and which are easiest to verify. Use the Troubleshooting Charts at the end of this section as a guide. Reach your decision on the leading caused and plan to check them first.

7. Test Your Conclusion

Now for the final step: before you start repairing the system, test your conclusions to see if they are correct. Some of the items on your list can be verified without further testing. Analyze the information you already have.

Were all the hydraulic functions bad? Then probably the failure is in a component that is common to all parts of the system. Examples: pump, filters, system relief valves.
Was only one circuit bad? Then you can eliminate the system components and concentrate on the parts of that one circuit.

Testing the Machine

Now your list is beginning to narrow so that you can point your tests at one or two components. The next part of this chapter will tell you how to test the system and pinpoint these final troubles.