Patent Publication Number: US-8531070-B2

Title: Pressure-resistant explosion-proof connector

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is the U.S. National Phase of International Application No. PCT/JP2011/052283, entitled “Pressure-Resistant Explosion-Proof Connector”, filed on Feb. 3, 2011, and claiming priority to Japanese Patent Application No. 2010-215053, filed Sep. 27, 2010, the disclosures of which are hereby incorporated by reference in their entireties. 
     TECHNICAL FIELD OF THE INVENTION 
     The present invention generally relates to a pressure-resistant explosion-proof connector for a canned motor pump, and more particularly to a pressure-resistant explosion-proof connector that connects external equipment to a sealed space of a stator portion that is hermetically sealed by an outer cylinder of a canned motor pump, an end bell, and a can in contact with a handled fluid. 
     BACKGROUND OF INVENTION 
     Pressure sensors or gas sensors for use in a flammable/explosive atmosphere such as factories and chemical plants are required to employ a structure meeting construction requirements for electrical equipment for explosive atmospheres. In the construction requirements for explosive atmospheres, various requirements are set for each of an intrinsic safety explosion-proof structure, a pressure-resistant explosion-proof structure, an increased safety explosion-proof structure, or the like. The above sensors preferably employ the intrinsic safety explosion-proof structure that does not trigger explosion as an explosion-proof structure. In the case of the intrinsic safety explosion-proof structure, however, a value of current flowing through equipment is limited, and even general sensors that operate by dry batteries of a few volts, for example, exceed the current limit for the intrinsic safety explosion-proof structure. Thus, it is difficult to employ the intrinsic safety explosion-proof structure. Japanese Patent Laid-Open Publication No. 2009-54940 discloses a pressure-resistant explosion-proof structure for information terminals that allows transmission and reception of information by use of optical communication such as infrared ray by accommodating equipment in a case having an explosion-proof structure in order to externally transmit and receive information in an explosion-proof atmosphere. 
     Flammable substances include a liquid such as petroleum and gas such as LPG and LNG. Highly-volatile petroleum evaporates even at a normal temperature, and its vapor or gas is mixed with the air to be possibly ignited and exploded by electrostatic sparks or faint electric sparks generated when a switch or the like is turned ON/OFF. Here, explosion means combustion accompanied by rapid changes in propagation speed, pressure and temperature. Also, combustion means a chemical reaction in which a substance combines with oxygen in the air, emitting light and heat, and requires a flammable substance, oxygen, and thermal energy such as a flame, electric spark, friction heat and reaction heat necessary for ignition. 
     The explosion-proof structures further include a pressurized explosion-proof structure that prevents a flammable substance from entering a case from outside by enclosing clean air or a nonflammable gas such as nitrogen within the case and thereby setting a pressure therein to be higher than that of the outside. However, when general sensors are used, an air flow or the like may affect measurement. Thus, it is preferable to employ a structure in which flame does not leak outside a case that accommodates the sensors even when combustion or explosion occurs inside the case, and an ignitable gas around the case, if any, is not ignited (the pressure-resistant explosion-proof structure). 
     There has been known a canned motor pump in which a special pressure switch is provided in a terminal box, as disclosed in HERMETIC-Pumpen GmbH, PRODUCT INFORMATION, “Single-stage canned motor pumps complying with the chemical standards”, [online], Aug. 19, 2010, Internet, &lt;URL: http://www.hermetic-pumpen.com/en/hermetic/products.html&gt;.  FIG. 7  is a sectional view of a terminal portion  100 , and shows a terminal box  116  that is fitted with a terminal flange  117  connected to a sealed space of a stator portion. In the terminal flange  117 , a stator coil connection line  111  extending from the stator portion is connected to a terminal  112 , and a pressure switch  113  is arranged in the vicinity of the terminal  112 . The pressure switch  113  has a mechanism whereby a diaphragm is deformed to connect an electric contact when a pressure reaches a preset value. Terminals  114  and  115  of the electric contact are arranged in the terminal box, and a pressure switch connection line is guided to outside from a pressure switch connection line mounting tool  119  of the terminal box  116 . Similarly, the stator coil connection line  111  connected to the terminal is guided to outside from a coil connection line mounting tool  118 . 
