Motor pump with a treating liquid circulation system

Abstract: In a motor pump where the cooling of the motor section (22) and the lubrication of bearings (28 and 30) are achieved by an independent circulation system of a treating liquid by an auxiliary impeller (38), the pressure of a motor section (22), that is, the pressure of the treating liquid circulating is raised more than the suction pressure of a main process (the suction pressure of a main impeller (12)). The treating liquid circulating from a front rotor chamber (34) is caused to flow through a passage (60) into an inlet port (62) which is separated radially outside by a distance L from a suction inlet portion (52) of the auxiliary impeller (38). This raises the pressure at the inlet port (62) (the pressure of the front rotor chamber (34)) to a pressure which is higher than the pressure at the suction inlet port (52) by a magnitude corresponding to the distance L. Thus, even for a liquid which is at a high temperature and liable to be gasificated, it is possible to prevent the gasification of the circulating liquid to thereby achieve the cooling of the motor section (22) and the lubrication of the bearings (28 and 30) in a smooth fashion.

Description: The present invention relates to a motor pump, and more particularly to a canned motor pump having a circulation system for a treating liquid circulating within a rotor chamber of a canned motor section for cooling the motor section and for lubricating its bearing. From US-Patent 3,637,329 a motor pump is known which comprises an auxiliary impeller for supplying treating liquid for cooling purposes in order to establish a high temperature operation. However, although an auxiliary impeller is established and special means are provided for cooling, the effect is poor, and it would be desirable to have a better cooling via the rotor/stator assembly. It would be possible to enlarge the auxiliary impeller in order to improve cooling. However, this would reduce the efficiency of the pump such that it is undesirable. From GB-A-936 727 a motor pump is known which comprises an auxiliary impeller for pumping treating liquid for lubricating and cooling the motor section. A throttle is provided for regulating the lubricating and cooling. However, pumping against a throttle is unefficient and also increases the temperature of the treating liquid. In general, a canned motor pump, as shown in Figure 2, essentially comprises a pump section 16 and a canned motor section 22. The pump section 16 includes a casing 10, a main impeller 12 and a liner disc 14. The canned motor section 22 includes a stator assembly 18 and a rotor assembly 20. Both the pump section 16 and the rotor assembly 20 are respectively mounted on a rotor shaft 32 which is supported by a liner ring 26, a front bearing 28 and a rear bearing 30. In such canned motor pumps, the rotor shaft 32 is not sealed. Then, the treating liquid of the canned motor pump serves to cool the motor section 22 and to lubricate the front and rear bearings 28 and 30. With respect to canned motor pumps resistive to a hot treating liquid, The circulation of the treating liquid for cooling the motor section 22 and lubricating the front and rear bearings 28 and 30 are achieved by an auxiliary impeller 38 independent of the main impeller 12. The auxiliary impeller 38 is provided on a side of a front rotor chamber 34 involved in the motor section 22. Thus, the auxiliary impeller 38 serves for making the pressure of the treating liquid raise. Then, the treating liquid is circulated through a pipeline 40, a cooler 42, a pipeline 44, a liquid reservoir 46, a passage 46 and a surface of the rear bearing 30, a rear rotor chamber 36, the front rotor chamber 34, a passage 50 and a surface of the front bearing 28 and thus back to the auxiliary impeller 38. As a result of those, the cooling for the motor section 22 and lubricating for the front and rear bearings 28 and 30 are achieved. Although such circulation of the treating liquid for cooling and lubricating operations are achieved by the auxiliary impeller 38 independent of the main impeller 12, such circulation system is poor in reliability, especially to a high temperature treating liquid which is likely to be gasified. In Figure 3 showing the auxiliary impeller 38 section, the treating liquid in the front rotor chamber 34 is transmitted to a suction inlet port 52 of the auxiliary impeller 38 through the passage 50 and the bearing surface of the front bearing 28. In the auxiliary impeller 38, the pressure of the treating liquid is raised and discharged through a discharging port 54. With respect to the pressure of the treating liquid, since the suction inlet port 52 communicates with a suction inlet port of the main impeller 12 through passage 56 and the liner ring 26 (see Figure 2), a suction pressure of the treating liquid at the suction inlet port 52 is so set as to be approximately equivalent to a suction pressure of the treating liquid at the main impeller 12, and thus in a main pumping action (hereinafter referred to as a main process suction pressure). Further, the pressure of the treating liquid in the rotor chamber, particularly in the front rotor chamber 34 directly communicating with the suction inlet port 52 through the passage 50 is also so set as to be approximately equivalent to the suction pressure of the main process. In case that the treating liquid is a high temperature and liable to be gasified, if the treating liquid cooled by the cooler 42 becomes a higher temperature than a predetermined value, the circulating treating liquid is readily gasified. Therefore, the problems with the conventional cooling and lubricating system are that the gasification of the circulating treating liquid prevents the cooling of the motor section and the lubrication of the bearing. Further, the gasification of the circulating treating liquid causes cavitation, erosion and other affections, when bubbles produced by the gasification burst. Accordingly, it is a primary object of the present invention to provide a motor pump including an improved circulation system for a treating liquid circulating within a motor section which is capable of preventing a gasification of the treating liquid due to a high temperature. The above and other objects, features and advantages of the present invention will be apparent from following descriptions. In order to achieve the above object, a motor pump having an additional treating liquid circulation system including an auxiliary impeller provided on a side of the front rotor chamber of the motor section for cooling the motor section and for lubricating its bearings is characterized in that an inlet port into the auxiliary impeller for the treating liquid circulating within the rotor chamber is provided in the radial direction outside a suction inlet port of the auxiliary impeller so that a pressure of the treating liquid within the rotor chamber is raised more than a pressure of the treating liquid at the suction inlet port of the auxiliary impeller. Further, it is preferable to provide a shroud having a predetermined diameter, which is provided to the auxiliary impeller between on a side of the inlet port and the suction inlet port of the auxiliary impeller for the treating liquid which circulates within the rotor chamber. The inlet port of the auxiliary impeller for circulating the treating liquid is provided in the radial direction outside the suction inlet port of the auxiliary impeller. As a result of those, the pressure of the treating liquid circulating within the rotor chamber is higher than the suction pressure of the auxiliary impeller, and thus the suction pressure of the main process. In case that the shroud is provided to the auxiliary impeller on the side of the inlet port and the suction inlet port, the rise in the pressure of the treating liquid circulating in the rotor chamber may suitably be adjusted . Figure 1 is a cross sectional view showing a structure of an auxiliary impeller section involved in a motor section of the motor pump according to the invention. Figure 2 is a cross sectional view showing a structure of a canned motor pump for treating a high temperature liquid which is poor in a heat resistance. Figure 3 is a cross sectional view showing the structure of the conventional auxiliary impeller involved in a motor pump. Preferred embodiments of a motor pump according to the present invention will hereinafter fully be described in detail with reference to the accompanying drawings. In Figure 1, an auxiliary impeller section 38 is so constructed that a treating liquid transmitted from a front rotor chamber 34 flows into an inlet port 62 through the passage 60, and thus into an outside position separated at a predetermined distance L from a suction inlet port 52 of the auxiliary impeller 38. Further, a small portion of the treating liquid flows directly into the suction inlet port 52 through the bearing surface of the front bearing 28. The treating liquid around the auxiliary impeller 38 has a profile in pressure corresponding to a pressure profile possessed by a normal forced swirling motion of the treating liquid by general open radial blades. Thus, the pressure of the treating liquid at the inlet port 62 is higher than the pressure of the treating liquid at the suction inlet port 52, and thus the suction pressure of the main process (the suction pressure of the main impeller 12) by a pressure difference of the treating liquid generated by the distance L. Accordingly, the pressure of the treating liquid within the front rotor chamber 34 communicating with the inlet port 62 through the passage 60 is also raised at least by the same pressure difference as the above pressure difference value. As a result of those, the treating liquid circulating in the rotor chamber is free from any gasification. It is possible to allow a part of a rise in the pressure of the treating liquid to be adjusted, by selecting the location of the inlet port 62, and thus by setting the predetermined distance L. It is further possible to allow that the adjustment of a part of a rise in the pressure of the treating liquid may also be achieved by adjusting a diameter of the shroud 64 corresponding to the variable distance L. This allows preventing an extreme large gradient of the pressure of the treating liquid within the rotor chambers 34 and 36. Thus, the present invention is able to prevent a high temperature treating liquid which is liable to be gasified from any gasification thereby freeing the treating liquid from the cavitation. Thus, the present invention possesses a desirable cooling function for the motor section and lubricating function for the bearings. Needless to say, the present invention is applicable to not only the above type of the canned motor pump but other types of motor pumps, for example, a slurry separation type canned motor pump in which a clean mother treating liquid is supplied to a circulating treating liquid, a canned motor pump having an independent circulating system and an uncanned motor pump. Whereas modifications of the present invention will no doubt be apparent to a person of ordinary skilled in the art, it is to be understood that the embodiments shown and described by way of illustration are by no means intended to be considered in a limiting sense. Accordingly, it is to be intended by the claims to cover all modifications of the invention which fall within the scope of the invention.

