The invention relates to a stop wedge for a stop valve, which is designed to be moved in translation along a displacement axis (T-T). The wedge consists of a sealing panel comprising a distal end (60) which is intended to be applied against a sealing seat (22) and two lateral guide elements (82, 84). The stop wedge (6) also comprises a stopping surface (A) which comes into contact with the pressurised liquid and which is projected onto the displacement plane (C-C) when the stop wedge (6) is in the closed position. The distal ends (98, 100) of the aforementioned guide elements (82, 84) are separated from the distal end (60) of the stop wedge (6) by a distance dp which is measured along the displacement axis (T-T). The stopping surface (A) has a height H along the displacement axis (T-T), while the dp/H ratio is less than 0.34.