Background of the invention

This invention relates to a centrifugal pump, intended in particular for gas containing fluids, and method of operating such a pump.

Ribs or bars of the kind comprised in the pump according to the invention are known p e r s e. Up to now they have been inserted into seal housings or casings of pumps for fluids containing particles of an abrasive kind, e.g. sand, i.e. not in pumps for fluids containing more or less gas, such as paper pulp. The purpose of the ribs has been to break a rotating ring of particles, which comes into existence in the seal housing and may cause harmful wear thereof and/or of the seals (the plane seal).

Pump wheels which are provided with one or several apertures also belong to the state of art. Up to now these apertures in the pump wheel have had the purpose of reducing the pressure on the rear side of the wheel inside a rear seal ring or, when the wheel is provided with rear blading, also to pump in cooperation therewith. In pumps for more or less gas (air) containing fluids, mostly paper pulp pumps in practice, air accumulation, which is harmful to the operation of the seal, mostly occurs on the rear side of the pump wheel. A known measure for reducing this accumulation of air consists in connecting the space, where air accumulates, with the suction side of the pump by means of a tube conduit. A drawback of this known measure resides therein, that such an outer connection is cumbersome and has to be made with unreasonably large inside diameter, so that it does not become clogged by

fibres and other solids in the liquid fluid.

Summary of the invention

The principal object of the invention is to eliminate the above drawback and to provide a pump having considerably improved deaeration. This object is attained through the combination defined in claim 1.

The improved deaeration depends, at least mostly, on the fact that the ribs break larger air-bubbles to smaller ones, which more easily are moved out of the seal housing and pass through the apertures in the pump wheel.

A condition for this to occur is the maintenance of an over¬ pressure in the seal housing according to claim 6, so that the flow through the apertures takes place in the right direction. This over-pressure can be attained by making the rear vanes or blades sufficiently small or omitting them.

Brief description of the drawings

Further features and advantages of the pump and the method according to the invention will become apparent from the following detailed description and the annexed drawings, which diagrammatically and as non-limiting example illustrate a presently preferred embodiment of the invention.

Fig. 1 is an axial section basically on line I - I in Fig. 1 through a pump wheel and a seal housing of a centrifugal pump.

Fig. 2 is a cross-section substantially on line II - II in Fig. 1.

Description of the preferred embodiment

In the drawings 1 designates a seal housing which constitutes part of a pump housing cover, 2 a stationary plane seal, 3 a rotating plane seal, and 4 a pump wheel which is fixed onto a pump wheel shaft 8 and is provided with rear vanes or blades 5, which are low not to create an under-pressure.

According to the invention the pump wheel 4 has at least one aperture 6, and the seal housing 1 has at least one rib or bar 7. In the exemplificatory embodiment there is only one aperture, but such apertures may be more numerous, e.g. three or four. The ribs 7, which are integral portions of the seal housing 1 in the exemplificatory embodiment and are two in number, may also be one only or more than two, e.g. four or six. The diameter of the apertures 6 varies in dependence of the pump size and the number of apertures, but is suitably comprised between 3 and 15 mm.

The embodiment described above and illustrated in the drawings is, of course, to be regarded merely as a non- limiting example and may as to its details be modified in several ways within the scope of the annexed claims.