Precision liquid injection system

A liquid injector, comprising;

• a tubular spindle having a longitudinal axis, an open end, and an opposing partially closed end, the spindle open end and spindle closed end defining a cylindrical bore along the longitudinal axis of the spindle;
• cylindrical piston within the spindle bore axially aligned with the longitudinal axis of the spindle;
• sealing means between the spindle and the piston, the spindle, piston and sealing means defining a chamber between the piston and the spindle closed end within the bore;
• a tubular driver sleeve having a longitudinal axis, an open end and opposing closed end, the driver sleeve having threads around an interior surface of the sleeve and the spindle having compatible threads around an exterior surface of the spindle such that rotation of the driver sleeve in one direction screws the driver sleeve towards the spindle closed end to cause the piston to move towards the spindle closed end and exert pressure on the chamber;
• ratchet means for controlling the degree of rotation of the driver sleeve and providing a positive indication of driver sleeve rotation;
• and
• means for manually releasing the ratchet means,
• wherein the ratchet means comprises:
• a plunger bore in the end of the piston that corresponds to the closed end of the tubular driver sleeve;
• a plunger member located within the plunger bore;
• at least one ratchet bore in the closed end of the tubular driver sleeve;
• and
• a spring located within the plunger bore for applying a force to the plunger member to cause the plunger member to engage the ratchet bore when the plunger bore and ratchet bore are brought into alignment by the rotation of the driver sleeve.