Abstract: A hydraulically and/or pneumatically actuated cutting tool is provided having a housing with a piston assembly slidably disposed between a fluid inlet and a fluid outlet. The piston assembly comprises a seal which is operable between two positions. In a first position the seal produces a substantially water-tight seal between the piston and the interior surface of the housing. As a result, fluid entering the chamber through the fluid inlet advances the piston assembly toward the fluid outlet. In a second position a gap is formed between the seal and the interior surface of the housing such that fluid communication is established between the fluid inlet and the fluid outlet. As the fluid is removed from the housing through the fluid outlet, a spring biases the piston assembly back to its original resting position.