According to the principle of fluid mechanics, when the pump is running, pressure water moves at a certain speed in the pipeline system. When the speed direction and size change, the pipeline system will generate a dynamic reaction. The main pipeline that generates the reaction force is the outlet of the outlet pipe, and the outlet pipe of the check valve is the outlet of the outlet pipe.
According to the principle of theoretical mechanics and material mechanics, the pump is transmitted by the pipeline system to the fulcrum through the pipeline, but the fulcrum will not receive the same force. The pipeline connected to the pump is equivalent to a beam member and a discharge valve.
That is, each section will be subjected to bending moments, especially when the bearing capacity of the fulcrum is small or even suspended, the entire pipeline becomes a cantilever beam from the fulcrum to the right, and the pump inlet and outlet will bear a huge bending moment. The position where the pump breaks is at the pump outlet section, and the crack shape of the fracture surface is inclined, which is at an angle to the horizontal line.
According to the fracture location and the fracture crack shape, and according to the force analysis, it can be basically concluded that due to the installation, the support pre-tightening force between the fulcrums is insufficient or there is no supporting force (floating), and there is no fulcrum at the pump outlet bend. , causing the pipe to become a quasi-cantilever beam (complete cantilever beam when suspended). The pump is close to the fulcrum, and the bending moment of the pipeline section near the pump is relatively large. Because the bending section modulus of the pump outlet section is the smallest, when the pump is stopped, only the static force exists in the pipeline system.
The section can withstand the bending moment generated by static force, but when the pump is running for a period of time, on the one hand, it will generate dynamic reaction force, on the other hand, it will continuously vibrate and other external forces (including the water hammer pressure when the pump is stopped), causing the section to be bent. The moment increases and the fracture occurs.