     In a canned motor pump, an inner portion of a stator of a motor that drives a centrifugal pump is covered by a can, and a handled liquid (for example, a flammable liquid) is filled therebetween, so that a rotating portion of the pump is immersed in the handled liquid and thus not required to be sealed. Also, since the stator is hermetically sealed by the can, a motor outer cylinder and an end bell, a sealed space is formed in the stator portion. Even when the can is damaged or the like, the liquid does not leak outside but enters the inner portion of the stator. 
     When the handled liquid enters the inner portion of the stator, insulation failure may occur in a stator coil to thereby damage the stator coil. To solve the problem, a pressure switch is provided in the sealed space of the stator portion, to detect a pressure increase due to the liquid leakage of the handled liquid and thereby determine that the liquid is leaking, as disclosed in HERMETIC-Pumpen GmbH, PRODUCT INFORMATION, “Single-stage canned motor pumps complying with the chemical standards”, [online], Aug. 19, 2010, Internet, &lt;URL: http://www.hermetic-pumpen.com/en/hermetic/products.html&gt;. 
     However, when only a small amount of liquid leaks to cause little pressure increase, the pressure switch, as disclosed in HERMETIC-Pumpen GmbH, PRODUCT INFORMATION, “Single-stage canned motor pumps complying with the chemical standards”, [online], Aug. 19, 2010, Internet, &lt;URL: http://www.hermetic-pumpen.com/en/hermetic/products.html&gt;, cannot accurately detect the liquid leakage. To detect such a small amount of liquid leakage, a highly-accurate electrical pressure sensor or a gas sensor needs to be used. When the pressure switch is replaced with the electrical pressure sensor or the gas sensor, the conventional terminal flange  117  including a mounting base needs to be replaced for each sensor, thereby causing an increase in cost. 
     Thus, it is an advantage of the present invention to provide a pressure-resistant explosion-proof connector that allows even a different type of sensor to be mounted via a common connector and thereby eliminates the need for replacement of a connector including a mounting base for each sensor. 
     SUMMARY OF THE INVENTION 
     To achieve the above advantage, a pressure-resistant explosion-proof connector according to the present invention is a pressure-resistant explosion-proof connector that connects external equipment to a sealed space of a stator portion hermetically sealed by a can in contact with handled fluid, an end bell, and an outer cylinder of a canned motor pump, including: a connection cylinder having a through hole extending from the sealed space toward the external equipment; a cylindrical body mounted to the through hole of the connection cylinder to form a gap and a width of an explosion-proof gap; and a base joint that connects the connection cylinder to the sealed space, wherein one end of the connection cylinder is connected to the canned motor pump through the base joint connected to the sealed space, the other end of the connection cylinder is connected to the external equipment through a joint connected to the external equipment, and the connection cylinder having the through hole has a structure to resist an inner pressure generated by leaking handled fluid or gas by receiving the cylindrical body from the sealed space side. 
     Also, in the pressure-resistant explosion-proof connector according to the present invention, the other end of the connection cylinder is hermetically sealed by the external equipment. According to this structure, a pressure-resistant explosion-proof structure formed therein is terminated at the connection cylinder, so that there is an advantage that the external equipment such as a sensor is not required to be pressure-resistant explosion-proof equipment with a special structure and specifications. 
     Also, the external equipment connected to the pressure-resistant explosion-proof connector according to the present invention intends to detect the handled liquid leaking into the sealed space of the stator portion, and can detect damage to the can by detecting a pressure change in the stator portion or a volatile gas component by use of a pressure sensor, a gas sensor, a temperature sensor or the like. 
