Pump impeller

Abstract: The invention concerns a centrifugal pump impeller for pumping of liquids containing solid pollutions. According to the invention the impeller (5) is on its back side provided with back vanes (8) for circulation of cooling liquid for the electric motor of the pump, a narrow slot (11) being provided between the impeller (5) and the pump housing (10) through which cooling liquid is taken in, said slot at certain areas being widened by help of axially directed grooves (12) at the tips of the back vanes (8).

Description: The invention concerns a centrifugal pump meant for pumping of liquids containing solid pollution. A common pump type is the so-called submersible pump where the pump and an electric motor as a unit is submersed in the pumped medium, the motor normally obtaining its cooling directly from the surrounding, pumped medium. If however, the level of the liquid decreases such that the motor is surrounded by air, the cooling may be insufficient and therefore the motor is often provided with an internal cooling system where the pumped medium is used. An example of such a solution is shown in the Swedish Patent No 367 465. As the pumped medium often contains pollutions, said patent suggests a narrow slot to be arranged between the impeller and the pump housing through which comparatively clean water is fed into the cooling water room between the pump and the motor, where the water is circulated by help of vanes at the back of the impeller. The slot prevents pollutions from going into the cooling water room thus diminishing the risks for clogging of the cooling channels around the motor. According to a further development of subject patent, vanes are arranged within the cooling jacket which transport the cooling liquid a distance upwards thus obtaining a cooling of the entire motor. At pump start air bubbles may collect within the cooling water room at the back of the impeller. This may cause that the vanes will not be able to grip the liquid and thus no circulation is obtained. According to the invention the problem with the air bubbles is solved by a specific design of the impeller as stated in the claim. The invention is described more closely below with reference to the enclosed drawings. Fig 1 shows the principle for a cooling system according to the invention, while Fig 2 and 3 show the impeller from two views. In the drawings 1 stands for a pump housing, 2 an electric motor surrounded by a cooling jacket 3 having vanes 4 for circulation. 5 stands for a pump impeller having inlet 6, main vanes 7 and back vanes 8. 9 stands for a ring formed part, 10 a part of the pump housing, 11 a slot, 12 axially directed grooves and 13 an exhaust pipe. Fig 1 shows the principle for cooling of the motor 2 by help of pumped liquid. The latter is fed through a narrow slot 11 between the impeller 5 and the pump housing 1. The liquid is circulated around the motor within a slot under the jacket 3. The exhaust pipe 13 direct air bubbles from the upper part of the jacket where the air is compressed. As is shown in Fig 2 there is an axially directed slot 11 between a ring formed extension 9 on the impeller 5 and a corresponding extension 10 at the pump housing 1. Liquid is fed through this slot into the space behind, above the impeller. The back vanes 8 operate in said space to obtain the circulation (C) of cooling medium around the motor. As is shown in Fig 3, the vanes start a distance outwards from the center of the impeller and end at the ring formed extension 9 previously mentioned. The air present in the cooling water space at pump start which makes the pumping of the cooling medium more difficult, is collected at the back sides of the vanes 8 and particularly at their tips. An effective deaeration is, according to the invention, obtained by help of the ring formed extension 9 being provided with axially directed grooves 12 in front of the back sides of the vanes 5. By help of these limited broadenings of the slot the air bubbles are directed outwards to the pumped medium (D) and thus constitute no hinderance to the pumping of the cooling medium. Tests have proven that the evacuation time has been reduced to one third of the normal time. As the grooves 12 are arranged at the tips of the vanes, there is no risk that pollution from the pumped medium should enter the broadened slot.

Claims: A centrifugal pump for pumping liquids containing solid bodies, comprising an impeller with a central, axially directed inlet (6) and a number of radially or tangentially directed vanes (7) which between themselves create the outlet of the impeller (5), said impeller at its rear side being provided with a number of rear vanes (8) for pumping of cooling liquid to be circulated around the electric motor (2) driving the pump, said cooling liquid being fed through a circular axially directed slot (11) at or near the circumference of the impeller, characterized in that the slot (11) is created by a ring shaped extension (9) on the rear side of the impeller (5) and a non-rotary part (10) of the pump housing (1) situated radially inward of said extension (9), that the tips of the rear vanes (8) are situated close to the extension (9) and that the latter is provided with axially directed grooves (12) at the vane tips which widen the slot (11) in these areas.

Inventors: BRANDT BENGT AKE, BRANDT, BENGT AKE
Applicants: FLYGT AB ITT, ITT FLYGT AKTIEBOLAG
Application year: 1992
Main classification: F04D7
IPC codes: F04D29