If you ever start an excavator in the morning, pull the boom lever, and hear a high-pitched, gravelly screaming sound coming from the back of the machine, shut it off immediately. You are hearing cavitation, and every second that sound happens, it's destroying your main hydraulic pump.
A lot of mechanics misdiagnose cavitation as a failing pump bearing. But cavitation isn't a mechanical wear issue; it's a fluid dynamics issue. It happens when the pump is trying to pull hydraulic oil in faster than the supply line can deliver it. When this happens, microscopic vacuum bubbles form in the oil. As those bubbles pass into the high-pressure side of the pump, they violently implode. These implosions literally blast microscopic chunks of metal off the internal gears or pistons.
Before you condemn a $6,000 pump, check three things. First, check the hydraulic tank suction strainer. If it's clogged with debris from a failing cylinder seal, the pump will starve. Second, check the hydraulic oil level-obviously, but do it with the boom all the way down and the dipstick fully seated, as low oil is the leading cause. Third, and most commonly overlooked: check the O-rings on the suction line going from the tank to the pump. If there is even a pinhole leak in that suction hose, it will suck air instead of oil. Air compresses, oil doesn't, and that air compression causes the exact same cavitation damage. Fix the air leak or clean the strainer, bleed the air out of the system, and that screaming noise will disappear, saving your pump.
