Ink supply system and ink-jet recording apparatus

An ink supply system comprising:

• a main tank;
• an ink jet head including a subtank;
• an ink supply channel which is connected to said main tank and which is connectable to and separable from said subtank;
• pressure reduction means which is connectable to and separable from said subtank for reducing the pressure inside said subtank;
• and
• an opening/closing mechanism which controls flow of ink from said main tank to said subtank, wherein said opening/closing mechanism opens when a state of pressure reduction inside said subtank is the same as or more than a predetermined threshold and closes when the state of pressure reduction is less than the threshold;
• wherein while said ink supply channel and said subtank are connected to each other, said pressure reduction reaches or exceeds the threshold, so that said opening/closing mechanism opens to initiate an ink supply operation from said main tank to said subtank, and
• while the connection between said ink supply channel and said subtank is maintained, said opening/closing mechanism closes when the state of pressure reduction inside said subtank is reduced to less than the threshold thereby completing the ink supply operation.