GB2110477A - Submersible motor having flexible diaphragm with check valve breather - Google Patents

Abstract

A submersible motor which comprises a casing containing a chamber having open ends includes a flexible diaphragm (66) sealing one of the open ends. The diaphragm flexes outwardly to accommodate the expansion of a motor fill oil within the chamber, and includes an integral check valve (20) which permits the fluid in which the motor is submersed to flow into the chamber in response to a pressure differential but prevents fluid from flowing out of the chamber. A guard surrounds the check valve and extends into the chamber farther than the check valve to prevent the check valve from engaging any parts of the motor. The guard includes radial passages which provide fluid communication between the volume inside the guard and the region outside the guard. A filter is positioned over the inlet to the check valve, received in a snap fit in an annular recess defined by a boss on the flexible diaphragm having a resilient inwardly extending flange. The flexible diaphragm includes a peripheral sealing bead (74) to prevent fluid from flowing around the periphery of the flexible diaphragm. <IMAGE>

Description

SPECIFICATION Submersible motor having flexible diaphragm with check valve breather Background of the invention Electric motors which are used with submersible pumps must be able to operate while submersed and subjected to considerable pressure from the surrounding liquid. One of the problems commonly associated with such submersible motors is the difficulty in providing a suitable system for lubricating the bearings of the motor and for keeping the motor running cool.

Most submersible pump manufacturers accomplish the lubrication and cooling by filling each motor, prior to sealing the motor, with motor fill oil between the stator and rotor in a chamber defined by the motor. In addition to lubricating the bearing surfaces of the rotor and its shaft and maintaining the motor temperature low during operation, the motor fill oil serves as a medium for antifreeze protection and corrosion prevention.

A persistent problem in assembling the motor has been the difficulty in completely filling the motor chamber with the motor fill oil. As a result, some air is usually present in the motor chamber when the motor is sealed. The presence of the air can lead to a pressure differential between the motor chamber and the fluid in which the motor is submersed, the differential causing an axial loading on the rotor shaft and a consequent loading on a thrust bearing engaged by one end of the rotor. As a result, it is difficult for the rotor to be turned and for the rotor to be started against the pressure exerted on the rotor through the thrust bearing by the pressure differential, especially since the pressure on the thrust bearing takes place when its bearing surfaces are stationary and subject to static friction.

Another problem that must be dealt with in connection with submersible motors is the expansion of the motor fill oil that occurs with increases in temperature. The motor fill oil is a mixture of water and about 5% propylene glycol, the mixture expanding at a greater rate than water alone. The expansion of the motor fill oil exerts pressure on the seals separating the motor chamber from the surrounding fluid and causes the oil to leak past the seals and out of the motor chamber. Expansion can occur when the motor is being stored at a high ambient temperature or during the operation of the motor when the rotor and stator temperatures increase in response to increased motor loads and currents.

It has been known in the prior art to provide a check valve for replacing motor fluid lost through the seals by allowing fluid to flow from the exterior of the motor chamber into the chamber.

U.S. Patent No. 3,777,194 to Schaefer et al, for example, mentions but does not illustrate a check valve permitting liquid to flow into but not out of the motor chamber. However, such prior check valves include a spring, a valve element and a valve seat, and they require drilling a hole through a part of the motor and performing other machining operations which add to the cost of producing the motor. The Schaefer et al patent also discloses a flexible diaphragm for equalizing pressure, but the diaphragm is separate from and not associated with the check valve. Thus the diaphragm is yet another part which is separately produced and must be separately assembled with the motor.

Summary of the invention It is, therefore, an object of the present invention to overcome the deficiencies of the prior art and to provide a submersible motor which includes a single member for preventing pressure differentials from developing between the motor chamber and the surrounding liquid by permitting liquid to flow from the exterior of the motor chamber to the interior and by accommodating expansion of the liquid within the chamber.

Toward the fulfillment of this and other other objects, the submersible motor according to the present invention includes a flexible diaphragm mounted over a bearing support member at one end of the rotor shaft to seal one end of the motor. The flexible diaphragm includes an integral duckbill check valve extending into the motor chamber for allowing fluid exterior to the motor chamber to flow in, thereby preventing pressure differentials from developing between the exterior and interior of the chamber. The flexible diaphragm flexes axially outward to accommodate expansion of the motor fill oil within the motor chamber, which occurs at high temperatures.A flanged annulus is defined on the exterior of the flexible diaphragm around the inlet to the duckbill check valve for receiving and retaining a sintered bronze filter in a snap fit for preventing foreign particles from entering the motor chamber. An upstanding spacer element surrounds the check valve on the interior of the flexible diaphragm and extends toward the bearing support to limit the movement of the flexible diaphragm toward the support and to maintain the check valve in spaced relationship with the end of the motor shaft.

Brief description of the drawings Fig. 1 is a cross-sectional view of a submersible motor according to the present invention; Fig. 2 is an enlarged cross-sectional view of a flexible diaphragm and a duckbill check valve in the submersible motor of Fig. 1; and Fig. 3 is a cross-sectional view taken along the line 3-3 in Fig. 2.

