Big, metallic and green, the mysterious machine formerly located between Calhoun and Berkeley colleges was removed from campus Tuesday as silently as it arrived more than three weeks ago.

The device was not a generator, some kind of new abstract art in the vein of Morse College’s famous Lipstick sculpture or even, as David Stovall MUS ’04 suggested, “a giant burrito — chicken or beef.” It was a Lincoln arc welder being used for work on heating pipes in a tunnel beneath Cross Campus, said Tim Taylor, the president of the Buckingham Routh Co., the company that performed the job.

Anthony Bonaffini, the manager of distribution for Yale’s utilities department, said the job in the tunnel is complete, so the machine was removed Tuesday.

Taylor said his company was exchanging pressure-reducing stations for the Calhoun heating system located in the tunnel, which runs perpendicular to College Street. The stations convert high-pressure steam to low-pressure steam, which is then used to raise the temperature of the hot water system for the college’s radiators.

Bonaffini said the steam is produced at Yale’s Central Power Plant at Ashmun and Grove streets at 250 pounds per square inch and then immediately brought down to 125 pounds per square inch to be pumped throughout central campus and Science Hill. At stations like the ones at Calhoun, Bonaffini said, the steam is further reduced in pressure for use in buildings.

“It’s steam for the kitchens, your domestic hot water and heating,” Bonaffini said.

After the steam is used, it condenses back to water and is sent back to the power plant, Bonaffini said. He described the immense steam system as being like the body’s circulatory system, with the power plant as its heart and pipes as veins and arteries.

Bonaffini said Buckingham Routh was replacing the valves on Calhoun’s system with newer, more efficient ones. The machine on Cross Campus was being used to weld pipes together.

He said the process had no effect on operations in the college.

“We bypassed it around so they always had heat and water,” Bonaffini said.

Calhoun converted to the steam heating system in 1988, Taylor said.

Bonaffini said workers also performed some regular maintenance on Berkeley’s steam heating system, replacing some valves and flanges.

Students said the machine’s unannounced arrival and departure were “strange.”

“It just appeared one day — and then it disappeared,” Maria Telpoukhovskaia ’07 said.

[ydn-legacy-photo-inline id=”19148″ ]