A pump comprising: a pump body having pump walls substantially cylindrical in shape and having a side wall (11, 15, 18, 22) closed by two end walls (13, 20) for containing a fluid; a disc-shaped actuator disposed between the two end walls (13, 20) and flexibly supported by a ring-shaped isolator, wherein the isolator is supported by the side wall (11, 15, 18, 22) and extends from the periphery of the actuator to the sidewall (11, 15, 18, 22), wherein the actuator and the isolator provide a common end wall forming a first cavity and a second cavity with the end walls, each cavity (16, 23) having a height (h) and a radius (r), wherein a ratio of the radius (r) to the height (h) is greater than about 1.2, the actuator operatively associated with a central portion of the common end wall and adapted to cause an oscillatory motion of the common end wall at a frequency ( f), thereby generating radial pressure oscillations of the fluid within both the first cavity and the second cavity; a first aperture disposed at a location in the end wall associated with the first cavity and extending through the pump wall; a second aperture disposed at another location in the end wall associated with the first cavity and extending through the pump wall; a first valve disposed in one of the first and second apertures (925, 27) to enable the fluid to flow through the first cavity in one direction when in use; a third aperture disposed in the end wall associated with the second cavity and extending through the pump wall; characterised by a second valve disposed in the third aperture to enable the fluid to flow through the second cavity in both directions when in use; wherein the second valve is a dual-valve structure comprising a third valve and a fourth valve arranged to permit airflow in opposite directions; wherein the isolator further comprises a first isolator electrode having: a ring-shaped portion, circumferentially patterned with windows having an arcuate shape that extend around the perimeter of the ring-shaped portion, including an inner ring portion and an outer ring portion which are connected by spoke-members; and a tab portion extending from the outer ring portion. a pump body having pump walls substantially cylindrical in shape and having a side wall (11, 15, 18, 22) closed by two end walls (13, 20) for containing a fluid; a disc-shaped actuator disposed between the two end walls (13, 20) and flexibly supported by a ring-shaped isolator, wherein the isolator is supported by the side wall (11, 15, 18, 22) and extends from the periphery of the actuator to the sidewall (11, 15, 18, 22), wherein the actuator and the isolator provide a common end wall forming a first cavity and a second cavity with the end walls, each cavity (16, 23) having a height (h) and a radius (r), wherein a ratio of the radius (r) to the height (h) is greater than about 1.2, the actuator operatively associated with a central portion of the common end wall and adapted to cause an oscillatory motion of the common end wall at a frequency ( f), thereby generating radial pressure oscillations of the fluid within both the first cavity and the second cavity; a first aperture disposed at a location in the end wall associated with the first cavity and extending through the pump wall; a second aperture disposed at another location in the end wall associated with the first cavity and extending through the pump wall; a first valve disposed in one of the first and second apertures (925, 27) to enable the fluid to flow through the first cavity in one direction when in use; a third aperture disposed in the end wall associated with the second cavity and extending through the pump wall; characterised by a second valve disposed in the third aperture to enable the fluid to flow through the second cavity in both directions when in use; wherein the second valve is a dual-valve structure comprising a third valve and a fourth valve arranged to permit airflow in opposite directions; wherein the isolator further comprises a first isolator electrode having: a ring-shaped portion, circumferentially patterned with windows having an arcuate shape that extend around the perimeter of the ring-shaped portion, including an inner ring portion and an outer ring portion which are connected by spoke-members; and a tab portion extending from the outer ring portion. a ring-shaped portion, circumferentially patterned with windows having an arcuate shape that extend around the perimeter of the ring-shaped portion, including an inner ring portion and an outer ring portion which are connected by spoke-members; and a tab portion extending from the outer ring portion.