Cavitation indices for pumps in the Irtysh-Karaganda canal

Conclusions

• 1. Cavitation on the walls of the internal passages of the OP10-185 and OP11-185 pumps occurs only on the impeller and at the leading edges of the guide vanes. The extent of the cavitation zones increases with increasing deflection angles of the blades and head of water and with decreasing degree of partial submergence of the impeller.

• 2. With partial submergence of the impeller of the OP11-185 pump of less than 3 m, and of the impeller of the OP10-185 pump of less than 4m, it is undesirable to operate with blade angles exceeding −2°, and it is convenient to use a larger number of pumps with a smaller blade defelection angle.

• 3. At newly designed pumping plants, the partial submergence of the impeller should be established as not less than 4.5 m for OP10-185 pumps, and as not less than 3 m for OP11-185 pumps.

• 4. The significant increase in the extent of the cavitation zones and decrease in the efficiency with an open or loosely closed vacuum valve in the siphon indicate the need for careful regulation of the valve and the inadmissibility pump operation with open valves in siphon outlets.

• 5. As a result of wide variations in the operating regimens of the OP10-185 and OP11-185 pumps installed at the plants on the Irtysh-Karaganda canal, practically all these pumps operate periodically under cavitation conditions. Hence, for such conditions it is justifiable to use pumps with impellers and casings fabricated from cavitation-resistant stainless steel.

• 6. In order to improve the cavitation indices of the pumps and to reduce the wear of the impeller blades, equal angles of setting of the blades should be ensured.

• 7. During stopping of the OP11-185 pump, cavitation is observed at the trailing (upper) edges as viewed from the operating side of the blades. The pressure pulsations in the impeller casing reach 5H_st. Cavitation and pressure pulsations were less significant in the OP10-185 pump during its stopping.