Reasons for hydraulic loss caused by pipeline flow are: first, the rough blockage effect of the pipe wall; second, the relative movement between layers of the water flow; and third, the vortex formed by the local rapid change of the flow in the pipe fittings. Pipeline (network) hydraulic loss consists of two parts: along the way and partly. In engineering, we must calculate how much it knows, in order to correctly select the pump and determine the required pump head.
The loss along the pipeline is the frictional resistance that occurs in the entire flow of the water flow. It is related to the roughness of the pipe wall, pipe length, pipe diameter, and flow velocity. According to the principle of hydraulics, it can establish its relationship. The coefficient of friction along the path along the pipe wall roughness is proportional to the friction coefficient. Different pipes have different roughness. The cast iron pipe is rough and the coefficient of friction along the path is larger; the plastic pipe is relatively smooth, and the coefficient of friction along the path is small. some. It is proportional to the length of the pipe; inversely proportional to the pipe diameter, that is, when the flow is constant, the pipe diameter is small, and the flow rate is fast, the loss is large along the course; it is also proportional to the square of the flow velocity. Of course, calculations are cumbersome and simple methods can be estimated.
Pipeline local loss is the flow of water through the bottom valve, valve, elbow, different diameter pipe and other accessories in the pipeline, due to the local device to change the flow pattern; flow direction and size change, and the flow of vortices, so that the flow Collide with each other and impact. The hydraulic loss caused by this local resistance is called local loss. The size of the local loss is proportional to the square of the velocity of the water flowing through the pipe fittings, and it is also related to the shape and quantity of the fittings. Large variations in the shape of the cross-section of the fittings, with a greater number, result in greater local losses. After the pipeline layout plan is determined, generally, the pipeline loss head is obtained through the calculation method, and then the design head of the pumping station is determined so that the pump selection can be performed. However, the calculation procedure is more complicated. For the sake of simplicity, the calculation data can be compiled into a table so that the table can be obtained. In addition, a rough estimate can also be made: the loss head is equivalent to 3 to 50% of the actual topographic lift height (measured), the pipe diameter is small, and the pipeline is shorted to a large value; the pipe diameter is large and the pipe length is taken as a small value.
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