"This alternative is to install the pump on the other side of the bank of the lagoon and extend the suction pipes to the lagoon over the bank. The total length of the suction pipe would be about 40 m"
http://www.google.ps/url?sa=t&source=web&cd=1&ved=0CBUQFjAA&...

"For higher Manometric suction lifts, up to a maximum of 6-7m pump capacities are reduced. The suction pipe must be perfectly airtight and to ensure the performance curves shown in the catalogue, sizes should be as following"
http://www.google.ps/url?sa=t&source=web&cd=3&ved=0CB8QFjAC&...



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Note added at 2 hrs (2011-02-18 12:50:02 GMT)
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مصطلحات الاستزراع المائي، منظمة الأغذية والزراعة - الفاو

Valve, non return-
Pipe fitting, which permits the flow of water through it in only one direction. Used for applications such as the end of suction pipes, where, when the suction pump is turned off, the pipe must remain full of water.

صمام عدم الرجوع
صمام يثبت على الأنبوب ويسمح بمرور الماء فيه في اتجاه واحد
فقط. ويستخدم في تطبيقات مثل نهاية مواسير السحب، بحيث إذا
أُغلقت مضخة السحب يظل الأنبوب ممتلئا بالماء.