Author
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Replogle, John |
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Submitted to: Journal of Irrigation and Drainage Engineering
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 3/23/1998 Publication Date: N/A Citation: N/A Interpretive Summary: Discharges from irrigation wells frequently spill directly into canals. Often we want to measure these flows in efforts to improve irrigation water management, but many conditions make this task difficult. Sometimes the pipe does not flow full. Sometimes the pipe outlet end is corroded and jagged, limiting the use of many end-attachment meters such as portable, end-cap orifices. If the outfall pipe is too short, elbows or other pipe fittings installed upstream in the pipe may produce a distorted flow profile that is detrimental to the proper installation and operation of commonly available pipe flow meters. An economical field method of evaluating the result of a meter installed in this compromised situation is described. The device can be constructed using common shop techniques and standard small pipe fittings. It is portable and disassembles to fit into a standard business brief case. The proper application techniques are described in detail for use by field technicians. The process is relatively straightforward and does not require drilling holes in the well pipe. It provides the capability of measuring the flow from pipes in their existing status of corrosion or partial flow without the necessity of seeking permission to drill holes or permanently altering an installation. It provides irrigation district technicians a convenient and needed tool for evaluating existing meter installations and for measuring discharges from previously unmeasured wells. Technical Abstract: Irrigation wells frequently discharge directly into canals. Upstream elbows, the pump head, or other pipe fittings may produce a distorted flow profile that is detrimental to the proper installation and operation of commonly available pipe meters. Before attempting to condition the flow with longer discharge piping or straightening vanes, it is desirable to know how distorted the flow profile really is. If this information can be provided, the meter technician can determine whether a correction in the meter coefficient will suffice, or if flow conditioning equipment is needed, or whether flow conditioning equipment, if already installed, is working effectively. An economical method for field evaluating the result of an installed meter in this compromised situation is described. The method uses a conveniently fashioned Pitot-tube system that can be clamped to the pump discharge pipe. This system is used to detect quickly the velocity at several points across the pipe diameter. Distorted profiles can be detected and measured. Pitot-tube systems have long been used in pipe flows. Most require that special taps be drilled in the outflow pipe of the well. Some use special double-tube constructions that are difficult to build using simple machine shop procedures. This Pitot impact tube, with its static pressure companion tube, can be constructed using common shop techniques and standard small pipe fittings. |
