Apparatus for sealing a puncture communicating with a blood vessel includes an introducer sheath, an occlusion member with a balloon thereon, a retraction assembly, and a syringe assembly including sealing material therein. The syringe assembly may include a pair of syringe barrels having sealing components therein, and a plunger assembly biased to slide within the barrels from proximal to distal positions for injecting the components through outlets of the barrels. An auto-injector assembly may be coupled to the plunger apparatus, and includes a spring mechanism locked in an inactive condition and an actuator activatable to release the spring mechanism, whereupon the spring mechanism automatically advances the plunger assembly towards the distal position to inject the components from the barrels.
