A maintenance technician with over ten years of experience in Hydraulic Pump repair work undertook the repair job of an A4VG180 pump used in a concrete pump truck.

He purchased a brand new China made barrel and port plate from one Chinese factory which was lapped also by the factory before shipping. When he received the barrel and port plate, he carefully inspected the flow surfaces of the barrel and port plate to confirm that they had been ground. However, he still decided to use a marking paste to verify the matching accuracy of the friction pair. Indeed, he found two parallel marks on the flow surface of the barrel, so he proceeded to assemble it confidently, installing the pump on the test bench to begin testing.

When the A port is loaded, as the pressure at the A port rises, the leakage from the pump casing increases with the pressure. When the pressure at the A port approaches 200 bar, the flow at the A port is basically below 80L, while the leakage from the pump casing exceeds 100 liters.

With doubts, he disassembled the pump and found the following situation: