Abstract: Aiming at the extraction of failure character signal for liquid valve, a novel method to combine undecimated lifting scheme packet (ULSP) with singular value decomposition (SVD) is developed. Initial operators are calculated by using Lagrange interpolation formula after determining decomposition level and the lengths of initial operators, and then the original signal is decomposed by using undecimated algorithm. All frequency bands signals of the last layer are denoised by using SVD thresholding, a reasonable order for noise reduction is selected according to the singular entropy of singular spectrum. Then signal is reconstructed by using reconstruction algorithm, and the denoised signal is decomposed by using ULSP again in order to extract fault feature. Simulative signal and engineering results confirm the better noise reduction of ULSP-SVD. The weak fault signal of the spring on the drain valve of a reciprocating water-flood pump is extracted from the strong vibration background.

Key words: Fault diagnosis, Liquid valve, Singular value decomposition, Undecimated lifting scheme packet