     Also, in the pressure-resistant explosion-proof connector according to the present invention, a threaded groove is formed in the through hole of the connection cylinder, the cylindrical body has a countersunk head screw portion, and the countersunk head screw portion of the cylindrical body is accommodated in the connection cylinder in close contact with an end surface of the connection cylinder. According to this structure, for example, even when the countersunk head screw portion is damaged by internal explosion, the cylindrical body blocks the through hole of the connection cylinder, so that an impact on the external equipment can be reduced. 
     Also, in the pressure-resistant explosion-proof connector according to the present invention, the connection cylinder is fixed to the base joint by engaging means for engagement. Example of the engaging means include a knock pin and a calking tool. By using such engaging means, it is possible to prevent loosening between the connection cylinder and the base joint and separation thereof due to internal explosion. 
     Also, in the pressure-resistant explosion-proof connector according to the present invention, the base joint is formed on a side surface of a terminal flange that connects the canned motor pump and a terminal portion. 
     Moreover, in the pressure-resistant explosion-proof connector according to the present invention, the base joint is formed on one of an upper surface, a side surface and a bottom surface of the outer cylinder of the canned motor pump. The base joint may be located at a position at least in communication with the sealed space of the stator, and preferably at a position where pipes and lines are easily installed. 
     By using the present invention, even a different type of sensor can be mounted via a common connector, to thereby eliminate the need for replacement of a connector including a mounting base for each sensor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a perspective drawing of a canned motor pump to which a pressure-resistant explosion-proof connector according to an embodiment of the present invention is mounted. 
         FIG. 1B  is an enlarged drawing of the pressure-resistant explosion-proof connector shown in  FIG. 1A . 
         FIG. 2  is a sectional drawing of the canned motor pump to which the pressure-resistant explosion-proof connector according to the embodiment of the present invention is mounted. 
         FIG. 3  is a sectional drawing of the pressure-resistant explosion-proof connector according to the embodiment of the present invention. 
         FIG. 4A  is an explanatory drawing for explaining a constituent component of the pressure-resistant explosion-proof connector according to the embodiment of the present invention. 
         FIG. 4B  is an explanatory drawing for explaining a constituent component of the pressure-resistant explosion-proof connector according to the embodiment of the present invention. 
         FIG. 4C  is an explanatory drawing of a constituent component of the pressure-resistant explosion-proof connector according to the embodiment of the present invention. 
         FIG. 5  is an explanatory drawing for explaining a gap of the pressure-resistant explosion-proof connector shown in  FIG. 3 . 
         FIG. 6  is an explanatory drawing for explaining mounting positions of the pressure-resistant explosion-proof connector. 
         FIG. 7  is an explanatory drawing for explaining a pressure switch provided in a terminal box of a conventional canned motor pump. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     In the following, a best mode for carrying out the present invention (referred to as embodiment below) will be described by reference to the drawings. 
       FIG. 1A  shows a canned motor pump  10  to which a pressure-resistant explosion-proof connector is mounted, and a pressure-resistant explosion-proof connector  20 . The canned motor pump  10  includes a centrifugal pump  11 , a stand  12  that supports a body, a motor  13 , a bearing holder  14  of the motor  13 , a terminal flange  15  mounted to an outer cylinder of the motor  13 , a terminal box  16  mounted onto the terminal flange  15 , a motor monitoring unit  17  mounted onto the terminal box  16 , and the pressure-resistant explosion-proof connector  20  mounted to the terminal flange  15 . A display window  18  that displays a bearing state is also provided in the motor monitoring unit  17 . The canned motor pump  10  sucks a handled liquid from a front direction of the centrifugal pump  11 , and discharges the handled liquid upward. Since the handled liquid is also circulated inside the motor, a drain screw  19  that allows the handled liquid inside the pump casing and the motor to be discharged is provided on a lower side of the centrifugal pump  11 . 
