Differentiating the Pump Models of Garden Pumps
The pump head does not refer to the geodetic head (geodetic means a normal height difference, for example on a hill), but to the possible height of the water column in meters that the pump can pump, in this case a suction pipe to this length, which must be overcome. The water column in meters indicates the negative pressure that can suck a pump. Between our atmospheric pressure and a pressure of 0 one speaks of negative pressure, under zero on the other hand begins the vacuum, which pumps, if at all, can pull only in a completely closed system.
When venting a centrifugal pump, it is really necessary to vent completely. Even high-quality pumps can no longer deliver air with a share of more than 8 percent. However, if the suction line is leaking, air is sucked in and cavitation occurs. Under "Garden pump does not suck" you will learn what can be responsible if you can not vent the pump as it should.