fig1 illustrates an exemplary wellbore 10 that has been drilled through the earth 12 from the surface 14 down to a hydrocarbon - bearing formation 16 . the wellbore 10 has been lined with metallic casing 18 of a type known in the art . perforations 20 are disposed through the casing and into the formation 16 , thereby allowing hydrocarbons to enter the wellbore 10 . an electric submersible pump ( esp ) assembly , generally indicated at 22 , is shown disposed within the wellbore 10 by production tubing 24 . an annulus 26 is defined between the casing 18 and the production tubing 24 / esp 22 . the esp assembly 22 includes a pump section 28 , a seal section 30 and a motor section 32 . as is known , the motor section 32 drives the pump section 28 to draw hydrocarbon fluid in from the wellbore 10 via fluid inlets 34 and flow it to the surface 14 . a power cable 36 provides power to the motor section 32 from the surface 14 . as is known , the motor section 32 includes an outer housing , a stator and a rotor that is rotatable with respect to the stator . the rotor rotates a shaft that will , in turn , power the pump section 28 . it is noted that , while the motor section 32 and seal section 30 are shown in the drawings to be located below the pump section 28 , this is not necessarily the case in practice . the pump section 28 might be located below the motor section 32 . fig2 and 3 are cross - sectional views of portions of the interior of the seal section 30 . fig2 illustrates the upper axial end 38 of the exemplary seal section 30 having threaded openings 40 , which permit the seal section 30 to be affixed to the pump section 28 with suitable connectors ( not shown ). the outer housing 42 of the seal section 30 is made up of a top cap 44 , one or more outer housing sleeves 46 , and intermediate guides 48 , as are known in the art and which are typically threaded together . a central shaft 50 passes through the axial center of the housing 42 and , as is known , is used to transmit rotational power from the motor section 32 to the pump section 28 . a bellows chamber 52 is defined radially within each housing sleeve 46 . a well fluid chamber 54 is defined within the top cap 44 . mechanical seal assemblies , generally indicated at 56 , are disposed axially between each of the bellows chambers 52 as well as above the upper most bellows chamber 52 ( see fig2 ). those of skill in the art will understand that there may be a series of bellows chambers 52 and seal assemblies 56 within the seal section 30 , depending upon the needs and desires of the well operators . mechanical fluid seals 58 of known construction form part of each mechanical seal assembly 56 and surround the shaft 50 . a seal guide 60 is formed axially adjacent to and above mechanical seal 58 . portions of the seal assembly 56 reside within the seal guide 60 . a barrier fluid reservoir 62 is formed within each guide 60 and presents an open upper end 64 . barrier fluid 66 resides within each reservoir 62 . the barrier fluid 66 is a heavy specific gravity blocking fluid that is placed on top of the mechanical seal 58 to prevent well fluids from moving downwardly across the seal 58 and into the bellows chamber 52 below . the barrier fluid 66 can be a relatively heavy specific gravity fluid that does not mix well with water or other substances . in particular embodiments , the barrier fluid 66 has a density that is significantly greater than water . according to further particular embodiments , the barrier fluid 66 has a specific gravity that is from about 1 . 8 to about 2 . 2 . the purpose of the barrier fluid 66 is to displace and block water or well fluid from coming into contact with the rotating face of the mechanical seal 58 to prevent water or well fluid ingress past the seal assembly 56 . the barrier fluid 66 allows lighter fluids , such as lubricating fluid ( motor oil ) to pass upward through the barrier . a metallic bellows assembly , generally shown at 70 is located in each bellows chamber 52 and includes a radially outer bellows 72 , a radially inner bellows 74 and a sleeve 76 which interconnects the inner and outer bellows 74 , 72 . each of the bellows 72 , 74 is expandable and contractible axially in the manner of an accordion bellows . motor oil is retained within a bellows reservoir 77 that is formed by the bellows assembly 70 . the natural spring force of the bellows assembly 70 will tend to cause the motor oil to migrate up between the seals 58 and the shaft 50 , as illustrated by arrows 78 in fig2 and 3 . the barrier fluid 66 within the reservoir 77 will prevent well fluid from reaching the seals 58 , instead redirecting well fluids around the seal guide 60 and to exterior space 82 , as indicated by arrows 80 in fig2 and 3 . during typical operation , well fluid resides within the well fluid chamber 54 as well as the annular spaces 82 which radially surround the outer bellows 72 . well fluid may also enter the seal section 30 via port 84 . motor oil to be supplied to the adjacent motor section 32 is contained within each bellows assembly 70 . motor oil resides within each outer bellows 72 below the sleeve 76 and can be transmitted , under pressure , upwardly between the inner bellows 74 and the shaft 50 . also in accordance with particular embodiments of the present invention , biasing mechanisms are provided that produce positive fluid pressure within the seal section 30 and thereby dictate the preferred direction of leakage across the mechanical seals 58 of the seal section 30 and provide improved or even optimum pressure across the mechanical seal faces . fig2 depicts a biasing mechanism in the form of a weighted member 86 which is disposed within the outer housing 42 in order to exert pressure upon the motor oil within the bellows assembly 70 . provided the assembly is in the vertical position , the pressure applied will be proportional to the weight of the weighted member 86 . the pressure applied will largely not depend on the position of the bellows assembly 70 within the outer housing 42 . the weighted member 86 is preferably cylindrical and resides atop the sleeve 76 radially outside of the inner bellows 74 . in the depicted embodiment , o - ring seals 87 are compressed against sleeve 76 and help to hold the weighted member 86 in place as well as protect the bellows assembly 70 from potential damage from the weighted member 86 resulting from vibration . fig3 illustrates an alternative biasing mechanism for the bellows assembly 70 in the form of a compression spring 88 which urges the sleeve 76 axially downwardly . the compression spring 88 is shown compressed in fig3 . in this embodiment , the pressure applied to the motor oil within the bellows assembly 70 will be dependent upon the spring rate of the spring and the position of the bellows assembly 70 within the outer housing 42 . this pressure will be substantially unaffected by an orientation other than vertical in the wellbore 10 . those of skill in the art will recognize that numerous modifications and changes may be made to the exemplary designs and embodiments described herein and that the invention is limited only by the claims that follow and any equivalents thereof .