     The pressure-resistant explosion-proof connector  20  shown in  FIG. 1B  includes a base joint  21  mounted to the terminal flange  15 , and a connection cylinder  22  connected to the base joint  21 , and a pressure sensor  23  is connected to the connection cylinder  22 . A cable  24  extends from the pressure sensor  23  (strain gauge type). A knock pin  25  (for fixing and for preventing loosening) is also provided on the pressure-resistant explosion-proof connector  20  so as to prevent the connection cylinder  22  from being detached from the base joint  21 . Next, a liquid leaking state of the canned motor pump  10  will be described by using  FIG. 2 . 
       FIG. 2  shows a section of the canned motor pump  10  to which the pressure-resistant explosion-proof connector  20  is mounted. In the canned motor pump  10 , the centrifugal pump  11  and the motor  13  are connected to each other via a connection plate  33 , a can  28  covers an inner portion of a stator  38  of the motor  13  that drives the centrifugal pump  11 , and a region including the inside of the centrifugal pump  11 , the connection plate  33 , a sliding bearing  35 , 40  provided at the connection plate  33 , and a sliding bearing  35 , 40  provided at the bearing holder  14  is filled with the handled liquid, so that a rotating portion of the pump is filled with the handled liquid. Accordingly, a shaft portion  36  that separates an impeller  32  and a rotor  37  does not need to be sealed, and a structure where the shaft  36  is supported only by the sliding bearing  40  is obtained. The handled liquid discharged by the impeller  32  is discharged from the centrifugal pump  11 , and also used as a lubricating liquid of the sliding bearing  40  and a cooling liquid of the rotor  37 . 
     Since the stator  38  is hermetically sealed by the can  28 , the motor outer cylinder and end bells  34  and  41 , a sealed space is formed in the stator portion  38 , so that when the can  28  is damaged, the liquid leakage  29  does not occur outside and the liquid remains inside the stator. Also, due to a relationship between an inner pressure of the sealed space and a liquid pressure of the handled liquid, air inside the stator is released into the handled liquid, or the handled liquid flows out into the sealed space. Thus, when the can  28  is damaged, very small pressure variation occurs inside the sealed space. In the present embodiment, an electrical pressure sensor is provided via the pressure-resistant explosion-proof connector  20 , so that even the very small pressure variation inside the can  28  can be detected, and the damage to the can  28  can be detected at an early stage. 
     In another embodiment, a semiconductor gas sensor is connected via the pressure-resistant explosion-proof connector  20 . In the used semiconductor type gas sensor, tin oxide or the like that absorbs oxygen constitutes a porous body, and a gas concentration is measured based on a change in electric properties such as electric resistance caused when the absorbed oxygen is consumed by a reducing substance (methane, isobutane or the like). A crystal oscillation type gas sensor that detects gas based on a change in frequency of an oscillator caused when a chemical substance is attached to an oscillation surface, or a gas sensor that uses a surface acoustic wave, may be also used. By using such sensors, the damage to the can  28  can be detected at an earlier stage. 
       FIG. 3  is a sectional view of the pressure-resistant explosion-proof connector  20 . The pressure-resistant explosion-proof connector  20  includes the base joint  21  mounted to the terminal flange  15 , the connection cylinder  22  connected to the base joint  21  by a threaded portion  42 , and the knock pin  25 , and a aforementioned gas sensor is connected to the distal end of the connection cylinder  22 , through which gas is propagated, by a threaded portion  44 . Also, the connection cylinder  22  has a through hole therein, and accommodates a cylindrical body  26  connected thereto by a threaded portion  43 , to thereby form a gap and define a depth and width of an explosion-proof gap. The knock pin  25  is a pin for preventing loosening and decomposition to prevent the connection cylinder  22  from being detached from the base joint  21 . Next, the base joint  21 , the cylindrical body  26  and the connection cylinder  22  that constitute the pressure-resistant explosion-proof connector  20  will be described. 
