Piston seal structure for injector

1. A piston-cylinder structure, comprising:

a cylinder;

an end cap;

a tapered portion for extruding dead space;

an upper bowl-shaped seal portion;

a columnar seal portion;

a lower bowl-shaped seal portion; and

a piston push rod;

wherein the end cap is fixed on a top of the cylinder; a casing of the end cap is made of a corrosion-resistant metal material or a non-metallic material; a lining of the end cap is made of polytetrafluoroethylene (PTFE); the end cap has a funnel-shaped inner cavity to reduce dead volume of an inner cavity of the cylinder;

the piston push rod is made of PEEK; an upper portion of the piston push rod is cylindrical; an outer diameter of the upper portion of the piston push rod is smaller than a diameter of a bowl bottom of the upper bowl-shaped seal portion and a diameter of a bowl bottom of the lower bowl-shaped seal portion; an outer diameter of a lower portion of the piston push rod is larger than that of the upper portion of the piston push rod, and is smaller than an inner diameter of the cylinder;

the upper portion of the piston push rod sequentially passes through the lower bowl-shaped seal portion, the columnar seal portion and the upper bowl-shaped seal portion, and is fixedly connected to the tapered portion; the piston push rod is configured to fix the lower bowl-shaped seal portion, the columnar seal portion, the upper bowl-shaped seal portion and the tapered portion, and drive the lower bowl-shaped seal portion, the columnar seal portion, the upper bowl-shaped seal portion and the tapered portion to reciprocate in the cylinder;

the tapered portion is made of PTFE or PEEK; an upper portion of the tapered portion fits the funnel-shaped inner cavity of the end cap in shape; a lower portion of the tapered portion fits the upper bowl-shaped seal portion in shape; the tapered portion is configured to expel liquid in the cylinder when the upper portion of the tapered portion moves to the end cap so as to reduce the dead space in the inner cavity of the cylinder;

the upper bowl-shaped seal portion is provided below the tapered portion; the upper bowl-shaped seal portion is made of PEEK; a bowl opening of the upper bowl-shaped seal portion faces toward the tapered portion; the upper bowl-shaped seal portion is configured to form an effective seal between the piston push rod and the cylinder when the piston push rod moves toward the end cap and to remove crystals on an inner wall of the cylinder;

the columnar seal portion is provided below the upper bowl-shaped seal portion and above the lower bowl-shaped seal portion; the columnar seal portion is made of PTFE; a difference between an outer diameter of the columnar seal portion and the inner diameter of the cylinder is 10-20 μm;

the columnar seal portion is configured to enable the piston push rod to be coaxial with the cylinder, and to provide a mechanical support for the piston push rod; the columnar seal portion provides an auxiliary sealing when the piston push rod reciprocates along the cylinder, and provides a mechanical support for the upper bowl-shaped seal portion and the lower bowl-shaped seal portion to prevent fluid leakage in the upper bowl-shaped seal portion and the lower bowl-shaped seal portion under overpressure;

the lower bowl-shaped seal portion is provided below the columnar seal portion; the lower bowl-shaped seal portion is made of PEEK; a bowl bottom of the lower bowl-shaped seal portion faces toward the columnar seal portion; and the lower bowl-shaped seal portion is configured to provide sealing between the piston push rod and the cylinder and remove the crystals on the inner wall of the cylinder when the piston push rod moves toward the end cap.

2. The piston-cylinder structure of claim 1 , wherein the corrosion-resistant metal material comprises stainless steel; and the non-metallic material comprises PEEK.

3. The piston-cylinder structure of claim 1 , wherein the piston push rod is fixed to the tapered portion by mechanical riveting.

4. The piston-cylinder structure of claim 1 , wherein a thickness of a side wall of the upper bowl-shaped seal portion decreases from the bowl bottom to the bowl opening thereof; the side wall of the upper bowl-shaped seal portion at the bowl opening has a thickness of 0.3-1.0 mm; a difference between an outer diameter of the bowl opening of the upper bowl-shaped seal portion and the inner diameter of the cylinder is 10-20 μm; and the upper bowl-shaped seal portion fits the lower portion of the tapered portion.

5. The piston-cylinder structure of claim 1 , wherein the piston push rod and the upper bowl-shaped seal portion are fixed by mechanical riveting.

6. The piston-cylinder structure of claim 1 , wherein the piston push rod and the columnar seal portion are fixed by mechanical riveting.

7. The piston-cylinder structure of claim 1 , wherein a thickness of a side wall of the lower bowl-shaped seal portion decreases from the bowl bottom to a bowl opening thereof; the side wall of the lower bowl-shaped seal portion at the bowl opening has a thickness of 0.3-1.0 mm; and a difference between an outer diameter of the bowl opening of the lower bowl-shaped seal portion and the inner diameter of the cylinder is 10-20 μm.

8. The piston-cylinder structure of claim 1 , wherein the piston push rod and the lower bowl-shaped seal portion are fixed by mechanical riveting.