Intermediate fluid supply apparatus having flexible membrane

A fluid-ejection device comprising:

• a primary fluid supply to store fluid;
• one or more fluid-ejection printheads to eject the fluid in a desired manner;
• and,
• an intermediate fluid supply apparatus to fluidically couple the primary fluid supply to the fluid-ejection printheads, the fluid ejected by the fluid-ejection printheads received from primary fluid supply via the intermediate fluid supply apparatus, the intermediate fluid supply apparatus comprising:
• a reservoir having a bottom surface and a plurality of side surfaces and open at a top of the reservoir, to store fluid supplied by the primary fluid supply for ejection by the fluid-ejection printheads;
• a flexible membrane sealing the top of the reservoir and parallel to an imaging surface onto which the fluid-ejection printheads are to eject the fluid, the flexible membrane to expand and contract over the reservoir in accordance with a volume of the fluid currently stored within the reservoir;
• and,
• a sensing mechanism to sense directly or indirectly the volume of the fluid currently stored within the reservoir,
• wherein the flexible membrane is to expand and contract over the reservoir unassisted by any other component of the intermediate fluid supply apparatus, and the flexible membrane is connected within the intermediate fluid supply apparatus just to the side surfaces of the reservoir.