An apparatus can include a piston movably disposed within a pressure vessel and defines a first interior region and a second interior region. The piston has a first position in which the first interior contains a gas having a first pressure and has a volume greater than the second interior region, and a second position in which the second interior region contains a gas having a second pressure and has a volume greater than the first interior region. A seal member is attached to the piston and to the pressure vessel. The seal member has a first configuration in which at least a portion of the seal member is disposed at a first position when the piston is in its first position, and a second configuration in which the portion of the seal member is disposed at a second position when the piston is in its second position.
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