Patent ID: 7475797

Claim:
A liquid supply apparatus, comprising: an elongated cylinder including a head portion with an opening, and an open rear portion; a piston which is inserted into the cylinder and hermetically divides an inner space of the cylinder into a liquid compartment on the side of the head portion and a gas compartment on the side of the rear portion; a gas supply apparatus connected to the rear portion of the cylinder and constructed to supply the gas compartment with gas such that the piston is moved toward the head portion when the gas is supplied to the gas compartment; wherein the piston comprises a body and a sealing ring which surrounds the body and is in contact with an inner surface of the cylinder, and the sealing ring comprises an inner base fixed to the body and an outer wing which is connected to the base and is in contact with the inner surface of the cylinder; wherein the piston comprises at least two sealing rings, and the outer wing of one of the sealing rings on a side of the liquid compartment extends toward the liquid compartment and the outer wing of the other sealing ring on a side of the gas compartment extends toward the gas compartment; and wherein a sealing ring on a side of the liquid compartment and a sealing ring on a side of the gas compartment are sealing rings with a substantially identical dimension, and a radius of the bottom of the groove in the piston body into which the sealing ring on the side of the gas compartment is fitted is larger than that of the bottom of the groove into which the sealing ring on the side of the liquid compartment is fitted.