Patent ID: 7699451

Claim:
A pressure retaining device for retaining a pressure in a communication passage which are communicated between a supply tank for supplying a first fluid and a nozzle for ejecting the first fluid, comprising: a compressing unit provided across an intermediate of the communication passage for compressing the first fluid transferred from the supply tank to the nozzle; a pump for supplying to the compressing unit a second fluid on which a pressure is loaded thereby; a reservoir, through which the compressing unit is communicated to the pump, for holding the second fluid supplied by the pump; a relief valve provided on the reservoir for releasing an inner pressure in the reservoir; a control valve provided between the compressing unit and the reservoir for controlling supply of the second fluid from the reservoir to the compressing unit; and a controller capable of performing operation of: closing the relief valve; closing the control valve; supplying the second fluid to the reservoir by the pump for a predetermined period of time; opening the control valve for a predetermined period of time to compress the first fluid in the compressing unit; and opening the relief valve; wherein the second fluid is supplied by the pump to the compressing unit to compress the first fluid in the compressing unit; and wherein the first fluid in the nozzle is then compressed by a pressure loaded on the first fluid in the compressing unit.