PURPOSE:To silence underwater sounds caused by pulsations produced by a plurality of various pumps provided in a submarine through a common silencer by forming the fundamental frequency in the pressure pulsation characteristics of the respective pumps to be an integral magnification of a predetermined frequency. CONSTITUTION:A plurality of pumps 3 each driven by a motor 4 are disposed in a submarine 1. Pipes 5 communicating to a drain port are connected to these pumps 3. Pipes 5 connected to the respective pumps are aggregated into an aggregating pipe 5', and the respective pumps 3 is provided with a common liquid silencer 2. A plurality of pumps 3 and motors 4 for driving them are formed such that the values of fundamental frequences fn of their pressure pulsations are equal to each other or one is the integral magnification of the other. Thus, the underwater sounds on the basis of the pressure pulsations produced by these pumps 3 can be reduced by the common silencer 2.
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