Broken spring valve

An AVK non-return valve with a broken spring.

Broken spring

Operating spring

Top plot: Vibration RMS value, for a cyclic on-off pump operation.
Bottom plot: Vibration Crest Factor plotted, with faulty non-return valve (broken spring) until 14:40 and repaired valve with a new spring after 14:40.

The spring tension ensures fast and gentle closing which prevents water hammer. If a pump stops and the forward flow reverses back down the line towards the pump before the check valve has fully closed, the flow will force the valve door to slam onto its seat and will almost instantaneously stop the reverse flow resulting in pipeline water hammer and producing hammer noises.

This can be monitored with the Crest factor. The Crest factor is a dimensionless ratio-based parameter used to characterize a waveform, defining the ratio between the Peak values (either positive or negative) of a waveform to its RMS value, and it is a measure of how far the waveform deviates from its average value.