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What's the Reason for the Large Vibration of the Vertical Turbine Pump?

Categories:Technology Service Author: Origin:Origin Time of issue:2022-09-01
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Analysis of the causes of vibration of the vertical turbine pump


1. Vibration caused by the installation and assembly deviation of thevertical turbine pump
After installation, the difference between the levelness of the pump body and the thrust pad and the verticality of the lift pipe will cause the vibration of the pump body, and these three control values are also related to a certain extent. After the pump body is installed, the length of the lift pipe and the pump head (without the filter screen) is 26m, and they are all suspended. If the vertical deviation of the lifting pipe is too large, the pump will cause severe vibration of the lifting pipe and the shaft when the pump rotates. If the lift pipe is too vertical, alternating stress will be generated during the operation of the pump, resulting in the breakage of the lift pipe. After the deep well pump is assembled, the verticality error of the lift pipe should be controlled within 2mm within the total length. The vertical and horizontal error is 0 pump.05/l000mm. The static balance tolerance of the pump head impeller is not more than 100g, and there should be 8-12mm upper and lower serial clearance after assembly. The installation and assembly clearance error is an important reason for the vibration of the pump body.

2. The whirl of the drive shaft of  pump
Whirl, also known as "spin", is the self-excited vibration of the rotating shaft, which neither has the characteristics of free vibration nor is it a type of forced vibration. It is characterized by the rotational movement of the shaft between the bearings, which does not occur when the shaft reaches the critical speed, but occurs in a large range, which is less related to the speed of the shaft itself. The swing of the deep well pump is mainly caused by insufficient bearing lubrication. If the gap between the shaft and the bearing is large, the direction of rotation is opposite to that of the shaft, which is also called the shaking of the shaft. In particular, the drive shaft of the deep well pump is long, and the fitting clearance between the rubber bearing and the shaft is 0.20-0.30mm. When there is a certain clearance between the shaft and the bearing, the shaft is different from the bearing, the center distance is large, and the clearance lacks lubrication, such as the deep well pump rubber bearing lubrication The water supply pipe is broken. Blocked. Misoperation leads to insufficient or untimely water supply, and it is more likely to shake. The journal is slightly in contact with the rubber bearing. The journal is subjected to the tangential force of the bearing. The direction of the force is opposite to the direction of the shaft speed. In the cutting direction of the contact point of the bearing wall, there is a tendency to move downward, so the journal purely rolls along the bearing wall, which is equivalent to a pair of internal gears, forming a rotational motion opposite to the direction of shaft rotation.

This has been confirmed by the situation in our daily operation, which will also cause the rubber bearing to burn out for a little longer.

3. Vibration caused by the overload of the vertical turbine pump
The thrust pad of the pump body adopts tin-based babbitt alloy, and the allowable load is 18MPa (180kgf/cm2). When the pump body is started, the lubrication of the thrust pad is in the state of boundary lubrication. An electric butterfly valve and a manual gate valve are installed at the water outlet of the pump body. When the pump starts, open the electric butterfly valve. Due to the deposition of silt, the valve plate cannot be opened or the manual gate valve is closed due to human factors, and the exhaust is not timely, which will cause the pump body to vibrate violently and the thrust pad will burn out quickly.

4. Turbulent vibration at the outlet of the vertical turbine pump. 
The pump outlets are set in sequence. Dg500 short pipe. Check valve. Electric butterfly valve. Manual valve. Main pipe and water hammer eliminator. The turbulent movement of water produces irregular pulsation phenomenon. In addition to the blockage of each valve, the local resistance is large, resulting in the increase of momentum and pressure. Changes, acting on the vibration of the pipe wall and the pump body, can observe the pulsation phenomenon of the pressure gauge value. The pulsating pressure and velocity fields in turbulent flow are continuously transferred to the pump body. When the dominant frequency of the turbulent flow is similar to the natural frequency of the deep well pump system, the system should absorb energy and cause vibration. To reduce the effect of this vibration, the valve should be fully open and the spool should be of appropriate length and support. After this treatment, the vibration value was significantly reduced.

5. Torsional vibration of the vertical pump
The connection between the long shaft deep well pump and the motor adopts an elastic coupling, and the total length of the drive shaft is 24.94m. During the operation of the pump, there is a superposition of main vibrations of different angular frequencies. The result of the synthesis of two simple resonances at different angular frequencies is not necessarily simple harmonic vibration, that is, torsional vibration with two degrees of freedom in the pump body, which is unavoidable. This vibration mainly affects and damages the thrust pads. Therefore, in the case of ensuring that each plane thrust pad has a corresponding oil wedge, change the 68# oil specified in the original equipment random instructions to 100# oil to increase the viscosity of the thrust pad lubricating oil and prevent the hydraulic lubricating film of the thrust pad. formation and maintenance.

6. Vibration caused by mutual influence of the pumps installed on the same beam
The deep well pump and motor are installed on two sections of 1450 mmx410mm on reinforced concrete frame beams, the concentrated mass of each pump and motor is 18t, the running vibration of two adjacent pumps on the same frame beam is another two free Vibration system. When the vibration of one of the motors exceeds the standard seriously and the test runs without load, that is, the elastic coupling is not connected, and the amplitude value of the motor of the other pump in normal operation rises to 0.15mm. This situation is not easy to detect, and attention should be paid to it.