Seismic source

DETAILED DESCRIPTION We claim: 1.
A water gun seismic source for emitting jets of water into an underwater environment to generate seismic signals comprising a housing having a jet aperture with at least one jet aperture port, means defining a chamber in said housing in which said jet aperture port is located and for providing pressurized water in said chamber, a movable valve disposed in porting relationship with said jet aperture port and having an actuating surface and a sealing surface which face in opposite directions, said housing being provided with a seating surface on which said sealing surface seats to close the jet aperture port, means for applying a relatively constant pressure against said actuating surface to develop a force for moving said valve sealing surface against said seating surface to close said aperture port, and means communicating with said seating surface for applying upon command a pressure to said sealing surface for developing a force thereon greater than the force applied against said actuating surface for moving said valve away from said seating surface for opening said jet aperture port whereby to emit a jet of water.
2.
The source according to claim 1 wherein the pressurized water providing means comprises a reciprocal drive piston which separates said chamber and a region in said housing for containing compressible fluid, means for moving said piston towards said region when said jet aperture port is closed and for providing compressed fluid in said region thereby to pressure the water in said chamber and to cock said water gun, said piston being movable in a direction away from said region under the pressure of the compressed fluid therein into porting relationship with said jet aperture, after said valve opens said jet aperture port, to close said aperture port to terminate the jet.
3.
The source according to claim 2 wherein said housing has a bore in which said drive piston is reciprocally mounted, said bore defining said chamber and having a section of smaller diameter in which said jet aperture is disposed, said bore having a section of larger diameter spaced in the direction of said region from said section of smaller diameter and in which said piston is reciprocal, said bore section of small diameter defining a passage for higher velocity of flow of water through said jet aperture than the velocity of flow in said bore section of larger diameter when said jet aperture opens