An apparatus for actuating a pressure delivery system of a fluid sampler. The apparatus includes a housing (302) having a longitudinal passageway and defining first and second chambers (338, 348). A piston (346) is disposed within the longitudinal passageway between the first and second chambers (338, 348). A valving assembly (356) is disposed within the longitudinal passageway. The valving assembly (356) is operable to selectively prevent communication of pressure from a pressure source of the fluid sampler to the second chamber (348). The valving assembly (356) is actuated responsive to an increase in pressure in the first chamber (338) which longitudinally displaces the piston (346) toward the valving assembly (356) until at least a portion of the piston (346) contacts the valving assembly (356), thereby releasing pressure from the pressure source into the second chamber (348) and longitudinally displacing the piston (346) away from the valving assembly (356).