The swing motor is an indispensable component of a hydraulic excavator. In fact, without a swing motor, an excavator cannot function properly 【excluding the semi-swing homemade excavators built with scrapped light cars around Tianjin more than twenty years ago】.
In other words, as long as the excavator is operating, its swing system must function. Using an excavator to compact a road is unreasonable—because the ground pressure of an excavator is even lower than that of a household motorcycle!
Therefore, testing the performance of the swing motor is of great importance for the operation of excavators.
Typically, swing motor condition is checked because of performance issues. In the evaluation of second-hand machines and in post-repair inspections, a simple on-machine testing method can provide practical value for users.
Strictly speaking, the smaller the swing motor’s starting torque, the better—it indicates low starting resistance and minimal leakage.
Start the engine, preheat the hydraulic system until the temperature reaches 50 ± 5°C. Release the hydraulic lock, increase throttle until the engine runs at medium speed, then perform left/right swing operations.
Once the system reaches normal operating temperature, reduce throttle to idle with the hydraulic lock engaged.
Closely monitor the pressure gauge or monitor readings, then gently move the joystick to initiate swing until the upper structure begins to rotate. Record the pressure value.
Repeat the same test in the opposite swing direction.
Compare and check the pressure values.
For CAT 320D2, the minimum swing motor starting pressure was 3,200 kPa.
For CAT 336D2, the minimum swing motor starting pressure was 3,800 kPa.
These are not manual values but actual field test results, which have significant meaning.
The OEM typically tests under maximum throttle, which may conceal certain faults. By contrast, my test method—at idle speed with light joystick input—can reveal hidden issues.
⚠️ Note: These data were obtained with the swing brake released, thus excluding the influence of the brake. If the swing brake cannot be released or is stuck, the starting pressure will be higher. Therefore, ensure the swing brake is disengaged before testing.
Valve plate leakage – Can be preliminarily judged by high starting pressure and unstable pressure build-up.
Incorrect swing relief valve setting – Usually set too low; excessive settings are rarely problematic.
Swing cushion valve leakage – Causes the upper structure to oscillate during swing.
Swing brake failure – Results in excessively high starting pressure and a “sticking” feel, similar to nine-hole plate jamming.
Another issue to watch for is excessive return back pressure. This often occurs after hydraulic system repairs when the return line and back-pressure valve are not properly cleaned. High back pressure can quickly damage the swing motor.
Each hydraulic motor must have a return line that ensures operation under very low back pressure (typically 300–500 kPa). The system must comply with the OEM’s specifications.
Additionally, swing motor output shaft seal failure may result from:
Main bearing failure, or
Metal debris generated by motor wear.
If you have the capability to measure swing motor leakage flow, using leakage volume as the basis for evaluating swing motor performance is the most accurate and reliable method.
ব্যক্তি যোগাযোগ: Mr. Paul
টেল: 0086-15920526889
ফ্যাক্স: +86-20-89855265