A hermetic vessel capable of preventing noise caused by fluid flow, and an oil separator, a gas-liquid separator, and an air conditioning system using the same. The hermetic vessel having a vessel body includes an inlet through which a fluid flows into the vessel body, and a discharge pipe which is inserted into the vessel body to discharge the fluid. The discharge pipe includes a first discharge pipe which guides a flow of the fluid in a first direction and causes a wave of a higher frequency than an audible frequency, and a second discharge pipe which is connected to the first discharge pipe to guide a flow of the fluid from the first discharge pipe in a second direction which is different from the first direction.