Abstract: A valve comprising a first chamber (111) and a second chamber (112), wherein a movable member (204) is arranged to selectably bring the first and second chambers into and out of fluid communication with one another, the movable member arranged such that when in an open position wherein the first and second chambers are in fluid communication, gas at a first pressure in the first chamber provides a closing force to a first surface area (222) of the movable member to overcome an opening force provided by gas at a second pressure in the second chamber on a second surface area (223) of the movable member whereby the movable member moves to a closed position to isolate the first and second chambers, and further arranged wherein as the movable member moves to the closed position, the second surface area of the movable member exposed within the second chamber is reduced thus reducing the opening force provided by the gas at the second pressure and providing a bias towards the closed position.

Abstract: A valve comprising a first chamber (111) and a second chamber (112), wherein a movable member (204) is arranged to selectably bring the first and second chambers into and out of fluid communication with one another, the movable member arranged such that when in an open position wherein the first and second chambers are in fluid communication, gas at a first pressure in the first chamber provides a closing force to a first surface area (222) of the movable member to overcome an opening force provided by gas at a second pressure in the second chamber on a second surface area (223) of the movable member whereby the movable member moves to a closed position to isolate the first and second chambers, and further arranged wherein as the movable member moves to the closed position, the second surface area of the movable member exposed within the second chamber is reduced thus reducing the opening force provided by the gas at the second pressure and providing a bias towards the closed position.