Centrifugal pitot pump with improved pitot

A centrifugal separator and pitot pump has a rotor driven in rotation within a casing with fluid to be cleansed of solid material entering a separation chamber of the rotor. Under a rotor imposed, centrifugal force field, solids in the fluid separate from the fluid and exit in a liquid carrier through a pitot tap close to the outer radial rotor wall. Radially interiorly of this tap, a pitot pickup intercepts cleansed production fluid and exits that fluid from the rotor. A head of a scoop of the pitot tap has an inlet in a blunt leading face and a top at the maximum radial limit of the scoop that is relieved from the leading face of the scoop to a trailing end. An inlet passage from the inlet generally parallels the line of the relief. In profile, the leading face of a scoop neck below the head curves in relief from the inlet face to a scoop base and has a relatively large radius of curvature. The leading face of the neck and base in planes normal to a radius from the axis of the rotor presents a blunt surface with curved transition corners between the middle of the face and the sides of the neck and base.

BACKGROUND OF THE INVENTION 
The present invention relates to centrifugal pumps of the pitot type and, 
more in particular, to an improved pitot pickup for such pumps that is 
particularly resistant to particle erosion. 
Centrifugal pumps of the pitot type are well known. In general, these pumps 
include a drive that drives a rotor in rotation within a casing. A pitot 
pickup in a chamber of the rotor is stationary relative to the rotor and 
intercepts fluid within the chamber and draws that fluid from the chamber. 
The exiting fluid has a head larger than its inlet fluid head because of 
energy imparted to it by the rotor. Typically, fluid enters the rotor 
chamber through an annulus surrounding a pitot tube mounting tube and 
through a plurality of radial passages in a rotor chamber cover to exit 
near the outer radial limit of the chamber. The pitot inlet in the chamber 
may be comparatively close to the outer radial limits of the chamber, or 
comparatively close to the axis of rotation of the rotor, or both, 
depending on the application. 
Centrifugal pumps of the pitot type find an application in petroleum 
recovery. Petroleum wells quite often employ downhole machinery to pump 
fluid produced by the well and fluid introduced into the well from the 
surface. These two fluids as pumped collectively are known as a power 
production fluid. The introduced fluid may be used to power downhole 
machinery. Typically, the downhole machinery is either a centrifugal or 
reciprocal engine. Power fluid for a downhole engine should be 
comparatively free of abrasives so that the engine is not damaged. For 
example, solid abrasives can erode journals and journal bearings of 
centrifugal machinery, in time erode blades of centrifugal machinery, and 
destroy seals in both types of machinery. Clearly, it is undesirable to 
subject downhole machinery to such a ruinous environment. Accordingly, 
attempts have been made to remove abrasives from the power fluid. 
The problem of abrasive removal from power fluid is a continuous one. The 
power fluid is typically oil recovered from the well and may be in an open 
system where power fluid is continuously generated from well fluid. Solid 
contaminants abound in well fluid. Even in closed systems where power 
fluid circulates in a closed loop, makeup fluid for the circuit brings 
into it abrasive solids, and inevitable contamination with abrasive solids 
occurs from other sources, such as contaminated lines and leakage. 
The well fluid may be multiple phase, having gas, oil and water content. 
Power fluid is usually single phase, either oil or water. 
Centrifugal pitot pumps, usually in conjunction with other separating 
equipment, have been used to remove solids from power fluid streams and to 
separate well fluid into its phases. One technique for solid removal uses 
the fact that the solids are denser than fluid and employs radial exit 
ports in the rotor through which the solid contaminants exit the rotor 
chamber. Agitation vanes may be used to prevent buildup and blockage of 
these radial ports. When used to separate production fluid into its 
phases, pickups at different radii for each phase draw such phases from 
the rotor. These pickups may be pitot tubes. 