Claims: A motor pump having a pump section (16) with a main impeller (12) and an independent treating liquid circulation system including an auxiliary impeller (38) provided on a side of a front rotor chamber (34) of a motor section (22) for cooling and lubricating said motor section (22) with a first treating liquid passage supplying liquid through a bearing (28) for lubricating said bearing (28) and through a suction inlet port (52) of said auxiliary impeller (38), and with a second treating liquid passage (50 ; 60) supplying treating liquid through said front rotor chamber (34) and through a second inlet part (62) of said auxiliary impeller (38), characterized in that said treating liquid is supplied to said auxiliary impeller (38) by said second treating liquid passage (60) radially outward of said suction inlet port (52) so that a pressure of said treating liquid within said rotor chamber (34) is higher than a pressure of said treating liquid at said suction inlet port (52) of said auxiliary impeller (38). The motor pump as claimed in claim 1, characterized in that a shroud (64) having a predetermined diameter is provided on a side of said second inlet port (62) and suction inlet port (52) to said auxiliary impeller (38).

Inventors: NAKAGAWA YUZO, NAKAGAWA, YUZO, Nakagawa, Yuzo c/o Nikkiso Co.,Ltd.
Applicants: NIKKISO CO LTD, NIKKISO CO., LTD.
Application year: 1992
Main classification: F04D29
IPC codes: F04D29, F04D13