By Neumaier R.

The improvement of airtight (sealless) pumps during the last part century are traced and up to date layout options are defined. the present kingdom of the expertise is analyzed. The layout, functionality, and alertness of airtight centrifugal pumps and rotary displacement pumps are studied.

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Canned motor pumps and magnetic drive pumps) When operating such pumps in the overload range, which can occur when pumping without throttling control, the maximum flow rate specified by the manufacturer may be exceeded, and for self-priming centrifugal pumps this can lead to thermal overload of the motor. In the case of canned motor pumps and magnetic drive pumps where no additional pressure increase of the partial flow is provided for by means of an auxiliary impeller, then an impermissible temperature rise can occur due to the smaller pressure gradient and this results in a reduction in the stator-clearance flow.

The disadvantage of this is that the required status has to be established by throttling using a gate valve or orifice. Another possibility is to return part of the flow through a bypass into the suction or supply vessel. Both these methods of adjusting the operating parameters are, however, associated with energy losses which under certain circumstances can be of an unacceptable magnitude. NB! (canned motor pumps and magnetic drive pumps) When operating such pumps in the overload range, which can occur when pumping without throttling control, the maximum flow rate specified by the manufacturer may be exceeded, and for self-priming centrifugal pumps this can lead to thermal overload of the motor.

That duty point B and the point of best efficiency coincide. As can also be seen from Fig. 10, the power input for self priming centrifugal pumps is lower up to average specific rotational speed with increasing rate of flow and reducing head. When designing the drive motor, care should be taken to ensure that no motor overload occurs with a fluctuating head and there is still adequate reserve. 1 Change in the rate of flow Q for a change in static head Hst with the hydrodynamic component remaining constant at the system head curve As can be seen from Fig.

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