Interpretable Valve Impact Phase Diagnostic Indicator and Its Application in Fluid-End Fault Detection of a Five-Cylinder Drilling Pump

The drilling pump is a critical piece of equipment widely used in oil and gas drilling. During operation, the fluid end generates periodic impact vibration signals due to the opening and closing of valves. When faults such as sealing degradation occur in the fluid end, abnormal fluctuations in cylinder pressure arise, subsequently causing deviations in the valve closing phase from its normal range. Based on this physical mechanism, this study investigates the causal relationship between cylinder pressure disturbances and valve closing phase, and proposes a diagnostic indicator based on the distribution characteristics of discharge valve closing phases across cylinders. This indicator quantifies intercylinder phase differences and fluctuation amplitudes. On this basis, an anomaly detection method is developed by fusing eddy current displacement signals and vibration signals. Specifically, the method extracts discharge valve closing events through signal fusion, obtains the closing phase for each cylinder, and constructs phase variance and mean metrics to characterize the distribution. A support vector machine is then employed to classify normal and faulty states. Validation on a five-cylinder drilling pump test platform shows that the proposed method achieves a fault detection accuracy exceeding 93% under various fault conditions, with over 15% improvement in Accuracy, Precision, and F1-score compared to traditional vibration-based indicators. The results demonstrate that the proposed approach offers strong fault interpretability, high detection accuracy, and practical applicability, providing an efficient and reliable technique for identifying abnormal conditions in the fluid end.