It was discussed earlier how large pressure drops across valves induce considerable noise. Figure 2.87 shows how the proportion of energy loss converted to noise (acoustic efficiency) increases with the size in pressure drop.
This effect is reduced dramatically by using valves that employ adiabatic flow with friction, as discussed earlier. Noise can be reduced further by increasing the thickness of the downstream piping and covering it with acoustic insulation. Figure 2.88 shows the ratios of pipe thickness to pipe length used to create further noise attenuation. Even more attenuation is achieved on the control valves that exit to atmosphere (Bank 3 on nuclear plant) by including a silencer.