Hydraulic System Testing: Step-by-Step Guide

Regular hydraulic system inspections help keep track of the system’s performance and efficiency. In this guide, we’ll walk through additional tests that go beyond basic visual inspections, such as cylinder drift and travel cycle times. These tests can help you identify potential issues before you can detect efficiency loss yourself.

Check out this video to see the tests in action, and then read on for the instructions.

Prepare for Service

Before testing your Cat^® excavator’s hydraulics, check your Operation and Maintenance Manual (OMM) for proper safety procedures. Also put on appropriate personal protective equipment (PPE).

Move your equipment to a hard, level surface in an open area. You will need plenty of space in every direction, including above, because you’ll need to raise the boom and stick fully during testing.

For most machines, this means 25 to 30 meters (82 to 98 feet) plus the length of your machine in each direction. Depending on your machine’s size, you may need up to 50 meters (164 feet) of open space. Make sure the bucket is empty before you start, and place the hydraulic activation lever in the unlock position.

Testing Materials

You’ll need a timer, tape measure, ladder and the service instructions for your specific machine. If you have a pressure gauge, bring it along, but it’s not essential.

For this example, we’re using a Cat 323 Hydraulic Excavator. Specifications may vary for your equipment, so check with your Cat dealer or refer to SIS 2.0 for service instructions and measurement ranges. If your results are outside the acceptable range, consult a technician for troubleshooting.

Start by increasing the hydraulic oil temperature to 55 degrees Celsius (131 Fahrenheit), plus or minus 5 degrees (9 Fahrenheit).

Cylinder Drift Check

To measure the boom cylinder head end, position the linkage as shown in your service manual. Measure the cylinder length from pin to pin and record the number. You may need a ladder and a second person to help, depending on your machine size. If you don’t feel safe or don’t have the right equipment, skip this test.

Here’s a practical approach if you're doing this test without help from another person:

Position the linkage correctly.
Stand safely on the ground or a ladder and measure a reachable distance (such as 10 centimeters or inches).
Mark the rod’s chrome at that point.
Shift to neutral, engage the parking brake and turn off the engine.
Wait three minutes, then measure again to see how far the mark has shifted.

For example, if the distance is now 11 cm or 1 inch, that’s a 1 cm or 1 inch drift. Compare the drift to your equipment’s specifications. Repeat this process for the bucket cylinder rod end and the stick cylinder head end, referencing your manual for the correct linkage positions and timing.

Cylinder Cycle Times

Test cylinder cycle times to help identify internal cylinder leaks, main pump flow issues and other system problems. Position the linkage as shown in your service instructions. Make sure your hydraulic temperature is still above 50 degrees Celsius (122 degrees Fahrenheit).

Set the engine speed to maximum (either 7 or 10, depending on your machine).
Turn off automatic engine control, shift to neutral, engage the parking brake and fully retract the bucket.
Time how long it takes to fully extend the bucket at full speed.
Repeat this process to time how long it takes to retract the bucket.

Test the boom cylinder cycle times, making sure you have enough clearance. Then measure the time for both full boom extension and retraction.

Finally, test the stick cylinder extension and retraction times. Be careful not to hit the ground with the lift arm during testing, as that can be dangerous.

Travel Cycle Times

Travel cycle times check machine speed and final drive motor performance. Use cones or blocks to mark distances:

Place a cone next to the front of your track to mark your starting point.

Measure and place cones 5 meters (16.4 feet) and 25 meters (82 feet) away from your starting point.

With the bucket positioned 1/2 to 1 meter (1.6 to 3.3 feet) off the ground and the hydraulic oil temperature at least 50 degrees Celsius (122 degrees Fahrenheit), set the engine speed to 7 or 10.

Place the travel speed control in high position, then operate forward. Start the timer at the second cone and stop at the final cone.

Repeat the test with the travel speed control in low position, and then do the same test in reverse, starting 5 meters (16.4 feet) in.

If space is limited, you can raise one track and mark a shoe for tracking revolutions. Time how long it takes for three revolutions at both high and low speeds, forward and reverse, for both tracks.

Refer to SIS 2.0 for acceptable speed variations for your equipment.

Pump Main Relief Test

This test measures how much pressure your pumps are delivering. If the pressure is too high, components could get damaged, and if it’s too low, you won’t get optimal performance.

Check the hydraulic oil temperature and set the engine speed dial to 7.

Shut off automatic engine control, ensure power mode is active, and stall out your implements to reach maximum pressure.

Check the pressure values for both pumps on your monitor or gauge. You may need to switch the stalled implement to read the other pump.

Next, check your pilot relief valve and swing cycle time using SIS 2.0 instructions. If any values are outside the acceptable range, work with a technician to troubleshoot.

Diagnostic & Event Codes

To check diagnostic codes:

Turn on your equipment and press the application menu icon.
Select Settings, then Service, and finally Diagnostics.

Here, you’ll find active and logged diagnostic and event codes. If you see an active code, save it to move it to logged codes. Scroll to the bottom to clear out all logged codes.

By performing these tests and inspections regularly, you can ensure your hydraulic system runs efficiently and prevent major issues before they start.

For more support, reach out to your authorized Cat dealer.