A dual pressure respiratory assistance device including a gas source which supplies a flow of gas into an air tube having a bubbler branch and a patient branch. A first tube that is connected to the bubbler branch is at least partially submerged in a fluid. An oscillatory relief valve cycles between first and second configurations. The relief valve includes an oscillating member which captures gas released through at least one hole in the first tube when the oscillating member is in a first position. The gas in the oscillating member causes the oscillating member to rise to a second position, wherein gas is released from the oscillating member and the at least one hole is blocked when the oscillating member reaches the second position.