I have no idea what you are calling a "monoblock". Please give a better definition.
As for the submersible pump:
1. A submersible pump will use the fluid being pumped as a cooling medium, to take heat away that the motor is producing.
2. When you run dry, the pump will cavitate. Basically, since it can no longer pump, all of the heat due to friction will be imparted to the fluid remaining in the volute.
3. The above 2 reasons (along with a waste of energy), is why you should have a "low level cutoff" (usually a float switch) in the pump circuit.
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TANSTAAFL (If you don't know what that means, Google it - yourself)
Machines generally don't care if they are loaded or not, but pumps do. A submersible pump should NEVER be run dry. If you need to run the filler/capper in order to set it up or test the timing etc., disable the filling pump first.
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** All I every really wanted to be, was... A LUMBERJACK!.**
When a centrifugal pump runs without water, shaft,seal/gland packing etc will be overheated but motor may not burn out.Give details (type/model/brand etc)of your mono-block pump/deep-well submersible pump/drainage pumps. In deep well submersible pumps bearings and motor are water cooled,if no water they will get overheated. In sewage/drainage submersible pumps motor may be oil cooled so when you run without water what did you observe?.
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