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How do parade organizers get 700,000 cubic feet of helium to New York City?

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Workers at an industrial gas facility in Bethlehem, Pennsylvania, store a mix of gaseous and liquid helium in large cryovessels, which have five layers of antimagnetized steel or aluminum. Liquid nitrogen between the outermost layers and an airless vacuum between the rest maintain the helium at or near minus 452.2 degrees Fahrenheit. Over time more of the liquid helium in the tanks turns to gas, but the temperature remains the same.

A few days before the parade, workers connect a cryovessel to a helium compressor. A piston in the compressor then creates suction, pulling the gaseous helium into a compression chamber through a hinged flap. As the flap closes, the piston reverses, compressing the gas and opening a second hinged flap that rushes now-compressed—but still gaseous—helium through a manifold and into a large tube trailer, of up to 180,000 cubic feet, for transport.

Four tube trailers filled to 3,000 pounds per square inch roll into Manhattan the day before Thanksgiving. Dozens of volunteers fill each four-story-tall balloon through a hose that attaches to the tubes on the trucks. The compressed helium's intense pressure would rush out too fast for workers to control, but a pressure-reducing valve limits flow to a safe 50 psi.

After the parade the balloons vent the helium into the atmosphere.

This story appears in the November 2015 issue of Popular Mechanics