Case Studies of Semi-Closed Pipeline Systems for Flexible Deliveries

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by John L. Merriam, Calif. Polytechnic St. Univ, San Luis Obispo, United States,

Document Type: Proceeding Paper

Part of: Irrigation and Drainage: Saving a Threatened Resource—In Search of Solutions

Abstract: The semi-closed pipeline system using the best aspects of the open and the closed pipeline systems, has many applications. It is the best adapted system for use with the variable flow rates occurring with the use of flexible schedules. The open system is capable of limiting the maximum head in the system facilitating the use of low pressure irrigation pipe and a stable outlet head. It cannot operate to modify flow rates by downstream control and so cannot be automated. It is susceptible to air entrainment and surging. The closed system with various classes of pipe can operate at any desirable maximum pressure. It permits downstream control of the outlet flow rate so is capable of downstream automated control. However, with variations in flow rate, the pressure variations cause an undesirable condition at outlets so special flow or pressure stabilizing facilities are needed. The semi-closed system utilizing float valves, operates at a stable low head, avoids air entrainment and surges, and can operate with downstream control permitting automation of a system. Case studies of the use of semi-closed systems and the advantage in operation of a low, stable pressure with varying flow rates automatically controlled at the turnout valve, are presented for an irrigation district, a pilot project in a developing country (India), and for farming operations.

Subject Headings: Case studies | Pressure pipes | Flow rates | Flow control | Pipelines | Pressurized flow | Automation | Flexible pipes | Irrigation systems | Rivers and streams | India | Asia

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