Causes of hydraulic loss in pipeline flow:
1.Block effect of tube wall roughness
2.The relative motion between the layers of the flow,
3.The vortex of the local sharp change of the water flow in the pipe fitting.
Pipeline (net) hydraulic loss is composed of two parts along the path and the part. In the project, we must calculate the number of the number of its know, in order to correctly select the pump, to determine the required pump head.
Line loss along the way is friction occurs in all processes of water on it, and the wall roughness, length, diameter, velocity and so on, based on the principle of hydraulics, it can establish a relationship. Along with the loss of pipe wall roughness on the frictional coefficient is proportional to the roughness of different pipes, cast iron pipes along the rough, the coefficient of friction is bigger; the plastic pipe is smooth, the coefficient of friction is smaller. And the length of the tube is proportional to the diameter and inversely proportional relationship, that is to say, when the flow rate is small, the diameter is small, the flow rate is fast, then along the path loss is big; but also with the flow rate of square value is proportional to the relationship. Of course, the calculation is more complicated, the simple method can be estimated..
Partial loss of pipeline is the water flowing in the pipe valve, valve, elbow, reducer and other accessories in the process, due to the local device makes the change of flow pattern; flow direction and size change, and the vortex in the flow, the flow of water, the impact of the collision. The hydraulic loss caused by this kind of local resistance is called local loss. The magnitude of the local loss is proportional to the square of the velocity of the flow through the pipe fittings, and is also related to the shape and quantity of the fittings. Parts of the shape change, a large number, the larger the local loss. When the pipeline layout scheme is determined, after the general calculation method to calculate the pipeline loss head, and then determine the pump station design head, to pump type selection. But the calculation program is more complex, for the sake of simplicity, the calculation data can be compiled into a table, in order to check the table to obtain. In addition, can also be a rough estimate: lift loss equivalent to pumping the actual terrain height (the measurement that 30%~50%), small diameter, short pipeline large value; large diameter, long pipeline for small value.
