Recently, the multi-stage boiler feed pump manufacturer "Changsha Zhonglian Pump Industry" received an order from a customer for the repair of the balance plate of the multi-stage boiler feed pump. Fault handling, next follow me to understand the multi-stage boiler feed pump horizontal multistage centrifugal pump balance plate wear serious reasons。
The multi-stage boiler feed pump equipped with 50MW generator set of the customer company is DG280-95*6 multi-stage boiler feed pump produced by Shenyang Water Pump Factory, with flow rate of 280m³/h, head of 524m and speed of 2980r/min. The multi-stage boiler feed pump balance mechanism adopts balance disk plus thrust bearing (thrust tile) to balance the axial thrust, which often occurs during operation because the balance force cannot balance the axial thrust. Balance axial thrust, resulting in thrust tile burned, balance plate and balance seat serious wear events, and cause multi-stage boiler feed pump violent vibration, especially in the small flow, often due to increased vibration and multi-stage boiler feed pump forced out of operation.
Multi-stage boiler feed pump balance plate failure cause analysis
In order to reduce the magnitude of the balance disk movement, there must be a large dynamic recovery force to restore the balance as soon as the rotor leaves the balance position. To increase the dynamic restoring force, the instantaneous balancing force must be increased, and this is achieved by increasing the differential pressure between the two sides of the balancing disc P2 . In other words, the greater the P2 , the greater the dynamic restoring force and the more quickly the equilibrium position can be restored once the balance disc has left the equilibrium position. So, how can P2 be increased Only if P4 becomes larger (since P2 =P4 -P5 and P5 remains almost constant), and this can only be achieved if the flow pressure drop P1 across the gap a is significantly reduced by the leakage volume. The flicking of the balance disc does not affect the flow in this gap, and the leakage q depends on the radial gap a.
At a certain gap a, the flow pressure drop P1 is proportional to the square of the leakage q. When the balance disc is leftwardly displaced, the leakage volume decreases with the reduction of the clearance b. If the total pressure drop across the radial clearance a and axial clearance b remains the same, i.e. P = P1 + P2 , then the flow pressure drop decreases a lot, which will inevitably increase the pressure difference between the two sides of the balance disc P2 by a lot, while the increase in P2 , i.e. the increase in dynamic recovery force, will prompt the balance disc to return to the equilibrium position.
So the question is how to make the flow pressure drop P1 significantly smaller under dynamics, which obviously can only be achieved if the flow pressure drop P1 is a larger part of the total pressure drop at rest. For example, suppose that the total pressure drop P = 100 kg/cm2 , where P1 = 90 kg/cm2 and P2 = 10 kg/cm2 , when q is reduced by half, P1 decreases from 90 kg/cm2 to 22.5 kg/cm2 , so that P2 = 100-22.5 = 77.5 kg/cm2 and the instantaneous equilibrium force is 7.75 times the original equilibrium force, i.e. the dynamic recovery force increases to 7.75 times the original This means that the dynamic recovery force increases to 7.75 times the original balancing force, thus allowing the balance disc to quickly return to its equilibrium position. However, the pressure drop against the front radial clearance P1 must not be too large, as this will result in too little pressure drop across the second axial clearance and insufficient balancing force, which will eventually lead to the need to increase the diameter of the balancing disc to increase the static balancing force.
The increase in the diameter of the balancing disc is limited by the equipment, and often because the perpendicularity between the plane of the balancing disc and the axis is difficult to reach a smaller permissible value, thus making the second axial clearance b larger, reducing the pressure difference between the two sides of the balancing disc and making the balancing force smaller. Conversely, if where P1 = 10 kg/cm2 and P2 = 90 kg/cm2 , when q is reduced by half, P2 decreases from 10 kg/cm2 to 2.5 kg/cm2 , so P2 = 100-2.5 = 97.5 kg/cm2 , the instantaneous dynamic balancing force only increases by 7.5 kg/cm2 , which is 1.08 times the original balancing force, the recovery force is extremely small and the recovery to the balancing position is very very slowly. For this reason, a general P1 of about 60% of the pressure drop P is preferable, while an axial clearance b of 0.1% to 0.15% of the balance disc diameter is preferable.
Comprehensive discussion of the above can be seen, multi-stage boiler feed pump using balance plate to balance the axial thrust, although the design is very good, but also inevitably induced faltering vibration, which is now the use of high capacity units of high-speed multi-stage boiler feed pump are replaced with balance plate + balance drum or the use of balance drum form to increase the balance of force is the reason.