The vane pump performance elaboration, are based on the vane pump water conditions meet the requirements as a precondition. Water absorption is to determine the pump installation elevation and into the pool design basis. The controlled self-priming requirement pump cavitation does not occur at any predetermined design operating conditions, to determine the installation height must be met. Pump installation is too low will increase investment in civil engineering pump construction, construction more difficult; too high, the pump cavitation, causing the pump work flow, lift, the efficiency of a substantial decline, or even not work. Therefore, the installation of pumps to determine the elevation is an important issue pumping station design. In the pumping station operation, the pump device failure also has a lot of water from the pump can not meet the requirements. Therefore, the vane pump water absorption, we must attach great importance.
　　
　　 During operation of the water pump , for some reason, the pressure in the local part of the pump drops to the saturated steam pressure (vaporization pressure) of the water at the corresponding temperature, the water begins to vaporize to generate a large number of bubbles which move forward along the water flow and the movement To the site of higher pressure, rapid condensation, collapse. The generation and collapse of bubbles in the water flow inside the pump involve physical and chemical phenomena and generate noise, vibration and erosion of overcurrent components. This phenomenon is called cavitation of the pump.
　　
During the process of cavitation, the regular flow of water flow is destroyed by the inclusion of bubbles in the water flow, which changes the over flow area and the flow direction in the flow channel. As a result, the stability of the energy exchange between the impeller and the water flow is destroyed, and the energy loss Increase, thus causing the pump flow, lift and the rapid decline in efficiency, and even to cut off the state. This change in performance is different for different RPMs. Centrifugal pumps with a low specific rotational speed are narrow and narrow, and are easily obstructed by bubbles. After cavitation occurs, the QH and Q-curve drop rapidly. Centrifugal pumps and mixed flow pumps with medium-to-high specific speed have a gradual decline in the QH and Q-7 curves due to the wide impeller channels and the bubbles are not easily blocked by air bubbles. When the cavitation is severe, it starts to fall sharply. For the axial flow pump with high specific rotation, the QH and Qj curves decrease slowly because the flow path between the blades is quite wide, so the cavitation area is not easy to extend to the entire leaf groove.
　　
When the bubble collapses, the water flows into the center of the bubble due to inertial high velocity, resulting in a strong water hammer with a pressure up to (3.3-570) X107Pa and an impact frequency of 2-300 times / s. Such large pressure frequently acts on Small flow of parts, causing local plastic deformation of the metal surface and hardening brittle, resulting in fatigue phenomenon, the metal surface began to honeycomb, followed by stress is more concentrated, leaf cracks and peeling. This is the mechanical erosion of cavitation.
　　
During the bubble generation in the low pressure zone, the gas dissolved in the water is also precipitated from the water, so the bubble is actually a mixture of water and air. Living gas (such as oxygen) with the condensation of bubbles generated by the high temperature, the metal surface chemical corrosion.
　　
Under high temperature and pressure, the water will produce charged phenomenon. Different parts of the overcurrent components, due to cavitation temperature differences, the formation of thermocouples, resulting in the metal surface electrolysis (ie, electrochemical corrosion).
　　
In addition, when the sediment content in water is high, due to the erosion of sediment, the surface of the overcurrent component of the pump is damaged, and when the cavitation occurs, the damage of the overcurrent component is accelerated.
　　
In the bubble collapse collapse, resulting in instantaneous pressure rise and the impact of the water between the particles and the impact of the flow of components, the pump noise and vibration.
　　
Water absorption performance of the pump, allowing suction on the vacuum height, in order to ensure the lowest pressure pump internal cavitation does not occur, at the pump inlet maximum allowable vacuum, expressed in meters of water column. Any means centrifugal pump and horizontal mixed flow pump water absorption performance of a way. Pump product samples, with Q-Hs curve to represent the water absorption performance of the pump.
　　
Cavitation allowance (NPSH)
　　
Cavitation margin. Refers to the import of the pump, the unit of gravity of water with greater than saturated steam pressure surplus energy, expressed in meters of water column.
　　
Critical cavitation allowance (NPSH) a. Means the lowest point of the pump pressure is saturated steam pressure, the pump inlet cavitation margin. The critical cavitation margin is the critical condition for cavitation in the pump.
　　
Required cavitation allowance (NPSH) r. The cavitation allowance provided in the pump product catalog is the required cavitation allowance. In order to ensure that the normal operation of the sludge screw pump pump does not occur cavitation, the appropriate increase of the critical cavitation margin, which is the necessary cavitation margin. The formula is
　　
(NPSH) r = (NPSH) a + 0.3 m (4-70)
　　
For large pumps, on the one hand (NPSH) a large, on the other hand from the model test to the prototype pump, due to the effect of the proportional effect, 0.3m safety value is too small, (NPSH) r can be calculated using the following formula:
　　
(NPSH) r = (1.1? 1.3) (NPSH) a (4-71)
　　
Allow suction vacuum height and cavitation margin relationship
　　
â‘¡ part of the rotor rotor mainly by the impeller, bushings, sliding bearings, thrust plate, the rotor components such as magnetic components.
