Reference Manual

6−10

Control Valve Noise Summary

The requirement for noise control is a function of

legislation to protect our wellbeing and to prevent

physical damage to control valves and piping.

Noise prediction is a well defined science. Actual

results will be within 5 dBA of predicted levels.

Prediction is based upon contributions for:

D Pressure drop

D Flow rate

D P/P

and trim style

D Piping and insulation

D Downstream pressure

Noise reduction is accomplished in two general

ways:

1. Source treatment, which acts upon the amount

of noise generated

2. Path treatment, which blocks transmission on

noise to the environment.

There are two common source treatments:

1. Valve noise trim is based on principles of

dividing the flow to create many small noise

sources which combine to a lower level than a

single large flow noise. Diffusers used with control

valves share pressure drop creating two lower

noise sources which again combine to an overall

lower level.

2. Path treatment involves use of insulation or

absorptive devices to lower the sound level which

reaches observers.

Hydrodynamic noise from liquid flow streams can

mainly be traced to cavitation. In this case,

damage from the cavitation is of more concern

than the noise. Appropriate treatment of the

cavitation source should be initiated through

staging the pressure drop.

Two-phase, or pure flashing, applications do not

create noise problems, and there is no technically

appropriate two-phase noise prediction method.