Pump efficiency factor analysis and improvement of the pump work volume loss, mechanical loss and hydraulic losses. First, the volume loss: Including through the size of the mouth of the circular flow loss, stuffing box and balance disc leakage loss, stuffing box and balance disc leakage loss within the specified range is a guarantee of normal work loss. The size of the ring mouth of the loss of circulating water flow and size of the main orifice is the size of the gap, length and pump single stage lift related. Under normal circumstances, the length of the seal gap and the pump single-stage head is basically the same, so the size of the mouth ring circulation loss size and size of the main mouth ring gap size, large ring ring sealing gap for each additional 0.2mm, efficiency Lower about 4%; small mouth ring sealing gap for each additional 0.5mm, the efficiency decreased by about 5%. Second, the mechanical loss: refers to the impeller, balance the outer surface of the disc and the water friction, the size of the friction at the mouth ring and bearings and fillers, etc., where the disc friction loss depends on the specific rotation. Loss ratio is higher than the higher loss. Third, water near the mouth of the shaft is rotated water disturbance, so that the inlet angle of water changes resulting in energy loss. The above three in the normal operation of the pump is basically constant. Hydraulic Loss: Hydraulic loss will directly affect the hydraulic efficiency and characteristics of the pump. It includes friction loss, eddy current and impact loss. Under normal circumstances, the greater the flow of the pump less hydraulic loss. Frictional loss is the loss of fluid along the path of impellers and other overcurrent components, and is approximately equal to the square of the flow rate. Eddy current and loss of impact refers to the loss of turning, expansion and contraction of the fluid during the whole flow of the turbine. In the case of the impeller alone, the impact of the fluid on the inlet of the blade and the eddy current loss in the impeller when the flow changes. At rated flow this loss in the impeller is almost zero, and above or below the nominal flow this loss starts to appear and the more the difference to the nominal flow, the greater the loss and the increase in flow squared. This loss of impact distribution is due to less than the rated flow, the fluid impeller angle greater than the impeller installation angle, squeezing the fluid to the blade working surface and the formation of swirl zone on the back; when the flow rate is greater than the rated flow, the fluid and the blade Encounter angle is less than the blade installation angle, the fluid is pressed against the back of the blade, forming a closed eddy current in the face of the accident. This phenomenon has been experimentally confirmed. The hydraulic losses are mainly caused by the hydraulic losses in the segmented multistage pumps with ns (specific rotation) = 90 in the impeller and the flow-through components. The losses in the impellers and other flow-through components are approximately 50%. Impeller blade inlet edge wear, due to changes in the entrance angle will have an unusual entrance impact, the adhesion between the blade runner, reducing the effective flow area, the water flow rate increases, thus increasing the hydraulic loss. When the new impeller, should be as much as possible to clear the glitches in the runner to keep the inner wall smooth, in order to reduce additional hydraulic losses, when conditions permit the use of plastic impeller. Special attention is that when assembling or overhauling the pump, due to the impeller outlet and the aqueduct mismatch or axial channeling amount caused by excessive hydraulic losses, the pump efficiency and characteristics of a greater impact, even if the assembly is correct, this part of the loss Also close to 11%. In addition, the loss of 22% of the runners reversed by the water guide ring to the water return ring eliminates casting defects such as burrs and burrs in the guide vanes to avoid unprofitable hydraulic losses. When each pump is normal, its efficiency will depend on the size of the hydraulic loss. The friction loss in hydraulic loss is inevitable. It is well known that water has the property of sticking. The relative energy per unit volume of water and the surface of the object (overcurrent component), the energy required to maintain its movement and its viscosity, contact area , Surface roughness, the length of the journey along the way, and is proportional to the third power flow velocity. When water flows in the flow channel, the surface water in contact with the flow channel surface will run at a relatively lower speed and cause eddy currents in the water stream to cause energy consumption. The greater the energy loss caused by the relative running speed of the surface water, Therefore, expanding the runner area or reducing the running speed of water flowing in the runner (decreasing the pump shaft speed) can reduce the energy consumption and improve the operation efficiency. The energy required for relative movement between water and water is small and depends essentially on the viscosity of the water. Impact loss and water flow rate are also very much related. When the water flow rate is too high, especially in the vicinity of the impeller suction port, when the water flow to a larger axial velocity impeller suction port, which in turn impetus and rotation Thrown at the radial velocity of the impeller outlet, it can be said that the axial velocity of the kinetic energy in the vicinity of the impeller suction drain depleted. This phenomenon occurs both in the pump primary impeller and in the middle and in the impeller, and the intermediate stage impeller is also more severe than the primary stage impeller because the diameter of the primary stage impeller suction port is generally larger than that of the intermediate stage impeller (in order to improve Water absorption), the first-stage impeller outlet flow outside the axial flow rate can be relatively reduced, and the suction pipe pressure is lower than atmospheric pressure, the first stage impeller thrown water dewatering by the guide ring deceleration, The radial velocity reaches the suction port of the impeller at the intermediate stage. Since the diameter of the suction port is small, the water flow is forced to flow from the radial velocity to the larger axial velocity to the suction port. At this time, the kinetic energy of the water flow in the radial velocity is also Consumed, and the backflow ring of the flow area toward the suction port gradually shrinking, resulting in radial velocity increases, back into the circle of pressure or positive pressure (greater than atmospheric pressure), these cases are not conducive to the loss of water. In general, the hydraulic efficiency of a multistage centrifugal pump with a guide ring increases from a zero flow rate to an increasing flow rate, and at some point, the efficiency decreases. This is because as the flow rate increases, the flow rate of the fluid in the flow-through part increases, greatly increasing the frictional loss, impact loss and eddy-current loss of the flow, resulting in a decrease in efficiency. The new high efficiency water pump has the following features through the special design: The newly designed water pump adopts a new water guide ring to enlarge the flow passage area and reduce the flow rate of water in the overcurrent component. (For example, 150D-30 type pump: The maximum theoretical flow rate at the inlet of the impeller is 4.81m / s at rated condition, the maximum theoretical flow rate in the guide ring is 3.485m / s, while the maximum flow velocity in other pump overcurrent components can reach 15-30m / s, The loss is larger); Adopting the special design of the runner with high efficiency impeller, the flow passage of the impeller can make the water less disturbed and more "free" into the water conducting circle, which can greatly reduce the impact loss of the water flow; Lower flow, enabling head and flow to achieve the best match, so that the pump has a "constant power" feature, the efficiency can reach 90%. Increase the head of the pump to expand the use of the pump, and can save materials, reduce weight and reduce manufacturing costs.
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