US3854064A

US3854064A - Mechanical seal isolator

Info

Publication number: US3854064A
Application number: US00358921A
Authority: US
Inventors: C Dunbar
Original assignee: TRW Inc
Current assignee: Northrop Grumman Space and Mission Systems Corp
Priority date: 1973-05-10
Filing date: 1973-05-10
Publication date: 1974-12-10
Anticipated expiration: 1991-12-10

Abstract

A mechanical seal isolator is provided in a submergible pump installation for protecting a mechanical seal from well fluid. The mechanical seal, which prevents well fluid from passing along a shaft to an oil-filled electric motor, may be located at the top of an oil-containing motor protector which is positioned between the pump and the motor or at the top of the motor itself. The mechanical seal isolator is interposed between the seal to be protected and the pump and contains a fluid of greater density than the well fluid and the oil in the protector or the motor and of sufficient quantity to surround and extend over the mechanical seal under all operating conditions of the motor.

Description

United States Patent 1191 Dunbar MECHAPHCAL SEAL ISOLA TOR Clarence E. Dunbar, Bartlesville, Okla.

TRW, Inc., Cleveland, Ohio Inventor:

73 I Assignee:

1451 Dec. 10,1974

Primar Eramirrrr-l D. .\liller Assistant Examiner-Harpy E. Moose. Jr. Attorney, Agent, or Firm-Shapiro and Shapiro [57] ABSTRACT A mechanical seal isolator is provided in a submergible pump installation for protecting a mechanical seal from well fluid. The mechanical seal, which prevents well fluid from passing along a shaft to an oil-filled electric motor, may be located at the top of an oilcontaining motor protector which is positioned between the pump and the motor or at the top of the motor itself. The mechanical seal isolator is interposed between the seal to be protected and the pump and contains a fluid of greater density than the well fluid and the oil in the protector or the motor and of sufficient quantity to surround and extend over the mechanical seal under all operating conditions of the motor.

8 Claims, 2 Drawing Figures PAIEMEB EM T 3.854.064

' SHEET 10F 2 FIG? PATENTEU 2 1 3354.064

1 SHEEI 2 0F '2 F/GI 2 1 MECHANICAL SEAL ISOLATOR BACKGROUND OF THE INVENTION This invention relates to submergible pump installations and is more particularly concerned with the protection of a mechanical seal which prevents well fluid from passing along a shaft to the driving motor.

'In the art of submergible pumps, which may be em ployed to pump oil or water from a well, for example, it'is common practice to employ a pump of the centrifugal type driven by an electric motor filled with oil which lubricates and cools the motor. Since the oil in the motor expands and contracts, depending upon whether the motor is operating or at rest, it is also common practice to provide a motor protector of the oilfilled. type between the motor, and the pump or of the breathing bag type in the motor to accommodate the expansion and to prevent the ingress of corrosive well fluid to the motor when the oil contracts. In a protector of the oil-filled type, an-arr'angement of chambers and passages keeps an interface between the oil and the well fluid out of the electric motor. In the breather bag type of protector, a collapsible diaphragm may be built into the lower end of the 'motor 'to accommodate changes in volume of the oil in the motor; As long as the oil is not lost or contaminated and the mechanical seal on the shaft leading from the motor remains intact, well fluid is kept out of the motor. Oil-filled electric motors, motor protectors, and related apparatus are disclosed, for example, inthe following U.S. patents:

REZtJ,783 2,674,702

1,701,468 2,739,252 2,979,347 l,970,484 2,740,058 3.l l6,432 2.236.887. 2,783,400 3,l53.l60 2.270.666 2,854,595 3,384,769 2,674,194 2,922,055 3,502,9l9

In U.S. Pat. No. Re. 26,783 and in U.S. Pat. No. 3,502,919 it is proposed to employ in a motor'protector a so-called intermediate'fluid between the ambient well fluid and the motor oil, the intermediate fluid having a higher'specific gravity than theambient well fluid and the motor oil and serving'to separate the well fluid from themotor oil in a manner intendedto prevent contamination of the motor oil by the well fluid. However, a serious problem which has continued to exist in the prior art is that under conditions of normal operation the mechanical seal which is located at the top of the protector (or which is at the top of the motor, where a breather bag is used) 'and which is intended to prevent the passage-of well fluid to'the motor along the shaft connecting the pump andth emotor is exposed to the well fluid and hence is subject to corrosive and abrasive attack by the well fluid. The life of the me.- chanicalsealand the lifeof the electric motor itself are thus shortened, requiring that the entire pump installation be pulled from the well for repairs at an earlier time than would otherwise be the case.