The separation of solids from a production fluid stream through nozzles in 
the rotor of a pitot separator has disadvantages. When the casing outside 
the rotor is at atmospheric pressure, the fluid and solids entering the 
casing lose all their dynamic and pressure head. The fluid and solids in 
the typical case cannot be discharged into a collection vessel at the 
well. This discharge must, instead, be pumped away to some central 
collection area. The pump must typically raise the head of the solid and 
liquid discharge to several hundred pounds per square inch, say, 300 or 
400 p.s.i. Sometimes it is inconvenient to provide a pump for the 
discharge at the well. The head lost through the nozzles could have been 
used to introduce the solid and liquid discharge into a flow line. 
One system for separation of solids from production fluid employs a 
settling tank and a pitot separator. The settling tank effects phase 
separation by time and gravity. The pitot separator takes power fluid, say 
oil, from the separator and removes more solids from the stream. The pitot 
separator discharges separated solids and this fluid carrier back into the 
separator. The separator operates at flow line pressure so the discharge 
from the pitot separator does not suffer the large head loss that the 
alternative method entailed. However, the casing pressure of the pitot 
separator was necessarily high, and mechanical seal problems resulted. 
The pitot in the path of the rotating fluid within the chamber is subjected 
to the erosive effect of solids carried by the fluid. The erosive effect 
is directly proportional to the cube of the relative velocity between the 
fluid and the pitot. Particularly at comparatively large radii of the 
chamber, the erosive effect of the solids can be startling. 
Known pitot pumps includes those described in the following U.S. Pat. Nos. 
3,384,024; 3,776,658; 3,795,459; 3,817,659; 3,838,939; 3,926,534; 
3,960,319; 3,977,810; and 3,994,618. The pitot pickups of these patents 
are generally characterized by a head that extends forward toward oncoming 
fluid from a body. The entrance to the pitot pickup is in the head, and 
the material of the head surrounding the entrance may be sharp. The body 
below the head typically has a sharp leading edge. The surface of the head 
behind the entrance where cut by radial planes from the axis of the rotor 
is streamlined. 
SUMMARY OF THE INVENTION 
The present invention provides in a centrifugal pitot type pump an improved 
erosion resistant pitot scoop or pickup characterized by the combination 
of a blunt leading face surrounding the mouth or inlet to the scoop and a 
relief from the top of this leading face to the rear or trailing end of 
the head of the scoop. In a particular form, the invention provides a 
pitot scoop with this head, with the head extending upstream in a sense of 
rotor rotation from a body, and a neck of the body between the head and a 
base that in side elevation has a reentry curvature on its leading face of 
comparatively large radii of curvature. 
In a detailed form, the present invention contemplates a centrifugal pump 
of the pitot tube type that employs a rotor having a chamber within it and 
driven in rotation by some prime mover, such as an electric motor. The 
rotor is housed within a casing. A pitot tube pickup within the chamber 
has the scoop with the entrance to the scoop in the leading face thereof 
and facing opposite the direction of rotation of the rotor to intercept 
fluid. The scoop preferably is made of an erosive resistant material, such 
as sintered carbide, and is soldered onto a leg of the pitot that opens 
into an exit passage that is concentric with the axis of the rotor. Inlet 
fluid enters the chamber through an annulus between a pitot mount, 
preferably a tube or duct, and a plurality of radial passages in the rotor 
that extend from the annulus to an exit between the radial limits of the 
rotor chamber. Preferably, the scoop lies close to the outer radial 
periphery of the rotor chamber to intercept solids at their maximum 
concentration. A second scoop or pickup within the rotor chamber and 
radially closer to the axis of rotation of the rotor than the first scoop 
intercepts clean fluid within the rotor. This second pickup discharges its 
fluid into the duct that supports both the pickup and the scoop. A 
concentric line or duct within the tube draws off fluid and solid material 
collected by the first mentioned or outer scoop. 
