A sand and gravel plant reported that a Case 821G wheel loader's lift arms felt "spongy" and took 10 seconds to raise a full bucket. The hydraulic oil in the sight glass looked milky white.
The technician first checked the "Pump Case Drain Flow." The flow was high, indicating internal wear, but the milky oil suggested "Aeration" (air mixing with oil) rather than just wear. He inspected the "Hydraulic Tank Suction Strainer." The strainer mesh was torn, and the internal magnet was loose.
He removed the hydraulic tank cover. Inside the tank, the "Anti-Swirl Baffle Plate" (a metal plate designed to stop oil from swirling and creating a vortex) had a cracked weld. The cracked baffle allowed the returning oil to swirl, creating a vortex over the suction port. The pump was sucking a mixture of oil and air (cavitation). The air bubbles imploded inside the pump, destroying the internal components of the gear pump and causing the spongy, slow lift.
The repair involved welding the cracked baffle plate inside the tank. The tank was thoroughly cleaned, and a new suction strainer was installed. The hydraulic pump was replaced (the internal damage from cavitation was too severe). After refilling with fresh ISO 68 oil and purging the air, the lift arms responded instantly and firmly.
