A mining operator reported that a Komatsu PC200-8M0 excavator's hydraulic system made a loud "grinding" noise (cavitation sound) when the boom was raised. The engine also vibrated heavily.
The technician checked the "Hydraulic Tank Breather Cap." The cap was missing the "Air Filter Element," and the hole was plugged with mud. This created a vacuum in the tank as the cylinders retracted. He then checked the "Main Pump Suction Hose." The hose clamp was loose, and the hose fitting was rusty.
The loose fitting and plugged breather allowed air to be sucked into the pump intake. The pump was "cavitating" (imploding air bubbles), creating the grinding noise and sending shockwaves through the hydraulic lines. These shockwaves caused the engine mounts to vibrate.
The repair involved cleaning the breather cap and replacing the filter element. The suction hose flange was cleaned, sealed with O-ring grease, and tightened. The hydraulic tank was pressurized slightly (per manual spec) to test for leaks. After starting, the cavitation noise disappeared, and the engine ran smoothly.