Preferably, the scoop head for collecting solids has an inlet passage 
having an axis that at least approximately parallels the outer radial 
surface of the head. In one practical embodiment, this angle is about 
7.degree.. The outer radial surface of the head itself is slightly curved, 
with a comparatively large radius of curvature. The axis of the inlet 
passage continues from the entrance to join a radial passage that leads to 
discharge, preferably through the passage defined by the tube mentioned 
above. The entrance passage has an interior end with a spherical 
curvature. Diagonally from this end and at the inside corner between the 
entrance passage and the radial passage, a chamfered relief exists. The 
mouth of the inlet passage converges until it meets a cylindrical section 
of the inlet passage. As mentioned earlier, the leading face surrounding 
the mouth of the inlet is blunt. It can, in front elevation, resemble an 
octagon. A neck below the head and connecting the head to the base in 
side elevation has a reentrant curve connecting the base and the leading 
face of the head surrounding the mouth. This is a leading surface and it 
is also convexly curved in planes perpendicular to a radius of the rotor 
that falls within a central plane of the pitot tube. The flanks or sides 
of the head converge towards the posterior or trailing end of the head. 
The presently preferred form of the present invention has a pitot pickup 
assembly of both the dirty fluid pitot pickup and the clean fluid pitot 
pickup. As before, the scoop that intercepts dirty fluid has the unique 
configuration described. It mounts at the end of an arm that tapers 
radially outward in a major plane normal to the axis of rotation of the 
rotor. It also tapers radially outward in a plane containing that axis. 
The arm, in cross section normal to this radius, describes an elongated 
symmetrical outline with sharp leading and trailing edges. A tube of the 
assembly has an interior end, pocketed or notched to receive the base of 
the arm. The notch is V-cut to develop an interference between the arm and 
the duct. The arm preferably attaches to the duct by welding. At about the 
same axial position as the dirty fluid pickup, a clean fluid pickup formed 
integrally with the tube extends diametrically opposite the arm. It has 
been found that cleaning efficiency improves by reducing the axial extent 
of radial facing area of stationary objects in the rotor casing. This 
tube, as such, partakes a known configuration and has an arm portion with 
sharp trailing and leading edges capped by a tube-like head that resembles 
a section of a torus. A passage into this clean fluid pickup directly 
faces a circumferential component of fluid flowing in the rotor and 
proceeds from this entrance through a curved transition section into a 
radial passage that empties into an annulus formed in a tube of the 
assembly and which lies concentric with the axis of rotation of the rotor. 
A tube concentric with this axis and extending along it communicates the 
dirty fluid passage with an outlet. 
It has been found that with the construction of the scoop of the present 
invention that the life of the pitot tube has been materially increased in 
erosive environments. It is thought that the reason for the improvement in 
life lies in the control of fluid boundary layers about the pitot scoop 
that reduces the acceleration of particles that strike the scoop and 
therefore the erosive power of these particles. 
These and other features, aspects and advantages of the present invention 
will become more apparent from the following description, appended claims 
and drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
With reference initially to FIG. 1, an improved centrifugal pitot type pump 
and separator 10 is illustrated. A rotor assembly 12 mounts for rotation 
about an axis 14 within a casing assembly 16. A prime mover, not shown, 
such as a motor, drives the rotor assembly through a drive shaft 18. Fluid 
to be pumped and cleaned enters the pump through an inlet 20, in the 
direction of the arrowhead on the lead line for reference numeral 20, and 
passes into an antechamber 22. From this chamber the fluid passes down an 
annulus 24 towards rotor assembly 12. A plurality of radial passages 26 of 
the rotor assembly open into annulus 24. These passages empty fluid into 
an annulus 136 at their outer radial ends to empty into a rotor chamber 28 
with minimum turbulence. Rotation of the rotor assembly carries fluid in 
chamber 28 along with it. A pitot tube 30 within chamber 28 mounts on a 
duct or sleeve 32 that secures to casing 16. Pitot tube 30 includes a 
scoop or pickup 34 and a leg 36. An entrance 38 into scoop 34 faces fluid 
rotating in chamber 28 and draws this fluid from the chamber. The fluid 
passes into entrance 38, through the pitot tube, and along a passage 40 
within duct 32. Passage 40 is concentric with axis 14. The fluid exits out 
an outlet 42, as indicated by the flow arrow. 
