Dialysis systems having air separation chambers with internal structures to enhance air removal

A dialysis fluid cassette comprising:

• a rigid portion defining at least one valve chamber;
• the rigid portion further defining an air separation chamber, the air separation chamber when in an operating position including a first sidewall and a second sidewall, a first fluid opening, a second fluid opening, and a separation wall extending from the first sidewall to the second sidewall, the separation wall having a free edge residing within the air separation chamber, the separation wall forcing the dialysis fluid to flow from one of the fluid openings around the free edge of the separation wall to the other of the openings, the separation wall tapered or angled to allow a cross-sectional area of a dialysis fluid pathway defined in part by the separation wall to increase as the dialysis fluid flows along the pathway, to slow the flow of dialysis fluid, allowing buoyancy forces to remove air from the dialysis fluid.