Hydraulic excavator drive system

A hydraulic excavator drive system comprising:

• a first pump;
• a second pump;
• an arm cylinder;
• an arm first control valve connected to the first pump and a tank, and connected to the arm cylinder by an arm crowding supply line and an arm pushing supply line;
• an arm second control valve connected to the second pump and the tank, connected to the arm crowding supply line by a first replenishment line, and connected to the arm pushing supply line by a second replenishment line;
• and
• an arm operation device including an operating lever that receives an arm crowding operation and an arm pushing operation, the arm operation device outputting an operation signal corresponding to an inclination angle of the operating lever, wherein
• the arm second control valve is configured such that, at a time of performing the arm crowding operation,
• an opening area at a meter-in side, which is the first replenishment line side, of the arm second control valve changes in accordance with the operation signal, and
• an opening area at a meter-out side, which is the second replenishment line side, of the arm second control valve is:
• kept to zero in a case where a predetermined condition is not satisfied;
• and
• kept to zero when the operation signal is a setting value or less, and when the operation signal is mater than the setting value, increases to a maximum value in a case where the predetermined condition is satisfied.