Abstract: An air actuated seismic signal generator, commonly termed an air gun includes a cylindrical casing that is divided into a control chamber and a firing chamber by a sliding valve. The end face of the sliding valve that is exposed to the control chamber has a greater area than the end face exposed to the firing chamber. An air exhaust port is provided in the firing chamber; the exhaust port may be opened or closed by sliding the valve away from or towards a seat that is associated with the exhaust port. Air is admitted to the control chamber at a relatively low pressure of about 500 psi, and holds the valve in the exhaust-port-closed position because of the differential forces on the valve end faces. The firing chamber is pressurized to a relatively high pressure of about 5000 psi by a separate air supply. There is no air communication or equalization between control and firing chambers.