Formation and harm of axial force
When the heat conduction oil pump impeller (except double suction impeller) works, the liquid enters the impeller at low pressure P1 and flows out of the impeller at high pressure P2. Moreover, the asymmetric shape of the front and rear cover plates of the impeller makes the liquid pressure on both sides of the impeller unequal, resulting in the axial thrust. Liquid pressure distribution on both sides of impeller.
Due to the uneven force on both sides of the impeller, the centrifugal pump in operation, the formation of an axial and pointing to the impeller entrance, while acting on the rotor force, this force makes the whole rotor pump to the impeller suction end of the movement, causing the vibration of the pump, bearing heating, and even damage parts, so that the pump can not work normally. Especially multistage pump, the influence of axial force is more serious.
2) Balance of axial force
When the impeller of heat conduction oil pump produces large axial force, and all act on the bearing, the bearing is difficult to bear. Therefore, balance measures must be taken to eliminate or reduce the axial force to ensure the safe operation of centrifugal pump.
(1) Single stage centrifugal pump axial force balance method:
(1) on the impeller opening balance hole the purpose is to make the pressure on both sides of the impeller are equal, so that the axial force balance shown in (a), on the impeller wheel near the wheel yi symmetrically drill a few holes (called balance hole), and on the pump casing and the wheel radius r, set sealing ring, reduce pressure difference on both sides of impeller liquid greatly, reduce the axial force effect. This method is simple and reliable, but some liquid reflux impeller suction, reduce the efficiency of the pump. This method is widely used in single stage single suction centrifugal pump.
(2) The use of double suction impeller it is the use of impeller itself structural characteristics, to achieve their own balance, due to double suction impeller symmetrical on both sides, so in theory will not produce axial force, but because of the manufacturing quality and impeller on both sides of the liquid flow difference, it is impossible to make the axial force completely balanced.
(3) t radial rib plate is set on the impeller on the outside of the impeller wheel set radial reinforcement plate to balance the axial force, set in the radial steel plate, the impeller by radial rib plate, liquid in the high side at nearly the speed of the impeller rotating speed rotation, in under the action of centrifugal force, reduce the liquid in the cavity pressure, axial force balance on both sides so that the impeller. The disadvantage is the additional power loss. Generally, 4 radial ribs are used in small pumps, and 6 radial ribs are used in large pumps.
(4) when the above method can not completely eliminate the axial force, the method of installing thrust bearings should be used to bear the remaining axial force.
