Air gap magnetic coupling with counterbalanced force

A pump assembly, comprising:

• a drive shaft rotatable on a drive axis;
• a driven shaft rotatable on the drive axis;
• a magnetic coupling assembly comprising:
• a drive magnet assembly coupled to the drive shaft, the drive magnet assembly comprising a first balancing magnet positioned on the drive axis, and a drive magnet coaxially positioned with the first balancing magnet;
• a driven magnet assembly coupled to the driven shaft, the driven magnet assembly comprising a second balancing magnet positioned on the drive axis, and a driven magnet coaxially positioned with the second balancing magnet, wherein:
• the drive magnet assembly is spaced from the driven magnet assembly by an axial gap, with the first balancing magnet facing the second balancing magnet across the axial gap, and the drive magnet facing the driven magnet across the axial gap;
• the drive magnet and the driven magnet are configured to drive rotation of the driven magnet in response to rotation of the drive magnet, and to generate an axial attractive force between the drive magnet and the driven magnet;
• and
• the first balancing magnet and the second balancing magnet are configured to generate an axial repulsive force between the first balancing magnet and the second balancing magnet that counterbalances the axial attractive force;
• a pump head comprising a fluid inlet, a fluid outlet, and a pumping stage, the pumping stage comprising a pump rotor communicating with the driven shaft,
• wherein rotation of the drive shaft drives rotation of the pump rotor via the magnetic coupling assembly, and the pumping stage is configured to pump fluid from the fluid inlet to the fluid outlet in response to the rotation of the pump rotor;
• a structural boundary disposed in the axial gap between the drive magnet assembly and the driven magnet assembly, wherein the structural boundary is composed of an electrically insulating material that is effective to prevent or minimize permeation of gases through the structural boundary including the fluid pumped by the pumping stage;
• and
• a casing enclosing the driven magnet assembly, wherein the casing comprises the structural boundary and is attached to or integrated with the pump head, and the casing at least partially defines a hermetic barrier configured to fluidly isolate the driven magnet assembly and at least part of the pump head from an ambient outside the casing.