HOUSTON—Astronauts tinkered Sunday with a troublesome piece of equipment designed to help convert urine and sweat into drinkable water, which is vital to allowing the international space station crew to double to six.

Station commander Michael Fincke and space shuttle Endeavour astronaut Donald Pettit changed how a centrifuge is mounted in a urine processor, which is part of the newly delivered $154 million water recovery system. The centrifuge is a spinning device that helps separate the water from urine.

It was on rubber grommets to reduce vibrations, and Mission Control asked Fincke to remove them and just bolt the piece down.

“We’re very hopeful for this, and if not, we have a few other tricks up our sleeves,” Fincke said from the space station after the task was finished.

Flight controllers were heartened Sunday evening that the first test after the repairs showed no immediate problems. As a last resort, Endeavour could bring the problematic part back to Earth for repairs when the shuttle departs on Thanksgiving. That option could complicate plans to add crew members to the station since several water samples need to brought back for tests before astronauts can drink from the contraption. Samples will be brought back on Endeavour and in February on space shuttle Discovery.

The astronauts have been trying to get the system running for four days, but the urine processor has worked for just two hours at a time before shutting down. A normal run is about four hours. The water recovery system, delivered a week ago by Endeavour, is essential for allowing six astronauts to live on the space station by the middle of next year.