　　
â‘¢ connecting part of the connecting part is by the connecting frame, auxiliary bracket, bottom plate and other static connectors, the main support for the connection.
　　
â‘£ transmission part of the transmission part of the pump and the prime mover connection. The connection method is direct connection, making the pump structure more compact.
　　
　　 During operation of the water pump , for some reason, the pressure in the local part of the pump drops to the saturated steam pressure (vaporization pressure) of the water at the corresponding temperature, the water begins to vaporize to generate a large number of bubbles which move forward along the water flow and the movement To the site of higher pressure, rapid condensation, collapse. The generation and collapse of bubbles in the water flow inside the pump involve physical and chemical phenomena and generate noise, vibration and erosion of overcurrent components. This phenomenon is called cavitation of the pump.
　　
During the process of cavitation, the regular flow of water flow is destroyed by the inclusion of bubbles in the water flow, which changes the over flow area and the flow direction in the flow channel. As a result, the stability of the energy exchange between the impeller and the water flow is destroyed, and the energy loss Increase, thus causing the pump flow, lift and the rapid decline in efficiency, and even to cut off the state. This change in performance is different for different RPMs. Centrifugal pumps with a low specific rotational speed are narrow and narrow, and are easily obstructed by bubbles. After cavitation occurs, the QH and Q-curve drop rapidly. Centrifugal pumps and mixed flow pumps with medium-to-high specific speed have a gradual decline in the QH and Q-7 curves due to the wide impeller channels and the bubbles are not easily blocked by air bubbles. When the cavitation is severe, it starts to fall sharply. For the axial flow pump with high specific rotation, the QH and Qj curves decrease slowly because the flow path between the blades is quite wide, so the cavitation area is not easy to extend to the entire leaf groove.
　　
When the bubble collapses, the water flows into the center of the bubble due to inertial high velocity, resulting in a strong water hammer with a pressure up to (3.3-570) X107Pa and an impact frequency of 2-300 times / s. Such large pressure frequently acts on Small flow of parts, causing local plastic deformation of the metal surface and hardening brittle, resulting in fatigue phenomenon, the metal surface began to honeycomb, followed by stress is more concentrated, leaf cracks and peeling. This is the mechanical erosion of cavitation.
　　
During the bubble generation in the low pressure zone, the gas dissolved in the water is also precipitated from the water, so the bubble is actually a mixture of water and air. Living gas (such as oxygen) with the condensation of bubbles generated by the high temperature, the metal surface chemical corrosion.
　　
Under high temperature and pressure, the water will produce charged phenomenon. Different parts of the overcurrent components, due to cavitation temperature differences, the formation of thermocouples, resulting in the metal surface electrolysis (ie, electrochemical corrosion).
　　
In addition, when the sediment content in water is high, due to the erosion of sediment, the surface of the overcurrent component of the pump is damaged, and when the cavitation occurs, the damage of the overcurrent component is accelerated.
　　
In the bubble collapse collapse, resulting in instantaneous pressure rise and the impact of the water between the particles and the impact of the flow of components, the pump noise and vibration.
　　
Water absorption performance of the pump, allowing suction on the vacuum height, in order to ensure the lowest pressure pump internal cavitation does not occur, at the pump inlet maximum allowable vacuum, expressed in meters of water column. Any means centrifugal pump and horizontal mixed flow pump water absorption performance of a way. Pump product samples, with Q-Hs curve to represent the water absorption performance of the pump.
　　
Cavitation allowance (NPSH)
　　
Cavitation margin. Refers to the import of the pump, the unit of gravity of water with greater than saturated steam pressure surplus energy, expressed in meters of water column.
　　
Critical cavitation allowance (NPSH) a. Means the lowest point of the pump pressure is saturated steam pressure, the pump inlet cavitation margin. The critical cavitation margin is the critical condition for cavitation in the pump.
　　
Required cavitation allowance (NPSH) r. The cavitation allowance provided in the pump product catalog is the required cavitation allowance. In order to ensure that the normal operation of the sludge screw pump pump does not occur cavitation, the appropriate increase of the critical cavitation margin, which is the necessary cavitation margin. The formula is
　　
(NPSH) r = (NPSH) a + 0.3 m (4-70)
　　
For large pumps, on the one hand (NPSH) a large, on the other hand from the model test to the prototype pump, due to the effect of the proportional effect, 0.3m safety value is too small, (NPSH) r can be calculated using the following formula:
　　
(NPSH) r = (1.1? 1.3) (NPSH) a (4-71)
　　
Allow suction vacuum height and cavitation margin relationship
　　
â‘¡ part of the rotor rotor mainly by the impeller, bushings, sliding bearings, thrust plate, the rotor components such as magnetic components.
　　
â‘¢ connecting part of the connecting part is by the connecting frame, auxiliary bracket, bottom plate and other static connectors, the main support for the connection.
　　
â‘£ transmission part of the transmission part of the pump and the prime mover connection. The connection method is direct connection, making the pump structure more compact.
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