A second pitot tube pickup 44 within chamber 28 and attached to duct 32 
intercepts solid material accumulating at the outer radial periphery of 
chamber 28. A head or scoop 46 at the outer radial end of pickup 44 
intercepts fluid and solids near this outer periphery and draws them off 
through a radial passage in the scoop and pickup and a line 47 within 
sleeve 32. 
Generally, then, fluid enters inlet 20 and passes through annulus 24 and 
passages 26 into chamber 28. Within passages 26, the head of the fluid 
increases. Within chamber 28 the fluid increases in head and stratifies 
according to its density, with the densest material being radially outward 
of less dense material. Solids, being the densest material, tend toward 
the outer radial wall of chamber 28 for exit collection by pickup 44 and 
removal from chamber 28. The solids, of course, are in a liquid carrier. 
Relatively clean, solid-free fluid leaves chamber 28 through pitot tube 30 
and passage 40. Solid material intercepting pitot head 46 can cause that 
head to erode. 
The erosion intensity of solids on an object struck by the solids is 
generally proportional to the cube of the velocity of the solid material 
with respect to the object. Since the velocity of the fluid within chamber 
28 increases as the radius, the erosive power of the solids suspended in 
the fluid increases generally as the cube of the radius of the rotor 
chamber. Around the entrances to the pitot tube scoops or pickups, it has 
been found that the erosive effect is substantial. The present invention 
provides an improvement in the resistance of pitot tube pickups or scoops 
to this erosion. 
With reference to Fig. 2, head or scoop 46 is shown in side elevational 
half section along the central plane of the scoop. The scoop head includes 
a base 50, a head 52, and a connecting neck 54. The base and neck together 
form a body. The scoop is one piece, preferably made out of sintered 
carbide. it has a radial, cylindrical passage 56 that opens into an 
entrance passage 58. Entrance passage 58 has an axis slightly oblique to 
the axis of passage 56. Entrance passage 58 has a mouth 60 of 
frusto-conical definition that diverges to an opening 62. Opening 62 is 
nearly cylindrical, but is slightly ovate. A blunt leading end face or 
surface 64 of the head bounds opening 62. As can be seen in FIG. 6, the 
outer perimeter of face 64 has a general octagonal configuration with the 
intersecting sides of the octagon rounded. The axis of passage 58 is 
indicated at reference numeral 68. The axis of passage 56 is indicated by 
reference numeral 70. Axes 68 and 70 intercept in this embodiment at an 
angle alpha of 97.degree.. Mouth 60 converges from leading end face 64 to 
a cylindrical passage section 72 of passage 58. A posterior end wall 74 of 
passage 58 has a spherical curvature with a radius of curvature 
corresponding to about the radius of cylindrical passage 72. Wall 74 
merges into the wall of passage 56. A relief 76 is on the inside corner of 
the junction between passages 56 and 58 and serves to attenuate erosion at 
this corner. 
Fluid and solids will enter mouth 60. Passing through passage 72, the 
velocity of the fluid increases slightly due to the decrease in 
cross-sectional area of the flow passage in the mouth. Fluid leaving mouth 
60 will then pass into and through passage 72 to turn the 83.degree. angle 
and head down passage 56 radially towards the outlet of the pump. 
A top surface 80 of head 52 representing the outer radial limits of the 
scoop is inclined at an angle to axis 70 of about 97.degree.. The outline 
of surface 80, however, is slightly rounded in planes radial with respect 
to the rotational axis of the rotor with a comparatively large radius of 
curvature. The curvature of surface 80 is mirrored in other external 
surfaces of the head, as can be seen in FIG. 3 and 7. 
