<p>The abrupt interruption due to the closure of the valve during the gravity-driven drainage of a liquid and granular medium results in the backflow of materials, which is widely encountered during pneumatic conveying. This phenomenon bears a strong resemblance to the classical water hammer effect, which is reported for the first time by the present authors in “Backward flow and jet formation of liquid and granular medium in a gravity drainage system following a sudden valve closure”, Powder Technology, Volume 438 (2024). Under specific conditions, one may encounter jet formation at the free surface. The current article produces a computational investigation on the effect of the rate of contraction on the backflow of materials and jet formation. Detailed parametric research is executed to characterize and compare the phenomenon for both the flowing medium,—liquid, and granular matter with the variation of rate of contraction. The Rayleigh Plateau instability led interesting phenomenon of jet rupture is also articulated in this article during the collapse of the long liquid jet at a lower level of rate of contraction (r (as described in Eq.&#xa0;18) &lt; 1). The current article addresses the effect weber number (We) on the jet rupture and energy dissipation due to jet rupture during the collapse of it. The present article also introduces the formation of a hollow granular jet at a lower level of r (r = 0.27) due to the introduction of a long reducer between the drainage tube and the extension line and drastic reduction of bulk density of the jet. The investigation is further extended to understand and differentiate the evolution and collapse of hollow and solid jet. The comparison of the energy dissipation during the formation and collapse of both the jets is studied too.</p> Graphical Abstract <p></p>