A disc pump (10, 110, 210) comprising: a pump body having a cylindrical sidewall closed at both ends by a first end wall (20, 120) and a driven end wall (22, 122) to form a cavity (16, 116) for containing a fluid; an actuator (30, 130, 230) formed from a flexible membrane adapted to hold an electrostatic charge and operatively associated with the driven end wall (22, 122) to cause an oscillatory motion of the driven end wall (22, 122) at a drive frequency, thereby generating displacement oscillations of the driven end wall (22, 122) in a direction perpendicular thereto; a first conductive plate (40, 140, 240) positioned to face the actuator (30, 130, 230) outside of the cavity (16, 116) and adapted to provide an electric field of reversible polarity, the first conductive plate (40, 140, 240) being electrically associated with the actuator (30, 130, 230) to cause the actuator (30, 130, 230) to oscillate at the drive frequency in response to reversing the polarity of the electric field; a second conductive plate (141, 241) positioned on an opposite side of the actuator (30, 130, 230) from the first conductive plate (40, 140, 240), the second conductive plate (141, 241) adapted to provide an electric field of reversible polarity and electrically associated with the actuator (30, 130, 230) to cause the actuator (30, 130, 230) to oscillate at the drive frequency in response to reversing the polarity of the electric field of the second conductive plate (141, 241), wherein the electric field of the second conductive plate (141, 241) is adapted to have an opposite polarity to the electric field of the first conductive plate (40, 140, 240); a first aperture (27, 127) disposed at any location in the first end wall (20, 120) and extending through the pump body; a second aperture (31, 131) disposed at any location in the pump body other than the location of the first aperture (27, 127) and extending through the pump body; and a valve (29, 60, 129) disposed in at least one of the first aperture (27, 127) and the second aperture (31, 131); whereby the displacement oscillations generate corresponding pressure oscillations of the fluid within the cavity (16, 116) causing fluid flow through the first aperture (27, 127) and the second aperture (31, 131) when in use. a pump body having a cylindrical sidewall closed at both ends by a first end wall (20, 120) and a driven end wall (22, 122) to form a cavity (16, 116) for containing a fluid; an actuator (30, 130, 230) formed from a flexible membrane adapted to hold an electrostatic charge and operatively associated with the driven end wall (22, 122) to cause an oscillatory motion of the driven end wall (22, 122) at a drive frequency, thereby generating displacement oscillations of the driven end wall (22, 122) in a direction perpendicular thereto; a first conductive plate (40, 140, 240) positioned to face the actuator (30, 130, 230) outside of the cavity (16, 116) and adapted to provide an electric field of reversible polarity, the first conductive plate (40, 140, 240) being electrically associated with the actuator (30, 130, 230) to cause the actuator (30, 130, 230) to oscillate at the drive frequency in response to reversing the polarity of the electric field; a second conductive plate (141, 241) positioned on an opposite side of the actuator (30, 130, 230) from the first conductive plate (40, 140, 240), the second conductive plate (141, 241) adapted to provide an electric field of reversible polarity and electrically associated with the actuator (30, 130, 230) to cause the actuator (30, 130, 230) to oscillate at the drive frequency in response to reversing the polarity of the electric field of the second conductive plate (141, 241), wherein the electric field of the second conductive plate (141, 241) is adapted to have an opposite polarity to the electric field of the first conductive plate (40, 140, 240); a first aperture (27, 127) disposed at any location in the first end wall (20, 120) and extending through the pump body; a second aperture (31, 131) disposed at any location in the pump body other than the location of the first aperture (27, 127) and extending through the pump body; and a valve (29, 60, 129) disposed in at least one of the first aperture (27, 127) and the second aperture (31, 131); whereby the displacement oscillations generate corresponding pressure oscillations of the fluid within the cavity (16, 116) causing fluid flow through the first aperture (27, 127) and the second aperture (31, 131) when in use.