Bilge pumps and airlocks

[vyv_cox]

If you look at the design of this pump here I think you will see what I mean. The discharge nozzle is sited quite high up the body of the pump and angled upwards, suggesting to me that the pump needs quite a bit of water inside it to begin pumping. A water lock downstream would almost certainly prevent the required level from being achieved. I assume this is the reason that the manufacturers are so insistent that the hose should be continuously rising. It says: Note: In order to prevent air locks it is important that the hose not be allowed to dip below the pump outlet. The hose should be constantly rising.

Also note that a non-return valve is incorporated in the pump.

 

[earlybird]

OK, can't argue against "the book" although it was probably written in China! I see that it also recommends putting the outlet as high as possible, but I won't be taking that advice too literally. I can get hold of a small pump, and, as an un-reformed cynic, I'll set up a test rig at home, when I can get round to it!!