SUMMARY OF THE INVENTION I It is accordingly apr incipal object of thepre sent' in vention f to provide a mechanical seal. isolator whichchanical seal isolator is interposed between the pump and a standard oil-filled motor protector, or between the pump and a motor having a breathing bag, without requiring modification of the pump, the protector, or the motor.

Still another object of the invention is to provide a mechanical seal isolator which maintains a body of high density fluid around and above the mechanical seal under all operating conditions of a submergible pump motor.

Briefly stated, in accordance with a first embodiment of the invention a mechanical seal isolator is provided between a standard oil-filled protector of an oil-filled electric motor and a submergible pump driven by the motor. The isolator includes a housing containing a shaft which connects the shaft of the motor protector with the shaft of the pump, the protector shaft also being connected to the shaft of the motor. The isolator contains a quantity of high density fluid sufficient to surround and extend above the mechanical seal at the top of the protector duringall operating conditions of the pump installation. A portion of the high density fluid extends into the motor protector also. Inaccordance with a second embodiment, the seal isolator is interposed between the pump and the motor and also maintains high density fluid around and over the sea] at the top of the motor shaft, which is coupled to the shaft of the isolator.

BRIEF DESCRIPTION OF THE DRAWINGS DETAILED DESCRIPTION OF THE INVENTION Referring to the drawings, and initially to FIG. 1, the invention will be described in its application to a submergible pump installation 10 comprising a submergible pump 12, an oil-filled electric motor 14, and an oilcontaining motor protector 16. Although only the right half of the figure is shown in section, for purposes of the explanation of the invention the left half may be assumed to be essentially the same. The pump may be a conventional centrifugal type, such as the pump disclosed in US. Pat. No. 2,270,666 or U.S. Pat. No. 2,775,945, for example. Similarly, the motor may be a conventional type, such as the motor disclosed in U.S. Pat. No. 2,270,666 or U.S. Pat. No. 2,315,917, for example, and the protector may be a standard type employed with such a motor. For purposes of illustration ofthe principles of the invention, the protector may be assumed to be a protector of the type disclosed in U.S. Pat. No. 2,783,400. lnterposed'between the pump 12 and theprotector 16 is the mechanical seal isolator 18 of the invention. Y Y I The mechanical seal isolator comprisesa housing 20 which may be bolted or secured by'thre ads to the pump 12 at the upper end and-to the protector 16 at the lower end. As shown, the mechanical seal isolator has a pair of

bearings

22 and 24 adjacent to the opposite ends thereof for rotatably supporting a shaft section 26 along the axis of the isolator housing. The shaft is provided with

splined ends

28 and 30 which are coupled to similarly splined ends of corresponding shaft sections of the protector and the pump by means of couplings, one of which is shown at 32. The lower end 34 of the protector shaft section is similarly coupled to the upper end of a shaft section of the motor 14. It is apparent that when the components of the submergible pump installation have been assembled, a coaxial or colinear arrangement is provided of the general type disclosed in U.S. Pat. No. 2,315,917 or U.S. Pat. No. 2,775,945 (but without the mechanical seal isolator of the present invention).

The interior of the housing of the isolator provides a chamber 36 for containing fluid, and the spiders or

transverse partitions

38 and 40 which support the bearings of the shaft section 26 are provided with passages such as 42 and 44 for the fluid. A drain and fill valve 46 is provided for initial filling (or draining) of the chamber 36.

