Scroll expander with back pressure chamber

A scroll expander, comprising:

• a housing;
• and
• an expansion mechanism provided inside the housing and configured to expand a high-pressure fluid with an intake pressure to a low-pressure fluid with an exhaust pressure, the expansion mechanism comprising a fixed scroll and an orbiting scroll and defining therein an exhaust chamber, an intake chamber and a series of closed expansion chambers, wherein a back pressure chamber is provided on the expansion mechanism, and the back pressure chamber is in fluid communication with an intermediate pressure chamber of the series of expansion chambers which has an intermediate pressure lower than the intake pressure and higher than the exhaust pressure,
• wherein at least one passage in fluid communication from the back pressure chamber to a low-pressure zone with the exhaust pressure is provided, and the passage is configured such that the passage is opened when a pressure in the back pressure chamber is less than a pressure in the low-pressure zone and the passage is closed when a pressure in the back pressure chamber is greater than or equal to a pressure in the low-pressure zone.