A. The concept of multi-stage pump serial quantity:
In operation, the multi-stage boiler feed water pump is in a state of dynamic equilibrium due to the presence of axial force and the function of the balancing device, that is, the rotor is continuously moving in the axial direction. According to the experimental data, the amount of series motion is between 0.10mm and 0.15mm, and the number of series movements is 10-20/min. This series momentum is not the pumping momentum of the pump discussed in this paper. The serial quantity to be discussed in this paper is balanced. Wear, the amount of movement of the impeller on the suction side under axial force. The amount of water pump has always had different opinions. One view is that when the pump is assembled, the balance device is not installed, the rotor is fixed, and then pushed to the suction end, so that the mouth ring of the impeller is close to the seal ring. The serial quantity is called b1. Then it is pulled to the discharge end, so that the rear cover of the impeller is close to the guide vane. This serial quantity is called b2. The sum of b1 and b2 is called the pump quantity, which is full string. There is also a kind of string, which is b1+b2/2, which is the work string we are talking about. In fact, in reality, these two kinds of views are not strict enough. Because in the operation of the pump, in addition to the stringing of the discharge end at the moment of the start of the pump, the rotor always moves to the suction end under the action of the axial force during operation. What really works is the b1 mentioned earlier, and b2 has no practical meaning. Due to the error of the pump in the assembly process, etc., in general, b1≠b2. The serial quantity should be the distance from the suction side of the impeller to the guide vane when the center line of the impeller and the vane is aligned, which is the b1 mentioned above. It is the maximum amount that the pump can be strung to the suction end during operation. When the center of the vane and the center of the impeller are completely centered in the multi-stage pump operation, the water loss of the pump is the smallest and the efficiency is the highest, which is the ideal economic operation state of the pump. Pumps that are new to the factory and overhauled should be in this state. However, during the operation of the pump, due to the wear of the balance disc, the rotor is gradually moved to the suction side under the action of the axial force until the impeller hits the guide vane.
B. Adjustment of pump serial quantity:
1. The amount of economic operation We all know the performance curve of the pump. If the center of the vane and the center of the impeller are not aligned during the operation of the pump, the optimum operating point will be left, and the efficiency will drop significantly. Generally speaking, the flow is reduced, the lift is increased, and the power consumption is relatively increased. If left unchecked, it can take a full amount of b1 for a long time. This reduces the maintenance time, but the efficiency will be lower and lower. The power consumption will also increase. To this end, it is necessary to select a string with a small amount of maintenance and a small amount of power consumption, so that the pump has a higher efficiency. According to the actual experience, the b1 value we choose should be greater than b1+b2/2. How much should it be? According to the actual situation, we generally choose 0.15mm-0.35mm. If we adjust the pump after overhaul of our company No. 2 When strung, the b1 value is 3.13mm, and the b1+b2/2 is 3.28mm. This string value is determined after taking into account the pump efficiency and adjusting the balance plate and other maintenance.
2. The number of strings after overhaul The pump will inevitably replace or repair some or all of the impellers during overhaul. Due to manufacturing errors, the original amount of movement cannot be guaranteed. Need to readjust. The method is to first measure the amount of the impeller in the inflow section and the middle section of the first stage, and use this as a standard to measure the maximum amount of each impeller one by one, and the value is slightly larger than the inflow section, which can be regarded as qualified. If it is smaller than the inlet section, it must be trimmed. In general, it is adjusted by adding a pad between the middle sections or turning the middle section. Of course, it is necessary to ensure that the relative positions of the rotor components at the axes are unchanged before making adjustments. After the final assembly, due to manufacturing quality and installation process, the serial amount has to be slightly changed, and must be based on the value measured at this time.
C. Adjustment of balance plate gap of multi-stage boiler feed water pump:
For multi-stage boiler feed pumps, there is a lot of information that after the impeller is centered, there should be a gap of about 0.10 mm between the balance disc and the balance sleeve to prevent grinding between the balance disc and the balance sleeve. This is actually not necessary. One is that the high-pressure liquid in the high-pressure chamber where the balance disc is located always moves the balance disc away from the balance sleeve. Even if the pressure in the pump is not established when the pump is started, the axial force caused by the recoil force of the liquid will also be generated. This effect. The second is that the balance device is allowed to wear. The wear of the balance plate ensures that the impeller is not worn. In fact, due to the action of the high-pressure liquid, the minimum clearance between the balance plate and the balance sleeve during the normal operation of the pump is also guaranteed to be around 0.10 mm. There are not many opportunities for grinding. The serious grinding of the balance disc and the balance sleeve is often caused by the poor installation and manufacturing, which causes the balance disc to be skewed. The facts have proved this. Therefore, it is stipulated in the original standard that the verticality of the sealing surface and the axis of the balance plate is required to be <0.03 mm, which is what we call the balance disk sway.
