Abstract: Apparatus for preventing the unwanted extension of a hydraulic lock when the lock is subjected to relatively high dynamic loads. The lock includes a hydraulic cylinder having a piston slidably mounted therein. The piston is secured to a piston rod which passes outwardly through one end wall of the cylinder. The lock is placed in tension when the piston rod is being extended and in compression when the rod is being retracted. A flow channel is formed in the piston through which fluid is exchanged from one side of the piston to the other. A manually operated spring biased control valve is mounted in the flow channel which is normally held closed by a set spring. Fluid is allowed to flow when the valve is manually opened or when the lock is placed in tension by some external force that overcomes the biasing force of the set spring. A velocity sensitive restrictor is also mounted in the flow channel that closes the channel when the lock is placed in tension by a dynamic force above a predetermined velocity.