Float valve sub

A float valve sub comprising:

• an outer tube assembly;
• and
• a float valve assembly arranged detachably in an inside of the outer tube assembly,
• wherein the float valve assembly comprises:
• a first end section having a cylindrical shape;
• a second end section having a cylindrical shape;
• a valve assembly middle section arranged between the first end section and the second end section;
• and
• a lid section attached to the first end section,
• wherein the lid section moves turnably between a first position for closing a passage of the first end section and a second position for opening the passage of the first end section,
• wherein the valve assembly middle section has a side opening through which a part of the lid section is possible to pass,
• wherein the outer tube assembly comprises:
• a first section having an inner circumference surface complementary to an outer circumference surface of the first end section to receive the first end section;
• a second section having an inner circumference surface complementary to an outer circumference surface of the second end section to receive the second end section;
• and
• an outer tube assembly middle section arranged between the first section and the second section,
• wherein the outer tube assembly middle section has a concave section possible to receive the lid section in the second position,
• wherein a minimum inner diameter of the first section is larger than that of the second section, and
• wherein an inner diameter of the concave section is larger than the minimum inner diameter of the first section.