As shown, the motor protector has a conventional mechanical seal 48 located in a top portion of its housing, theseal surrounding its shaft section 50 adjacent to the upper end thereof. Such seals, which are well known in protectors of the type referred to, have been employed heretofore to prevent well fluid from passing along the shaft section 50 to the motor 14. If well fluid enters the motor, it is likely that serious damage to the motor will ensue because of the corrosive and/or abrasive nature of the well fluid. To repair this damage, it is necessary to pull the entire installation from the well. Although standard motor protectors will accommodate expansion of the oil in the motor which occurs when the motor operates and will normally contain a suffiwill eventually migrate along the shaft into the motor,

a highly undesirable condition, as stated.

In accordance with the present invention, the mechanical seal 48 is isolated from the well fluid, and protected from the deleterious effects of the well fluid, for all operating conditions of the motor, that is, whether the motor is runnning or at rest. Hence, the useful life of the mechanical seal is substantially lengthened. This is accomplished by providing in the chamber 36 a fluid of greater density and specific gravity than the well fluid and than the oil in the protector and in sufflcient quantity to be in surrounding contact with and to extend above mechanical seal 48 under all operating conditions of the motor. As described in U.S. Pat. No. 2,783,400, chamber 52 of the protector is filled with protector oil. When the oil in the motor expands, it forces oil along a'passage indicated at 54 surrounding the shaft section 50 to openings (not shown) into the chamber 52 at the upper end thereof, forcing oil' in the chamber 52 up a conduit 56 which extends from a point adjacent to the lower end of chamber 52 to the region of, the mechanical seal 48 (and preferably above the seal). In theabsence of the mechanical seal isolator of the invention, the oil in the protector will then move upwardly into the lower portion of the pump housing. However, when the motor has stopped running and the oil has contracted, well fluid will move downwardly from the pump housing into the region of the mechanical seal and into the conduit 56.

In accordance with the present invention, on the other hand, heavy duty fluid 58 from housing 20 surrounds and extends above sea] 48 at all times, filling the conduit 56 and the lower portion of chamber 52 in the protector at all times. This high density fluid 58, which may be Series E Freon (Dupont), for example, rises in chamber 52 of the protector to a level such as indicated by line 60 when the motor is idle, with concurrent lowering of the level of the high density fluid in chamber 36 of the isolator, as indicated by line 62. When the motor is running, the expansion of the oil in the motor and the protector forces the high density fluid in chamber 52 down, as indicated by line 64, and up in chamber 36, as indicated by line 66. It is thus apparent that the mechanical seal 48 is fully protected from contact with the well fluid. To prevent agitation of the heavy duty fluid in the chamber 36 a shaft tube 68 is employed, a thin layer of heavy duty fluid being present between the tube 68 and shaft section 26.

FIG. 2 illustrates a second embodiment of the invention, in which the mechanical seal isolator (essentially the same isolator described with reference to FIG. 1) is interposed between the pump 12' and the motor 14. The lower end 30 of the shaft section 26 of the isolator is coupled to the upper end of a shaft section 70 of the motor, while the upper end 72 of the shaft 26 is coupled to the lower end of shaft section 74 of the pump. The housing of the isolator 18 is bolted to the housing of the motor and the housing of the pump in the form shown.

The motor is a conventional type having a breathing bag or diaphragm 76 at the lower end thereof. Such motors are disclosed, for example, in U.S. Pat. Nos. 2,674,702; 2,974,240; and 2,979,347. A conventional mechanical seal 78 surrounds shaft section 70 at the top of the motor to prevent ingress of external fluid to the interior of the motor, which is filled with oil.

The pump 12', which may be of a conventional centrifugal type as noted previously, has a mechanical seal 80 surrounding the pump shaft section 74 to prevent well fluid from entering the interior of the lower chamber 82 of the pump housing, which contains a breathing diaphragm 84, one side of which is exposed to the well fluid, as is the case with diaphragm 76.

In the embodiment of FIG. 2, heavy duty fluid fills the chamber 36 of the isolator, fills the chamber 82 of the pump, and extends downwardly through passage 42 so as to surround the mechanical seal 78 at the top of the motor 14'. Thus, even if well fluid leaks past the seal 80, the mechanical seal 78 will be isolated from the well fluid by the heavy duty fluid, expansion and contraction of which is accommodated by the breathing diaphragm 84.