Detailed description of the preferred embodiment As is illustrated in Fig. 1, the submersible motor according to the present invention is generally designated by the reference numeral 10 and is arranged for connection to a suhmersible pump. The motor 10 includes a cylindrical stator 12 and a rotor 14 positioned within the stator 12 and secured to an axial shaft 1 6. The stator 12 is encircled by a sheet of metal, such as stainless steel, which defines the motor casing 18, and is engaged on its inner periphery by a sleeve 20, which, with the casing 18, defines a compartment for receiving the stator 12. The casing 1 8 and the sleeve 20 extend axially beyond the ends of the stator 1 2 and define grooves in which upper and lower end rings 24 and 26, respectively, are secured, such as by welding.

The shaft 1 6 extends beyond the stator 12 and the upper end ring 24 to define a splined end portion 28 for facilitating coupling to the pump.

Between the splined end portion 28 and the adjacent end of the motor 14, the shaft 1 6 extends through a journal bearing 30, made of a low friction material such as nylon or bronze, which is mounted within an upper bearing housing 32. The upper bearing housing 32 is received within an upper end cap 34 which'is secured to the end ring 24 by studs 36 or other suitable fastening means, thereby clamping the upper bearing housing 32 to the upper end ring 24. The upper bearing housing 32 defines a central cavity 37 having an open upper end and a counterbore 38 at the upper end to receive a lip seal 40 for engaging the shaft 1 6 to seal the upper bearing housing 32 from the ingress of the surrounding fluid.An O-ring 42 is positioned in a groove 44 defined on an exterior surface of the upper bearing housing 32 to provide a fluid seal in engagement with an inner annular surface of the end ring 24. A compression gasket 46 is provided between axially engaging surfaces of the upper bearing housing 32 and the upper end cap 34.

The shaft 1 6 terminates in a bottom end in a journal bearing 48 secured in a lower bearing housing 50 at approximately the same level as the bottom end ring 26. The lower bearing housing 50 also supports a thrust bearing 52 which is positioned between the lower bearing housing 50 and the lower end of the rotor 14 to absorb the axial thrust developed by the pumpmotor assembly. The lower bearing housing 50 includes a central cavity 54 and a radially extending flange 56 by which the lower bearing housing 50 is clamped against the lower end ring 26 by a lower end cap 58 secured to the lower end ring 26 by cap screws 60 or other suitable fastening devices.An O-ring 62 is received within a groove 64 defined in an exterior surface of the lower bearing housing 50, and a flexible diaphragm 66 is clamped over the central cavity 54 by the lower end cap 58 to seal the central cavity 54 from the liquid surrounding the submersible motor 10.

The sleeve 20 and the upper and lower bearing housings 32 and 50, together with the lip seal 40 and the flexible diaphragm 66, define a motor chamber, which includes the central cavities 37 and 54, as well as a main portion 68 extending axially in the submersible motor 10 generally between the upper and lower bearing housings 32 and 50 and between the rotor 14 and the sleeve 20. The motor chamber is filled as completely as possible with motor fill oil during assembly of the submersible motor. A radial port or ports 70 are provided in the upper bearing housing 32 to establish communication between the central cavity 37 and the main portion 68 of the motor chamber so that the motor fill oil can circulate from the main portion 68 and through the journalpearing 30 and the central cavity 37.

Similar ports 72 establish communication between the central cavity 54 in the lower bearing housing 50 and the main portion 68 of the motor chamber.

As is best illustrated in Fig. 2, the flexible diaphragm 66 comprises a disc of resilient material which includes an annular sealing bead 74 which is positioned in an annular groove 75 defined on an inner surface of the lower end cap 58 and is clamped between the groove 75 and an end surface of the lower bearing housing 50.

Thus, the annular sealing bead 74 acts as an integral O-ring, preventing fluid from flowing past the periphery of the flexible diaphragm 66. The lower end cap 58 defines a central well 76 in alignment with the flexible diaphragm 66 and in communication with the surrounding liquid by means of a passage 77 through the lower end cap 58. Thus, the pressure of the surrounding liquid is exerted on the bottom surface of the flexible diaphragm 66. A hollow annular ridge 78 of arcuate cross section is defined in the flexible diaphragm 66 to help provide the flexibility and freedom of movement necessary to permit the flexible diaphragm 66 to flex axially outward upon the expansion of the motor fill oil in the motor chamber.

As can be seen from Figs. 2 and 3, the flexible diaphragm 66 includes an integral resilient flattened conical formation extending axially inward into the chamber from a central portion and defining a duckbill check valve 80. The flattened conical shape of the duckbill check valve 80, together with a linear slit 82 at the end of a pair of converging flattened sides 84 and the resiliency of the material of the duckbill check valve 80, permits fluid to flow from the well 76 into the motor chamber under the influence of a small pressure difference, such as 1 psi. The duckbill check valve 80 prevents flow from the interior of the motor chamber to the well 76. A check valve guard in the form of a castellated circular formation 86 surrounds the duckbill check valve 80 and extends from a central portion of the flexible diaphragm 66 axially inward beyond the duckbill check valve 80. The formation 86 engages the lower end of the lower bearing housing 50 when the pressure in the surrounding liquid exceeds the pressure in the motor chamber, thereby limiting the axially inward movement of the flexible diaphragm 66 and maintaining the duckbill check valve 80 in spaced relation with respect to the end of the shaft 16. Radial passages such as grooves 88 are defined on the axial inner surface of the formation 86 so that the volume within the formation is in communication with the region outside the formation and with the ports 72, even when the circular formation 86 engages the lower end of the lower bearing housing 50.

