Centrifugal pump volume loss seal ring leakage loss, balance leakage and interstage leakage loss. First, the seal ring leakage loss In the impeller at the entrance, with a seal ring, the pump work, due to the pressure difference exists on both sides of the seal ring, the impeller exit side of the approximate pressure, one side of the impeller inlet pressure, so there will always be A portion of the liquid leaks from the impeller exit toward the impeller inlet. This part of the liquid in the impeller to get the energy, but the liquid is not sent, thus reducing the pump water supply. The energy of the leaked liquid is all used to overcome the resistance of the seal ring. Obviously, the larger the seal ring diameter Dw, the greater the difference between the two sides of the pressure difference, the greater the amount of leakage. For the shape of the pump, in order to reduce the leakage to improve the efficiency of the pump, the seal ring clearance should be allowed to narrow. In general, the total clearance is taken as 0.002 of the diameter of the seal ring. If Dw = 200 mm, the total clearance is 0.40 mm. Assembly, the seal ring can not be too eccentric, otherwise, the leakage will increase. In addition, the method of increasing the resistance of the seal ring can reduce the amount of leakage and the main measure for increasing the resistance is to make the seal ring into a labyrinth, zigzag and the like, which also increases the seal length of the seal ring and increases the resistance along the route. Leakage of the seal ring, which in some cases can cause turbulence at the impeller inlet, makes it necessary to design the seal ring rationally. Second, the balance leakage leakage mechanism In many centrifugal pumps, are equipped with a balance of axial thrust of the body: such as the balance hole, balance pipe, balance disc and so on. Due to the pressure differential on both sides of the balance mechanism, some of the liquid also leaks from the high pressure area to the low pressure area. Leakage of the balance hole will reduce the pump efficiency by about 5%. In the balance disc mechanism, the amount of leakage accounts for 3% of the work flow, but the high-pressure pump is somewhat larger than this value. To reduce the leakage loss, the balance disc diameter D 'can be reduced without affecting the balance force. Third, the interstage leakage loss In the multi-stage pump in the volute, inter-level partition pressure on both sides, and therefore there is leakage loss, according to the different institutional arrangements, the level of partition on both sides of the pressure may be a level, Two or three, the more the difference between the series, the more serious leakage between the separator level, so here widely used step interstage seal. In addition, interstage multistage pumps, there are also interstage leakage. However, this is not the same as the leakage between the different levels, because this part of the liquid leakage through the impeller, it does not belong to the volume loss. Here, the pressure difference before and after the inter-stage partition is caused by the supercharging effect of the diffusion part of the guide vane and the suction effect of the impeller backlash (equivalent to the centrifugal impeller). Under the action of pressure difference, the leaking liquid enters the clearance of the front impeller along the interstitial partition gap and flows back to the interstage gap through guide vanes and anti-guide vanes (sucking guide vanes), repeating the above process. Although the inter-stage leakage of a segmented multistage pump is not a loss of capacity, it flows back and forth in such a way that it consumes the power of the pump. In addition, passage of the part of the liquid through the guide vanes causes a reduction in the effective cross-section of the guide vane throat (ie, leakage of liquid takes up a part of the cross-section), thereby increasing the flow rate there and causing additional hydraulic losses. According to "Centrifugal Pump Design Basics," a book description: A multi-stage pump, the flow rate of 20 liters / sec, the interstage gap reduced from 0.75 mm to 0.25 mm, interstage leakage q reduced 0.7 liters / sec , Due to the decrease of q, the flow through the vane is reduced, the flow velocity of the vane in the vane is reduced, the hydraulic loss in the vane is reduced, meanwhile, the relative velocity of the liquid in the vane wheel and the guide vane backlash Reduced, thus reducing the impeller disc friction loss, so the pump efficiency increased by about 5%.