Abstract: A valve which allows the rapid discharge of a fluid from a reservoir (13) to a working volume (12) includes a housing (10) and a cylindrical sleeve (14) movable axially within the housing between a closed position in which it separates the reservoir (13) from the working volume (12) and an open position in which the reservoir (13) communicates with the working volume (12). Sealing means (20, 21) are provided to prevent leakgage of the fluid when the sleeve is in the closed position. Actuating means are provided for moving the sleeve (14) between its two positions. The sealing means comprises seals (20, 21) located to engage one end (19) of the sleeve around the outer and inner peripheries respectively when the sleeve (14) is in the closed position.