Printer with ink supply system having downstream conduit loop

1. A printer comprising:

a printhead having an ink inlet and an ink outlet;

a pressure-regulating chamber having an outlet port connected to said ink inlet via an upstream ink conduit, said chamber containing ink at a first level below said printhead, wherein a headspace above said first level of ink is open to atmosphere; and

a downstream ink conduit connected to said ink outlet and terminating above said first level of ink, said downstream ink conduit being open to atmosphere,

wherein said downstream ink conduit comprises a loop section passing below said first level of ink, such that, in a printing configuration, a second level of ink in said loop is equal to said first level of ink in said chamber.

2. The printer of claim 1 comprising means for maintaining a predetermined first level of ink in said chamber, said predetermined first level of ink controlling a hydrostatic pressure of ink supplied to said ink inlet.

3. The printer of claim 2 , wherein said hydrostatic pressure, relative to atmospheric pressure, is defined as ρgh, wherein ρ is the density of ink, g is acceleration due to gravity and h is the height of the predetermined first level of ink relative to the printhead.

4. The printer of claim 2 , wherein said means for maintaining said predetermined first level of ink comprises an ink reservoir cooperating with a float valve contained in said pressure-regulating chamber.

5. The printer of claim 4 , wherein said float valve comprises:

an arm pivotally mounted about a pivot;

a float mounted at one end of said arm; and

a valve head mounted at an opposite end of said arm,

wherein said valve head is positioned for sealing engagement with a valve seat at an inlet port of said pressure-regulating chamber.

6. The printer of claim 5 , wherein said inlet port and said outlet port of said pressure-regulating chamber are positioned towards a base of said chamber.

7. The printer of claim 1 , further comprising a printhead priming system.

8. The printer of claim 7 comprising:

an air pump communicating with said headspace above said ink in said chamber; and

a valve positioned between said ink reservoir and said inlet port,

wherein, in a priming configuration, said valve is configured to be shut and said pump is configured to positively pressurize said headspace thereby forcing ink from said chamber into said downstream ink conduit.

9. The printer of claim 8 , wherein a sensor is positioned for sensing ink towards a terminus of said downstream ink conduit, said sensor cooperating with said pump such that said pump is shut off when said sensor senses any ink.

10. The printer of claim 8 , wherein said loop section controls an amount of ink flowing from said downstream ink line back into said pressure-regulating chamber so as to restore said printing configuration after priming.

11. The printer of claim 9 , wherein said sensor is an optical sensor.

12. The printer of claim 9 , further comprising means for minimizing phantom sensing of ink caused by ink bubbles in said downstream ink line.

13. The printer of claim 12 comprising a bubble-bursting box, said box comprising:

at least one bubble-bursting chamber having a respective chamber inlet; and

an air outlet.

14. The printer of claim 13 , wherein said air outlet is open to atmosphere or said air outlet communicates with a pump inlet of said air pump.

15. The printer of claim 13 , wherein said at least one bubble-bursting chamber is dimensioned to promote expansion and bursting of ink bubbles entering said chamber via said chamber inlet.

16. The printer of claim 15 , wherein said bubble-bursting box comprises a plurality of bubble-bursting chambers, each chamber corresponding to a respective ink channel of said printer.

17. The printer of claim 13 , wherein said bubble-bursting box comprises an air chamber in fluid communication with said at least one bubble-bursting chamber via an air channel defined in a roof of said box, said air outlet being defined in said air chamber.

18. The printer of claim 17 , wherein said air channel is a hydrophobic serpentine channel comprising at least one ink-trapping stomach, said air channel minimizing transfer of ink to said air chamber when said box is tipped.

19. The printer of claim 8 , wherein said pump is a reversible pump.

20. The printer of claim 19 , wherein, in a de-priming configuration, said pump is reversed and ink is pulled from said printhead towards said pressure-regulating chamber.