Should an expansion joint be installed at the water pump outlet?
Thread Content
Thank you very much for expressing your views on the following two issues.: 1: Should expansion joints be installed at the outlet of medium and large water pumps? What are the pros and cons of expansion joints and rigid connections? 2: After installing the expansion joint, there is basically no vibration after starting the water pump. Why does the vibration become larger and larger when the valve is gradually opened? How to prevent vibration in similar installation methods?
A flexible interface should be installed, mainly to prevent vibration damage to the equipment. There are many reasons for the vibration of the unit and pump room building. Some factors are both related and interactive. In summary, there are mainly four reasons. 1. Electrically, the motor is the main equipment of the unit. The internal magnetic imbalance of the motor and the imbalance of other electrical systems often cause vibration and noise. For example, when an asynchronous motor is running, the radial alternating magnetic pull between the stator and the rotor generated by the interaction of stator and rotor tooth harmonic flux, or when a large synchronous motor is running, the magnetic center of the stator and rotor is inconsistent or the air gap difference in each direction exceeds the allowable deviation value, etc., may cause periodic vibration and noise of the motor. 2. Mechanically, the quality of the rotating parts of the motor and water pump is unbalanced, shoddily manufactured, poor installation quality, the axis of the unit is asymmetrical, the swing exceeds the allowable value, the mechanical strength and stiffness of the parts are poor, the bearings and sealing parts are worn and damaged, and the critical speed of the water pump resonates with the natural frequency of the unit, etc., which will produce strong vibration and noise. 3. In terms of hydraulics, uneven flow rate and pressure distribution at the pump inlet, pressure pulsation of the working liquid at the pump inlet and outlet, liquid flow around, deviation and deflow, non-rated operating conditions and pump cavitation caused by various reasons, etc., are all common causes of vibration of the pump unit. Rapid changes in pressure in water pipelines and water hammer caused by dynamic transition processes such as starting and stopping of water pumps, opening and closing of valves, changes in working conditions, and emergency shutdowns due to accidents often cause vibrations in pump rooms and units. 4. Unreasonable design of the water inlet channel of the unit in hydraulic and other aspects or unmatched with the unit, improper submersion depth of the water pump, and unreasonable start and stop sequence of the unit will worsen the water inlet conditions, generate vortices, induce cavitation, or aggravate the vibration of the unit and pump room. When starting a unit that uses a siphon-destroying vacuum cutoff, if air entrainment is difficult in the hump section, the siphoning time will be too long. ； The design of the flap door of the unit with a flap door cutoff is unreasonable, and it opens and closes constantly, constantly hitting the flap door seat. ； Uneven subsidence of the foundation supporting the water pump and motor or poor rigidity of the foundation will also cause the unit to vibrate.
The main function of the expansion joint is to absorb thermal expansion, not to absorb shock. If an expansion joint is installed on a pipe with strong vibration, it will cause hidden dangers. The expansion joint can easily become loose and damaged. There are many reasons why the machine pump vibrates. The explanation above is more clear. It is necessary to analyze the specific reasons and prescribe the right medicine.
If the inlet and outlet of the pump meet the stress calculation and the stress is eliminated, then there is no need for Peng Zhang.
Expansion joints are installed to eliminate the stress caused by excessive temperature differences. They are pipeline accessories and have little impact on the equipment.
The expansion joint you mentioned should be a rubber soft joint. All rubber joints are used at low temperatures. This must be installed, especially when there is no natural compensation in the inlet and outlet pipes. If not installed, after the water pump is repaired, after the water pump and motor coupling are aligned, when the bolts of the water pump inlet and outlet flanges are tightened, the locking force can easily cause the water pump to shift, causing the coupling to deviate, fail to align, and cause vibration at startup. The above is for reference. I don’t know what everyone’s opinion is.
It is rare to press an expansion joint at the pump outlet. The function of the expansion joint is to prevent the thermal expansion and contraction of the pipeline from damaging the pipeline. It is not said that the expansion joint is pressed to prevent vibration.
1# iwaszl What the second floor said makes sense, learn from it* . If the vibration is caused when the valve is opened, the water passing through the valve is caused by disturbance. Can the valve be replaced?
The use of expansion joints should be avoided unless necessary, especially when transporting corrosive fluids. Expansion joints are generally weak links damaged by corrosion.
I don't think it should be installed, the expansion joint is not for the shock absorbing aspect of the application. The vibration of the pipeline is caused by the impact of the water flow during the process of opening the pump valve.
The poster may be wrong. Generally, the medium temperature of water pumps is not high, so expansion joints are not needed. Generally, flexible joints should be added to the water pump outlet to reduce vibration and noise.