Mathematical Determination of Leakage past Turbine and Pump Wearing Rings and Procedure for Designing Serrated Rings

摘要

Clearance between stationary and rotating parts of turbines and pumps is necessary to prevent metal-to-metal contact with resulting possible seizure. This clearance is usually provided by replaceable wearing rings located between the high- and low-pressure areas outside the water passages. Clearance will increase due to wear, causing more leakage through the rings. Since this increase in leakage represents a decrease in efficiency and capacity, there comes a time when it will be economical to restore the original clearance. Economics of the restoration work may hinge on a small decrease in efficiency and capacity. Results of index testing have not proven sufficiently reliable or consistently accurate to detect such small quantities. A mathematical approach is outlined by which increase in leakage through the rings of turbines or pumps may be determined. A curve is shown which relates ring clearance and width to differential head and leakage per foot of ring diameter for plain rings. The mathematical approach, being more reliable and consistent than index testing, provides a means of determining clearance at which restoration work will be economically feasible. Tests at Tracy Pumping Plant verify computed results showing a reduction of 10 to 15% in leakage through a given ring clearance with serrated rings in place of plain rings. Includes a procedure for designing serrated rings. (Author)