The octagonal periphery of leading face 64 is indicated by reference 
numeral 86. This perimeter represents the beginning of the relief. The 
relief presented by surface 80, and the similar surfaces of head 52, from 
periphery 86 remove these surfaces from the backwash of the turbulence 
effected by the blunt nose of head 52 and thereby avoids the erosive 
effects of solids in this backwash. The edges of the octagon can be 
rounded. 
The provision of a blunt nose as the leading face of head 52 about entrance 
62 effects a substantial cushion of stagnant fluid between the leading 
face of the head and the fluid in rotor chamber 28. This cushion of 
stagnant fluid dampens the velocity of solid particles in their course 
towards the leading face of the head. Consequently, these particles lose 
energy and when they strike the leading face their erosive impact is 
reduced. The cushion also diverts solids from the leading face to follow 
stream lines that do not intercept the leading face. 
It has been found that the leading face of the scoop below the head is 
peculiary subject to the erosive effects of solids in the fluid in the 
rotor chamber. It has been found that these effects can be materially 
ameliorated by providing a reentrant or concave curved face 90 as the 
profile of the leading face of the neck in side elevation, as can be seen 
in FIG. 2. This reentrant curvature is formed of two circular arcs, with 
an upper arc having a radius slightly smaller than the radius of a lower 
arc. The reentrant curvature has large radii of curvature. The reentrant 
curvature sweeps downwardly from the lower portion of leading perimeter 86 
towards base 50 and rearwardly toward passage 56 to about the section line 
for FIG. 5, then comes back out again to terminate at a line 92. As seen 
in FIGS. 2 and 5, an apex 93 of line 92 falls on a line passing through 
face 64 that is also parallel with axis 70. With continued reference to 
FIG. 5, neck 54 has flanks 94 and 96. The reentrant profile of FIG. 2 is 
maintained in all planes parallel to the central plane of the FIG. 2 
section, but is somewhat softened by a fairing or rounding of leading face 
90 into the flanks of the neck. The fairing curves are convex and are 
shown at 100 and 102, respectively, in FIG. 5. As can be seen in FIG. 5, 
face 90 is blunt. Flanks 94 and 96 are generally parallel in the middle of 
scoop 46, but neck in slightly towards the trailing end of the scoop. 
It is believed that the provision of a reentrant curvature for the surface 
of the leading face of the neck effects a gradual deceleration of solid 
particles and a change in particle direction to soften the impact of the 
particles on the neck. 
In general, then, the rotation of the rotor about the scoop and the drawing 
of fluid by scoop 46 from within the rotor create a pressure depression at 
the entrance of the scoop that attracts fluid and particles. The resulting 
solid concentration tends to impact the scoop about its entrance with 
particles and to erode the scoop. In addition to this, the entrance to the 
scoop may be at a large radius. Consequently, the relative velocity 
between the particles and the scoop can be large and the erosive power of 
the particles large. The geometry of the scoop of the present invention 
minimizes the deleterious effect of the solid content in the fluid by 
reducing the kinetic energy of the solids and by diverting the solids away 
from the scoop. Diversion is effected by blunting the leading face of the 
head to create a thick layer of fluid in advance of the leading face that 
serves to dampen solids passing through it and to create a pressure field 
that diverts the solids away from the leading face. Vortices formed behind 
the leading face separate from the head in a short distance leaving a 
quiescent zone of fluid adjacent the head. Any solid materials entering 
this zone will have their kinetic energy substantially spent, thereby 
negating the erosive impact of this material. The leading face of the neck 
is removed from the entrance to the scoop to get the face out of the zone 
of influence of the entrance. The leading face of the neck is rounded to 
avoid the erosive effect that square corners experience. 
The generally octagonal shape of head 52 results from fabrication 
requirements of the material from which it is formed, sintered tungsten 
carbide. The tilting of axis 68 with respect to axis 70 maintains wall 
thickness between passage 72 and the outside of the head. 
