Failure of the variable mechanism may manifest as an inability to adjust the flow or unstable adjustment. First check whether the control oil circuit is blocked. If necessary, flush the system and replace the clean oil. Wear of the variable head and variable body will lead to inaccurate control and need to be scraped and repaired. When the servo valve core, differential piston or spring core shaft is stuck, if it is mechanically stuck, you can try to grind and repair it. If it is due to oil contamination, the oil should be replaced and the system should be cleaned. For electronically controlled variable pumps, it is also necessary to check whether the electrical signal and control circuit are normal. During regular maintenance, special attention should be paid to the lubrication and cleaning of the variable mechanism to prevent impurities from entering the precision matching surface.