Which of the following is NOT a type of gear pump?

A vane pump is distinct from gear pumps, as it operates based on a different principle. Vane pumps use sliding vanes to create a chamber that fluctuates in size, generating a pumping action as the vanes move in and out of their slots. This mechanism is fundamentally different from the operation of gear pumps, which utilize interlocking gears to move fluid.

Gear pumps, including both external and internal types, function by trapping fluid between the gears and moving it through the pump as the gears turn. Screw pumps, while also not gear pumps, are a separate category that uses a helical screw mechanism for fluid movement. Understanding these distinctions helps in recognizing the specific categories and functions within hydraulic systems.