With reference again to FIG. 1, scoop 34 attaches to leg 36 as by welding. 
Leg 36 conforms in general curvature to that of base 50 and therefore is 
rounded at its leading face. It contains a radial passage 120 that opens 
into passage 40. 
Pitot tube 44 attaches to sleeve 32 by a plurality of threaded fasteners 
122 between the base of the pitot tube and the sleeve. The pitot tube has 
a basal section 123 with a feathered leading edge 123 coextensive radially 
with the section. The feathered leading edge reduces drag. This edge of 
the pitot tube terminates at an outer radial limit well below the zone 
affected by a substantial density of solids, the outer radial limits of 
chamber 28 above scoop 46. An intermediate section 124 of pitot tube 44 
connects basal section 123 to scoop 46. Scoop 46 and intermediate section 
124 attach by a weld. A passage 126 in the pitot tube opens into an axial 
passage 128 of tube 47. Passage 128 lines on axis 14. Passage 126 extends 
radially of the rotor through sections 123 and 124 to open into passage 
56. Fluid and solids under pressure developed by the rotor pass through 
passages 126 and through passage 128 for collection or discharge into 
another line. In petroleum recovery, this line might be the flow line, and 
the cleansed fluid passing through pitot tube 30 could be used as power 
fluid for downhole machinery. 
Pitot tube 30 has scoop 34 capping leg 36 and attached to the leg as by 
welding. A mounting base 129 of pitot tube 30 opposite leg 36 provides for 
the attachment of pitot tube 44. 
The balance of the organization of the centrifugal pitot pump and separator 
of the present invention is generally known but will be presented here for 
completeness. 
Rotor 12 consists of a deeply dished rotor drum 132 that has a cover 133 
attached to it as by threaded fasteners 134. The interior of drum 132 and 
cover 133 define chamber 28. A urethane liner 135 on the inside wall of 
rotor 12 provides erosion resistance for the wall. Radial passages 26 
extend in cover 133 for a substantial proportion of the cover's extent and 
empty into an annulus 136 at their outer radial ends. This annulus empties 
into rotor chamber 28. The annulus has a cross-sectional area greater than 
the area of the radial passages and, accordingly, the velocity of the 
liquid entering the rotor chamber is reduced. Furthermore, the force of 
the liquid on pitot pickup 44 is continuous. The annulus 24 is within a 
hub 138 of the cover. A seal mating ring 140 has a nose 142 received in 
one end of hub 138. The mating ring couples to the hub as by dowels 144. 
Seal mating ring 140, away from the hub, bears against an axial interior 
end of a seal 146. O-rings between mating ring 140, hub 138 and seal 146 
prevent leakage along the interfaces between the seal mating ring on the 
one hand and the hub and seal on the other. 
Sleeve 32 forming the most for pitot tube 30 and pitot tube 44 itself 
mounts coaxially to axis 14 and extends concentrically with respect to 
seal 146 and retaining ring 140 to define the inner wall of annulus 24 in 
this axial region. The end of the sleeve remote from the pitot tube has an 
enlarged head 150 received in a cooperating bore of a drum end 152 of 
casing 16. A plurality of circularly arrayed screws 154 thread into 
cooperating female threads in head 150 to secure the sleeve to an 
extension 155 of drum end 152. A nipple 156 threads into the rear end of 
extension 155 and receives a T-fitting 158 containing outlet 42. A 
reducing bushing 160 in tee 158 receives a nipple 162. Tube 47 and bushing 
160 seal by an O-ring 164 between them. 
Drum end 152 includes extension 155. It also defines antechamber or annulus 
22 and a drain chamber 166. Antechamber 22 is bound by radial web 168 
between it and chamber 166, and, on an opposite radial wall, by an 
exterior wall 170. An axial, annular wall 172 bounds the outside of 
antechamber 22. As previously described, antechamber 22 opens into axial 
annulus 24 for the passage of fluid into the interior of the rotor for 
pumping the fluid. Chamber 166 receives leakage from a chamber 173 of 
casing assembly 16. A drain 178 into chamber 166 passes the leakage. 
