Russia shut off the flow of natural gas into Ukraine on Wednesday, according to an announcement from the national gas company, Gazprom. How do you turn off the gas to an entire country?
Switch off valves in the pipeline or shut down the compressor stations. Gas pipelines typically have valves spaced out every several miles, enabling gas to be shut off if necessary. In addition to regulating how much gas is being delivered downstream, the valves are there for safety purposes, enabling pipeline operators to stop the flow of gas immediately if there is a leak, for example. The valves also allow operators to shut down a section of the pipeline when it needs maintenance. Depending on the pipeline, a valve might be closed manually, or operators may be able to push a button that mechanically shuts the valve. (A massive explosion along a New Jersey gas pipeline in 1994, which occurred when pipeline operators couldn't reach a manually operated valve, spurred a call for more remote-control valves in the United States.)
But it's not just the valves that can slow the flow of gas along the pipeline—and that's part of the reason the dispute over Gazprom has been so tense. Transporting natural gas over long distances requires pressurizing it. Due to friction, however, the gas loses some of that pressure as it moves downstream. As a result, compressor stations are necessary to repressurize the gas and keep it moving forward. To accomplish this, the stations use turbines that are powered by the gas. In large U.S. pipelines, compressor stations are placed between 50 and 100 miles apart from each other.
Some of the compressor stations needed to get Gazprom's deliveries to Europe are on Ukrainian soil, and the company has accused the locals of siphoning off gas that's bound for Europe. (The same pipeline is used to carry gas for both Ukrainian and European customers.) Gazprom further claims that these Ukrainian compressor stations had already been shut off before Wednesday—which would have kept any European-bound gas in Ukraine—and that's what led Russia to stop its supply. Ukraine says that the gas Russia accuses it of siphoning was actually "technical gas" needed to power the compressor stations' turbines. The key sticking point between the two sides now appears to be the makeup of an outside team that would monitor what happens to the gas within the Ukrainian portion of the pipeline.
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Explainer thanks Tom Miesner of Pipeline Knowledge and Development, Jonathan Stern of the Oxford Institute for Energy Studies, and Brian Towler of the University of Wyoming.