the pressure surrounding each bladder 12 or 13 as fluid 24 enters an embodiment having a single device 10 it flows into the first bladder 12 in order for bubble formation and appreciable energy storage to occur the inside of the bladder 12 needs to see some pressure p expan greater than that which the outside of the bladder 12 is seeing in an alternate embodiment having a series of devices 10 as best seen in fig1 a the outside of the first bladder 12 in the series is surrounded by working fluid 24 which is in direct contact with the inside of a second bladder 13 since the working fluid 24 and the bladders 12 and 13 are incompressible for the first bladder 12 to expand it needs to force the working fluid 24 into the second bladder 13 the outside of which is subjected to working fluid 24 at atmospheric pressure the second bladder 13 in turn also needs to see a pressure difference of p expan for bubble formation and subsequent energy storage to occur thus the inside of the second bladder 13 in the series will need to reach a pressure of to initiate energy storage through bubble propagation in turn for the first bladder 12 in the configuration to do the same its inside.