The pumped medium must be completely drained from the pump chambers.
During frost periods, users often fail to ensure that the pumped medium is drained completely from the pump chambers.
If the pump is operating too far to left on the curve, this simply means that the pump is delivering high pressure but at a flow rate that is low or non-existent. High pressure inside the pump stresses the impeller unit and thus increases pressure on the motor bearings.
When a pump operates too far to the right on the curve, this simply means that the pump is delivering a flow rate greater than that for which it was designed. In other words:
Unless specified to the contrary, the curves in the Grundfos documentation are specified for the density and viscosity of water at a temperature of 20°C (specific gravity = 1 and viscosity = 1).
A cooling jacket, also referred to as a flow generator, ensures that there is always sufficient water flow across the motor surface in order to cool the motor.
In a dry-running pump, the component that comes into contact with the medium (the wetted part) is separate from the motor.
In this pump design, all rotating parts (shaft, rotor, impeller) are located within the can in the pumped medium. Cooling and lubrication is provided by the pumped medium.
The pump's input power is the pump's power requirement under the present operating conditions.