Heat tomato juice and water in cooker. Drop meatballs into juice mixture.
Close cover and place pressure regulator on pipe, cook for 10 minutes with pressure regulator rocking slowly. In other words, secure pressure cooker lid properly, bring the heat up to begin the regulator rocking and when that begins lower the heat until the regulator rocks slowly.
Remove from heat and let pressure drop by itself. Use precaution and open the lid away from yourself after the pressure cooker valve stops steaming.