The mechanical seal isolator of the invention may be used with standard pumps, protectors, and motors without requiring modification of any of these components. The isolator allows normal operation of the mechanical seal and any pressure balancing means which may be present. The heavy duty fluid will surround the seal even if over expansion causes loss of most of the fluid. Moreover, the heavy duty fluid has higher heat transfer capabilities than the fluids which would otherwise contact the seal, further contributing to extended seal life.

While preferred embodiments of the invention have been shown and described, it will be apparent to those skilled in the art that changes can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims.

The invention claimed is:

1. In a submergible pump installation, a rotary pump having a pump shaft section, means including an oilfilled electric motor for driving said pump, said driving means having a shaft section provided with a mechanical seal for preventing the pumped fluid from passing therethrough to said motor, and a mechanical seal isolator comprising a housing interposed between said driving means and said pump and having a shaft section connecting said shaft section of said pump to said shaft section of said driving means, said housing having a chamber therein communicating with said seal adjacent to one end of the housing, said chamber containing a fluid of greater density than said fluid to be pumped and said oil, said greater density fluid being in surrounding contact with said mechanical seal under all operating conditions of said motor, irrespective of the expansion and contraction of the oil in said motor.

2. An installation in accordance with claim 1, wherein said chamber communicates with said pump adjacent to the end of the said housing which is opposite said one end.

3. An installation in accordance with claim 2, wherein said housing of said mechanical seal isolator has bearing means disposed adjacent to the ends thereof for supporting the associated shaft section coaxially therewith, said bearing means having fluid passages associated therewith for conducting fluid in said chamber past said bearing means, and said shaft section in said housing having coupling means at the ends thereof for coupling the last-mentioned shaft section to the shaft sections of said pump and said driving means, said housing having means for connecting the same to said pump and to said driving means.

4. An installation in accordance with claim 1, wherein said driving means comprises an oil-containing motor protector interposed between said motor and said isolator, said protector having a housing with said seal located in a top portion thereof, said protector having a chamber therein with an upper end below said seal, said protector having a conduit extending from a point above said seal to a point in said protector chamber adjacent to the lower end thereof and having a passage for introducing oil at a point in said protector chamber adjacent to the upper end thereof when the oil in said motor expands, said greater density fluid filling said conduit and occupying a portion of said protector chamber adjacent to said lower end.

5. An installation in accordance with claim 1, wherein said motor has a housing with said seal located in a top portion thereof, said seal isolator having the lower end of its housing connected to the upper end of the motor housing, said motor having breathing diaphragm means for accommodating expansion and contraction of the oil in said motor.

6. An installation in accordance with claim 5, said pump having a housing with a chamber at the lower end connected to the upper end of the seal isolator chamber and containing said greater density fluid.

7. An installation in accordance with claim 6, wherein said pump has breathing diaphragm means for accommodating expansion and contraction of said greater density fluid.

8. An installation in accordance with claim 1, wherein saidisolator has a tube surrounding the shaft section of said isolator to prevent agitation of said greater density fluid.

Claims

1. In a submergible pump installation, a rotary pump having a pump shaft section, means including an oil-filled electric motor for driving said pump, said driving means having a shaft section provided with a mechanical seal for preventing the pumped fluid from passing therethrough to said motor, and a mechanical seal isolator comprising a housing interposed between said driving means and said pump and having a shaft section connecting said shaft section of said pump to said shaft section of said driving means, said housing having a chamber therein communicating with said seal adjacent to one end of the housing, said chamber containing a fluid of greater density than said fluid to be pumped and said oil, said greater density fluid being in surrounding contact with said mechanical seal under all operating conditions of said motor, irrespective of the expansion and contractioN of the oil in said motor.

8. An installation in accordance with claim 1, wherein said isolator has a tube surrounding the shaft section of said isolator to prevent agitation of said greater density fluid.