Carpenter, 25, was acquired by the Astros a year ago from the Cardinals in exchange for third baseman Pedro Feliz. He split time with Double-A Corpus Christi and Oklahoma City this season, going 0-1 with a 1.91 ERA with 38 strikeouts in 33 relief outings.
"We like those 0.00 ERA guys a lot," Astros general manager Ed Wade said. "We paid attention to what he was doing at Double-A and figured that he was ready for the challenge of Triple-A."
The Astros have been waiting on Carpenter to further develop his slider, and Oklahoma City pitching coach Burt Hooton said in his game report a few days ago that Carpenter threw three outstanding sliders and had figured it out.
"That sort of shined a little bit of a bright light on David in the short term," said Wade, who added that Fernando Rodriguez -- who was optioned June 25 to make room for an extra catcher -- had to spend at least 10 days in the Minor Leagues before he could recalled.
With Carpenter coming aboard to put the Astros' bullpen back at full strength with seven arms, catcher Brian Esposito was optioned to Oklahoma City. Esposito was called up as protection at catcher, where J.R. Towles had been unavailable to play defense since Friday because of a chin laceration.