Why is a very close fit necessary between the teeth, and between the teeth and the casing on a gear pump?

A very close fit between the teeth of a gear pump and between the teeth and the casing is essential primarily to prevent bypassing back to the inlet. In gear pumps, the function relies heavily on the tight sealing between the gears and other components to create a high-pressure zone that effectively moves fluid through the system. If there is excessive clearance or a poor fit, the fluid can leak back into the inlet side, leading to a loss of efficiency and a decrease in the pump's ability to maintain pressure.

Maintaining this close fit ensures that the fluid displacement is maximized and that it is directed properly through the discharge port without unintended recirculation. This helps in achieving optimal performance and consistent flow rates, which are crucial for the system's overall effectiveness.