       FIG. 4  show the constituent parts of the pressure-resistant explosion-proof connector  20 . The base joint  21  shown in  FIG. 4A  is fixed to the terminal flange  15  of the canned motor pump by welding or the like, and connected to the connection cylinder  22  shown in  FIG. 4C  by the threaded portion  42 . The through hole is also provided inside the connection cylinder  22 , and the cylindrical body  26  shown in  FIG. 4B  is connected to the through hole by the threaded portion. A male thread that allows the cylindrical body  26  to be screwed into the connection cylinder  22 , a slotted groove fitted with a slotted screwdriver for rotating the male thread, and a conduit  46  are provided in the cylindrical body  26 . An O-ring  27  that keeps an airtight connection with the base joint  21  is provided on a flange portion of the connection cylinder  22 , and the threaded portion  44  that connects the sensor is provided at the other end of the connection cylinder  22 . 
     One of features of the present embodiment is that a distal end of the through hole is formed in a tapered shape in the connection cylinder  22 , and the cylindrical body  26  is fitted into the connection cylinder  22  along a gas propagation direction. The through hole may be a through hole with a constant diameter, or a stepped through hole or a tapered through hole that can restrict movement of the cylindrical body. 
       FIG. 5  shows a depth (L) and a gap width (g) of the pressure-resistant explosion-proof connector  20  in  FIG. 3 . The construction requirements for explosive atmospheres set an interval and a depth of an explosion-proof gap in order to prevent a flame or spark from leaking outside. In the pressure-resistant explosion-proof connector  20  in the present embodiment, the depth (L) and the gap width (g) shown in  FIG. 5  are formed, and even when the threaded portion  43  and a close contact portion  45 , 47  are damaged, a distal end portion of the cylindrical body  26  abuts against a close contact portion  45 , 47  of the stepped through hole of the connection cylinder to stop gas propagation. With such a structure, pressure-resistant explosion-proof performance can be ensured even when the sensor connected to the other end of the connection cylinder  22  is replaced. 
       FIG. 6  shows plural examples of a mounting position of the pressure-resistant explosion-proof connector  20 . In the drawing, a pressure-resistant explosion-proof connector  20   a  is mounted to a side surface of the stator outer cylinder, a pressure-resistant explosion-proof connector  20   b  is mounted to a bottom surface of the stator outer cylinder, and a pressure-resistant explosion-proof connector  20   c  is mounted to an upper surface of the stator outer cylinder. Since the description regarding the canned motor pump  10  is similar to that in  FIG. 1 , the description regarding the canned motor pump  10  will be omitted. 
     In the canned motor pump  10  shown in  FIG. 6 , the pressure-resistant explosion-proof connector is provided not at the terminal flange  15  in the vicinity of the terminal box  16  to which the motor monitoring unit  17  is mounted, but at the outer cylinder of the stator. Generally, when leaking due to damage to the can, the handled liquid mostly remains in a lower portion of the stator. Thus, when the sensor is mounted to the upper side or the side surface of the stator outer cylinder below the terminal flange  15 , the liquid leakage can be detected at an early stage. 
     When the pressure-resistant explosion-proof connector  20   b  is provided on the bottom surface of the stator, the fluid leakage can not only be detected at an early stage, but a chemical substance leaking into the sealed space of the stator can also be discharged by removing the sensor from the pressure-resistant explosion-proof connector, and the leaking handled liquid can also be easily collected by arranging an oil pan below the pressure-resistant explosion-proof connector. 
     As described above, by using the pressure-resistant explosion-proof connector according to the present embodiment, even a different type of sensor can be mounted via the common connector, to thereby eliminate the need for replacement of a connector including a mounting base with respect to each sensor. Although the pressure-resistant explosion-proof connector is described by employing the canned motor pump as an example in the present embodiment, the present invention is not limited thereto, and it goes without saying that the present invention can be applied to other equipment.