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Determination of cavitation boundary value
Liquid ring vacuum pumps available on the market can generally be categorized into two main types based on their design operating range: those designed for 1013 to 160 mbar (a) and those designed for 1013 to 33 mbar (a). If you're interested in other pump types, you might also find Magnetic Pumps, High-Temperature Magnetic Pumps, Stainless Steel Magnetic Pumps, Pipeline Pumps, Vertical and Horizontal Pipeline Pumps, Pneumatic Diaphragm Pumps, and Electric Diaphragm Pumps of interest. Welcome to Shanghai Xie Jin Pump Co., Ltd.
Pumps designed for the 1013–160 mbar (a) range are typically used in applications where vacuum requirements are not too strict. When operating with water at room temperature, these pumps have a larger limit operating point compared to the corresponding saturated vapor pressure, making cavitation less likely. However, it's recommended that the minimum working pressure should not drop below 160 mbar (a).
On the other hand, pumps designed for the 1013–33 mbar (a) range often operate closer to the saturated vapor pressure of the working fluid, which can lead to varying degrees of cavitation. For example, when the water temperature is 35°C, the corresponding saturated vapor pressure is 56.223 mbar (a). Even though the pump is designed for a range down to 33 mbar (a), it may not actually reach that level. At 56.223 mbar (a), boiling can occur on the inner surface of the suction ring.
Most liquid ring vacuum pumps use water as the working fluid, with international standards set at 15°C or 20°C. Under these conditions, the pump’s performance is tested and considered standard. However, if the water temperature deviates from these standards, the pump’s suction performance can be significantly affected.
Figure 2-93 shows the correction curve for vacuum pump suction performance under different water temperatures. Based on test runs and cavitation occurrences, the critical point for cavitation is generally determined by the saturation vapor pressure plus a Δ value. These points form what is known as the cavitation boundary line.
For pumps designed to operate at a limit of 33 mbar (a), when the water temperature ranges from 10°C to 45°C, the Δ value is typically between 24 and 10 mbar, based on test data. If other liquids are used as the working fluid, the same method can be applied to determine the cavitation threshold. This ensures optimal performance and avoids damage caused by cavitation.