In order to prevent the ingress of foreign particles into the motor chamber, a filter disc 90 of sintered bronze is received across the inlet to the duckbill check valve 80 in a snap fit within an annular recess 92 defined on an exterior surface of the flexible diaphragm around the inlet to the duckbill check valve 80. The snap engagement occurs between the periphery of the filter disc 90 and a radially inward extending flange 94 on an annular boss 96 surrounding the inlet to the duckbill check valve 80 and extending axially outward from the flexible diaphragm 66.The axially interior periphery 97 of the filter disc 90 and the central edge 98 of the flange 94 are bevelled to enable the filter dics 90 to cam the flange 94 outwardly, deforming the flange 94 until the filter disc 90 is in position in the annular recess 92, at which point the flange 94 snaps inwardly, retaining the filter disc 90.

When the submersible motor 10 is being assembled, the motor is inverted and the motor compartment is fillled as completely as possible with motor fill oil, the filling taking place through the duckbill check valve 80. When the submersible motor is installed and is submersed in liquid, the liquid enters the well 76 in the lower end cap 58 through the passage 77 and exerts pressure on the flexible diaphragm 66. If the motor chamber is not completely filled, air will be present and a pressure differential will exist across the flexible diaphragm 66. If this pressure differential were not relieved, the higher pressure of the surrounding liquid would exert a downward force on the upper end of the shaft 1 6 greater than the upward force exerted on the lower end of the shaft 1 6 by the lower pressure in the motor chamber.The net downward force which would result would cause the engaging surfaces of the thrust bearing 52 to bind due to static friction thereby making the motor difficult or impossible to start and resulting in early failure of the motor.

Therefore, in the motor according to the present invention, when the pressure of the surrounding liquid begins to exceed the pressure in the motor chamber, the circular formation 86 engages a surface of the lower bearing housing 50 and prevents the duckbill check valve 80 from hitting the end of the shaft 16 while the pressure differential exists. At the same time, liquid flows into the motor chamber through the filter disc 90 and the duckbill check valve 80 until the pressure inside the motor chamber is substantially equal to the pressure outside the motor chamber. The radial grooves 88 permit the entering liquid to flow from the volume within the circular formation 86 through the ports 72. Once the liquid has entered the motor chamber, it is retained by the duckbill check valve 80. If the pressure inside the motor chamber exceeds the pressure outside the motor chamber as the result of, for example, expansion of the motor fill oil due to increased temperature, the flexible diaphragm 66 will move away from the motor compartment and into the well 76, thereby lowering the pressure inside the motor compartment.

Although a specific illustrative embodiment according to the present invention has been described in the foregoing specification, it is understood that various changes and modifications may be made without departing from the spirit and scope of the present invention as recited in the appended claims and their legal equivalents.

Claims (11)

Claims

1. A submersible motor comprising: a casing containing a chamber having open ends; a stator and a rotor positioned within the casing; and means for sealing the open ends of the chamber, the sealing means including a flexible diaphragm having means for permitting fluid to flow past the diaphragm in one direction in response to a difference in pressure across the flexible diaphragm and for preventing fluid from flowing past the diaphragm in the opposite direction.

2. The submersible motor of claim 1 wherein the means for permitting fluid to flow comprises a check valve.

3. The submersible motor of claim 2 wherein the check valve comprises a resilient formation extending into said chamber and having converging sides which are biased toward one another to engage one another by the resilience of the formation, the sides being separable by said difference in pressure in said one direction but not by said difference in pressure in said opposite direction.

4. The submersible motor of claim 3 wherein the flexible diaphragm and the resilient formation together comprise one piece.

5. The submersible motor of claim 2 wherein the check valve extends into the chamber and a guard extends from the flexible diaphragm farther into the chamber than the check valve to prevent the check valve from engaging other parts of the motor.

6. The submersible motor of claim 5 wherein the guard surrounds the check valve and includes radial passages, so that the volume within the guard is always in fluid communication with the region outside the guard.

7. The submersible motor of claim 2 wherein a filter is positioned across the inlet to the check valve.

8. The submersible motor of claim 7 wherein a boss on the flexible diaphragm surrounds the inlet to the check valve and includes an inwardly extending resilient flange to define an annular recess, and the filter has a periphery larger than the periphery of the flange but smaller than the periphery of the boss, whereby the filter is received in the annular recess in a snap fit.

9. The submersible motor of claim 1 wherein the flexible diaphragm includes a hollow annular ridge.

10. The submersible motor of claim 1 wherein the flexible diaphragm includes a peripheral sealing bead.

11. A submersible motor substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.