FIG. 4 illustrates one embodiment of lower instrument sub 23, but the discussion is applicable also to upper instrument sub 33. Some of the numerals used in connection with FIGS. 1 and 2 are utilized in the discussion of FIG. 4 as those components are the same. In this example, intake member 25 is a separate member from lower instrument sub 23, but it could be integral with lower instrument sub housing 47. Intake member 25 is a tubular member with intake ports 60 formed in its side wall. The upper end of intake member 25 is threaded and secures to threads 62 formed in the inner diameter of housing 47. A bolt flange 61 formed  on  the  lower  end  of  intake  member  25 receives

threaded bolts for bolting intake member 25 to the upper end of seal section 21. Alternately, intake member 25 could have

a bolt flange (not shown) on its upper end that bolts to a bolt flange on the lower end of lower instrument sub 23. Also, intake member 25 could be located within a gas separator (not shown), or it could be within an upper portion of seal section 21.

A neck 63 of smaller diameter than the maximum outer diameter of housing 47 extends above housing 47 and has a bolt flange 65 for bolting with threaded fasteners or bolts 67 to a lower end of pump 27. Neck 63 could be a separate component secured by threads to internal threads in housing 47 in the same manner as intake member 25. Radial bearings

69 in housing 47 support shaft 51 radially and may be located adjacent both upper and lower ends of housing 47. Shaft 51 has splines 70 on its upper end that couple with splines on a shaft (not shown) in primary pump 27 via a spline coupling sleeve 72. Torque imposed on shaft 51 thus transmits to the shaft in primary pump 27. The lower end of shaft 51 also has splines 70 for engaging the shaft of seal section 21. There are various other arrangements for con- necting lower and upper instrument subs 23, 33 to primary pump 27. For example, union-type threaded sleeves as illustrated in U.S. Pat. No. 6,557,905, may be   employed.

Instrument sub housing 47 has at least one shoulder that is generally perpendicular to axis 51. In this example, sensor line port 46 is shown extending through an upward facing shoulder 71. Alternately, sensor line port 46 could extend through a downward facing shoulder in one or both of the instrument subs 23, 33.

Referring to FIG. 5, lower instrument sub 23 has a plurality of well fluid pump stages, and the number can vary, but will be much less than the pump stages of primary pump

27. The pump stages of lower instrument sub 23, as well as upper instrument sub 33 (FIG. 1), are preferably identical to those in primary pump 27, but they could differ. In this example, three dilllisers 73 are shown stacked on each other and secured against rotation within housing 47. Each dif- fuser 73 has a shroud 75 with a cylindrical outer diameter closely received in housing 47. Each diffuser has a hub 77 located within shroud 75 and spaced to define flow passages 79 that extend upward and  inward.

Two impellers 81 of are shown mated to two of the diffusers 73. In addition, an impeller (not shown) could be located above the top dillliser 73 and another below the bottom dillliser 75. Each impeller 81 has vanes 83 that extend upward and outward and define vane passages for imparting a higher velocity to well fluid received from the diffuser 73 directly below. FIGS. 4 and 5 show a mixed flow pump wherein the impeller vanes 83 extend upward out outward. This disclosure is also applicable to radial flow pump stages where the vanes extend primarily radially outward.

Impellers 81 are keyed to shaft 51 for rotation therewith. Normally, each impeller 81 is free to float axially a short distance on shaft 51. A down thrust washer 85 on each impeller 81 transfers downward directed thrust of each impeller to a mating down thrust washer on the dillliser shroud 75 immediately below. An up thrust washer 87 on each impeller 81 transfers upward directed thrust from each impeller 81 to a lower side of the dillliser hub 77 directly above.