Standpipes used to attenuate Standing waves

The standpipe can be used when there is a standing wave setup in pipework system.
The standpipe length plus an end correction will attenuate a frequency with and equivalent 1/4 wavelength.

The standpipe also has the benefit of attenuating the fundamental and all of the odd harmonic frequencies.
This device is very useful when a single constant tone is generated. i.e. when a pump is operating at a fixed speed.