Multistage air pump

A multistage air pump comprising:

• a cylinder assembly having
• a cylinder having a front end and a rear end;
• a rear cap mounted on the rear end of the cylinder and having
• a through hole;
• and
• an inner sidewall formed around the through hole of the rear cap;
• a sealing ring mounted on and around the inner sidewall of the rear cap;
• and
• at least one inlet one-way mechanism mounted in the rear cap and disposed around the through hole of the rear cap;
• a surrounding piston assembly slidably mounted through the through hole of the rear cap and having
• a surrounding rod slidably mounted through the through hole of the rear cap, abutting the sealing ring of the cylinder assembly, and having
• an inner end protruding in the cylinder;
• an outer end protruding out of the cylinder;
• and
• a sliding channel axially formed between the inner end of the surrounding rod and the outer end of the surrounding rod;
• a surrounding piston formed on the inner end of the surrounding rod and having
• a through hole axially formed through the surrounding piston and communicating with the sliding channel of the surrounding rod;
• an inner sidewall formed around the through hole of the surrounding piston;
• an outer sidewall;
• a distal end;
• and
• a proximal end attached to the surrounding rod;
• a second end cap mounted on the outer end of the surrounding rod and having an air channel axially formed through the second end cap and coaxial with a longitudinal axis of the surrounding rod;
• an inner sealing ring mounted on and around the inner sidewall of the surrounding piston;
• and
• an outer sealing ring mounted on and around the outer sidewall of the surrounding piston and abutting the cylinder;
• and
• an outlet one-way mechanism mounted in the air channel of the second end cap;
• two one-way mechanisms respectively disposed between the proximal end of the surrounding piston and the outer sealing ring of the surrounding piston assembly, and between the distal end of the surrounding piston and the outer sealing ring of the surrounding piston assembly;
• an inner piston assembly mounted on the cylinder and having
• an inner rod axially mounted in the cylinder, mounted through the through hole of the surrounding piston, and abutting the inner sealing ring of the surrounding piston assembly, and the inner rod having
• an inner end protruding in the sliding channel of the surrounding rod;
• and
• an outer end;
• an inner piston formed on the inner end of the inner rod;
• a first end cap mounted on the front end of the cylinder and connected to the outer end of the inner rod;
• at least one one-way mechanism mounted in the inner piston;
• at least one inlet one-way mechanism mounted in the first end cap;
• a first chamber defined in the cylinder and between the rear cap and the surrounding piston;
• a second chamber defined in the sliding channel of the surrounding rod and between the surrounding piston and the inner piston;
• a third chamber defined in the sliding channel of the surrounding rod and between the surrounding piston and the second end cap;
• a fourth chamber defined in the cylinder and between the first end cap and the surrounding piston;
• wherein the air channel of the second end cap directly communicates with the third chamber and communicates with an exterior of the multistage air pump via the outlet one-way mechanism of the surrounding piston assembly;
• wherein the at least one inlet one-way mechanism that is mounted in the rear cap only allows air outside the multistage air pump to flow into an interior of the cylinder;
• the outlet one-way mechanism of the surrounding piston assembly only allows air inside the third chamber to flow to the exterior of the multistage air pump;
• the at least one one-way mechanism of the inner piston assembly only allows air inside the second chamber to flow into the third chamber;
• the one-way mechanism that is disposed between the proximal end of the surrounding piston and the outer sealing ring of the surrounding piston assembly only allows air inside the first chamber to flow into the second chamber;
• the one-way mechanism that is disposed between the distal end of the surrounding piston and the outer sealing ring of the surrounding piston assembly only allows air inside the fourth chamber to flow into the second chamber;
• and
• the at least one inlet one-way mechanism of the inner piston assembly only allows the air outside the multistage air pump to flow into the fourth chamber;
• wherein when the inner piston assembly is pulled, the air inside the first chamber is compressed and flows into the second chamber, the air inside the second chamber is compressed and flows into the third chamber, and the air outside the multistage air pump flows into the fourth chamber;
• when the inner piston assembly is pushed, the air outside the multistage air pump flows into the first chamber, the air inside the fourth chamber is compressed and flows into the second chamber, and the air inside the third chamber is compressed and flows out of the multistage air pump via the outlet one-way mechanism of the surrounding piston assembly for inflation.