A pressure vessel refuelling system enables reduced recompression heating in vehicle CNG pressure vessels during refuelling. The system includes a first pressure vessel and a second pressure vessel, each vessel having at least one opening for the entry and exit of a gas and a liquid. A liquid line establishes fluid communication between the first and second pressure vessels via the at least one opening in each of the first and second pressure vessels. A backpressure control device is operatively connected to the liquid line, whereby during refuelling of the first pressure vessel a gaseous fuel from a refuelling station flows into the first pressure vessel, and whereby a liquid in the first pressure vessel flows, under control of the backpressure control device, from the first pressure vessel through the liquid line to maintain a near constant pressure in the first pressure vessel.