Pressure-regulating chamber comprising float valve biased towards closure by inlet ink pressure

1. A pressure-regulating chamber for maintaining ink contained therein at a predetermined first level relative to a printhead, said chamber comprising:

an inlet port for connection to an ink reservoir via an ink supply line;

an outlet port for connection to an ink inlet of a printhead via an upstream ink line;

an air vent open to atmosphere, said air vent communicating with a headspace above said ink; and

a float valve for maintaining said predetermined first level of ink by controlling a flow of ink into said inlet port, wherein said float valve is biased towards a closed position by a positive ink pressure at said inlet port, wherein said float valve comprises:

an arm pivotally mounted about a pivot;

a float mounted at one end of said arm; and

a valve stem attached to said arm, said valve stem having a valve head for closure of a valve seat, said valve seat being positioned at the inlet port of said pressure-regulating chamber.

2. The pressure-regulating chamber of claim 1 , wherein said valve head comprises an umbrella sealing cap for closure of the valve seat.

3. The pressure-regulating chamber of claim 2 , wherein an outer surface of a base of said chamber comprises said valve seat.

4. The pressure-regulating chamber of claim 3 , wherein said float valve is configured such that downward movement of said valve stem towards said base unseats said umbrella cap from said valve seat.

5. The pressure-regulating chamber of claim 4 , wherein said positive ink pressure at said inlet port urges said umbrella sealing cap against said valve seat.

6. The pressure-regulating chamber of claim 5 , wherein the positive ink pressure is provided by said ink reservoir positioned above said chamber.

7. The pressure-regulating chamber of claim 1 , wherein said valve stem is positioned between said pivot and said float.

8. The pressure-regulating chamber of claim 1 , wherein said inlet port and said outlet port are positioned towards a base of said chamber.

9. The pressure-regulating chamber of claim 1 , comprising a return port positioned at a base of said chamber.

10. The pressure-regulating chamber of claim 1 , wherein said air vent comprises an air-permeable membrane, which is impervious to ink.

11. The pressure-regulating chamber of claim 1 , wherein said return port comprises an inline ink filter.