£6.50
Hambleton Bard S30 gas  cylinder - refill

This is the most commonly used refillable CO2 cylinder for topping up the pressure in home beer barrels. Just screw the cylinder down onto the valve to start the gas flowing and turn it back it again to stop. The gas should be added to the keg in short bursts of 1 second to stop the cylinder freezing in the open position. Running the end of the cylinder under hot water after use will also help to prevent this.