booster pump

Hi, I have recently replaced an old booster pump, which was well nackered, with a new Clarke CBM250SS. I had hoped to reuse the current plumbing as entry/exit were in the same places BUT the installation guide says that the delivery (i.e. output) hose must rise 70cm before any elbows are attached. This means re-arranging all the plumbing on the output side as the 1st elbow is about 15cm above the outlet. Can anyone explain why this 70cm is necessary? It is only for the CBM250SS and none of the other similar pumps covered by the same manual.
Thanks in advance
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Ask machine mart? Watch out for their returns strategy should you wish to return it.... UK.d-i-y passim....
Jim K
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Brother bought a Clarke sump pump, and it was very difficult to get it to prime properly. Basically, had to detach the output hose, start it and wait until the output was at full pelt, and then reattach hose with it still running. Even submerged, it could not force the air out of the pump with any hose on the outlet, even though the hose was not presenting any significant resistance.
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Andrew Gabriel
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