Multi stage pump thrust balance device inspection and maintenance requirements
The balance device of the multi-stage pump consists of a balance plate mounted on the shaft and a balance ring fixed on the pump body, as shown in below picture.
The balance plate 1 rotates with the pump shaft, and the balance ring 2 is inlaid on the pump body. An axial gap of 0.01 to 0.25 mm is reserved between the balance plate and the balance ring. The cavity behind the balance disc is connected with the last stage impeller inlet of the pump, and the pressure is low; the pressure of the liquid in the gap between the balance disc and the balance ring is close to the pressure at the outlet of the last stage impeller, and the pressure is higher, so that a balance is formed The pressure difference on both sides of the disc. This pressure difference acts on the pump shaft through the balance plate, and the resulting tension is called the balance force, and the direction is opposite to the axial force acting on the impeller.
When the multi-stage pump works, when the axial force on the impeller is greater than the balance force on the balance plate, the pump rotor will move in the suction direction, which reduces the axial clearance of the balance plate and increases the fluid resistance of the liquid. This reduces the amount of leakage. After the leakage is reduced, the pressure drop of the liquid flowing through the radial gap is reduced, thereby increasing the pressure in front of the balance plate, that is, increasing the balance force on the balance plate. As the balance plate moves to the left, the balance force gradually increases. When the balance plate moves to a certain position, the balance force is equal to the axial force and balance is reached.
Similarly, when the axial force is less than the balance force, the rotor will move to the right. After a certain distance, the axial force and the balance force will reach a new balance. Due to inertia, the moving rotor will not immediately stop at the new balance position, but continue to move to promote the destruction of the balance, resulting in conditions for the rotor to move in the opposite direction.
The key part of the thrust balance device is the working surface of the balance plate and the balance ring. If there is a skew or unevenness between the two working surfaces, a large amount of leakage will occur when the pump is running, and the balance chamber cannot maintain a balanced axial thrust. Due to the pressure, the effect of balancing the axial force is lost.
The balance plate is installed on the pump shaft, which may form an eccentricity with the pump shaft, causing the rotor to vibrate during operation. This vibration will affect the normal operation of the bearing and the pump shaft. In severe cases, the pump shaft and the bearing may be damaged. This amount of eccentricity should be strictly controlled.
The verticality between the balance plate and the pump shaft is obtained by measuring the end circle runout of the working surface of the balance plate. The eccentricity between the balance disk and the pump shaft is obtained by measuring the radial runout of the balance disk hub.
To measure the circular runout of the end face of the balance plate, the balance plate should be installed on the pump shaft, and the pump shaft should be supported by the two tops of the lathe to prevent the axial movement of the pump shaft, and then set the balance plate on the working surface side of the balance plate. The dial indicator makes the contact of the dial indicator vertically contact the working surface of the balance plate.
To measure the radial runout of the balance disc hub, a dial indicator should be installed next to the hub so that the contacts of the dial indicator vertically contact the outer circular surface of the hub, as shown in Figure 2. Then, slowly rotate the balance plate one week, and the difference between the maximum reading and the minimum reading of the dial indicator in contact with the working surface of the balance plate is the end face of the balance plate, and the maximum reading and the minimum reading of the dial indicator in contact with the hub The difference is the radial runout of the hub.
When measuring the runout of the impeller group, install the balance disc on the pump shaft, and measure the end face circular runout of the balance disc and the radial circular runout of the hub at the same time. In this way, it is possible to save the work of re-installing the support when measuring separately.
See below for the allowable value of the end face circular runout of the balance disc and the allowable value of the radial circular runout of the hub.
Allowable value of balance disc circle runout /mm
Diameter of balance disk hub ≤50 51～120 121～260 261～500
The circular runout of the end face of the balance disc 0,04 0.04 0.05 0.0 6
Wheel hub radial runout 0.03 0.04 0.05 0.06
If the amount of runout exceeds the value specified above, the balance plate can be stuck on the lathe together with the pump shaft, and the amount of runout can be reduced by turning. After turning, in order to reduce the vibration during operation, the balance plate should be statically balanced. In order to reduce the leakage of liquid in the balance chamber, the surface roughness of the working surface of the balance plate and the balance ring are required to be no greater than Ra 1.6μm.
