A valve assembly (300) is adapted to be coupled with a flexible pipe (200). The valve assembly (300) includes a hollow body (310) defining a first end (320) and a second end (330). A porous body (350) partially encloses the hollow body (310) proximate to the first end (320) and houses a swellable material (344). The hollow body (310) further defines a hollow chamber (340) between the first and second ends (320, 330). A piston (346) is disposed within the hollow chamber (340). The piston (346) is adapted to move between a first position (P1) and a second position (P2) corresponding to a contraction and an expansion of the swellable material (344). The valve assembly (300) selectively allows passage of water through the flexible pipe (200) based on the positions (P1. P2) of the piston (346). The irrigation system (100) is characterized in that the valve assembly (300) further includes an elastic diaphragm (380) disposed between the swellable material (344) and the piston (346). The elastic diaphragm (380) includes an annular bead (382).