Chamber 166 is bound on its radial inside by radial wall 180 and on its 
radial outside by web 168. An axially extending annular wall 182 bounds 
chamber 166 on its radial outside. 
A drum 190 of casing assembly 16 attaches to drum end 152 through a 
plurality of circularly arrayed bolts 192. A circular flange 194 locates 
drum end 152 on drum 190. Drum 190 has an axially extending annular wall 
196 that spans the axial distance of the rotor assembly, and a radial 
terminal wall 198 extending from this axial wall to a large axial hole 
200. A large radial wall or flange 202 of a pedestal 204 closes hole 200 
and attaches to wall 198 through a plurality of circularly arrayed bolts 
206. An end plate 208 attaches to wall 202 by screws 210 and forms a 
lubricant gallery 211 for a ball bearing 212. Bearing 212 provides a 
bearing support for drive shaft 18 proximate rotor assembly 12. A wave 
washer 214 between an annular, axially extending flange 216 of end plate 
208 and bearing 212 loads the bearing. The end plate and wave washer 
axially locate bearing 212. 
Pedestal 204 includes a sleeve 220 that receives drive shaft 18 and bearing 
212. It also receives a retainer ring 222 that has a conical bore that 
converges toward bearing 212. This shape directs lubricant thrown against 
the bore wall by rotating drive shaft 18 towards the bearing. Retainer 
ring 222 is located against bearing 212 by a compression spring 224 that 
bears at its opposite end on a second retainer ring 226. This retainer 
ring also has a conical bore to direct lubricant against another bearing 
228. Bearing 228 is for drive shaft 18. A grease gallery 230 between 
bearing 228 and a complementary bearing 232 provides lubrication for the 
two bearings. A lock nut 234 on threads of drive shaft 18 axially locates 
the bearings on the shaft in conjunction with a radial shoulder 236 of the 
shaft. Alemite fittings 238 and 240 provide the grease to galleries 230 
and 211. A spacer ring 242 and a lock nut 244 on drive shaft 18 locate 
bearing 212. 
Cover 250 attaches to the extreme end sleeve 220 as by bolts 252. A seal 
ring 254 seals the shaft interiorly of cover 250. 
Pedestal 204 has depending legs 256 and 258 for the mounting of the 
centrifugal pitot pump. 
Drive shaft 18, where it meets rotor assembly 12, has a radial flange 260. 
A plurality of circularly arrayed screws 262 bear on the flange and thread 
into drum 132 to secure the drive shaft to the drum. A nose 264 of drive 
shaft 18 pilots the drive shaft into the drum in cooperating stepped bore 
266 of the drum. A drain 270 from a collection annulus 272 drains 
lubricant from gallery 211. 
FIGS. 8 and 9 illustrate the presently preferred pitot pickups of the 
present invention. The pickups and attendant ducts interchange with the 
ones previously described and therefore the rotor assembly and casing 
assembly described earlier satisfactorily cooperate with the pitot tubes 
and ducts about to be described. A scoop 300, identical to scoop 46 
previously described, attaches onto the end of a radial arm 302. Radial 
arm 302 attaches by welding to a tube or sleeve 304 at an interior end 
thereof. The sleeve has a notch 306 receiving arm 302. The walls of the 
notch are welded to the arm. 
Arm 302 has a radial passage 316 that opens into a cooperating radial 
passage in scoop 300, which is identical to passage 56 of scoop 46. Scoop 
300 attaches to the outer radial end of arm 302 as by a brazed bond. The 
leading and trailing edges of arms 302 form a sharp knife edge. One of 
these edges is explicitly shown by a trailing edge 320 seen in FIG. 9. The 
surface of the arm fairs gradually from the leading and trailing edges to 
a maximum arm thickness midway between the edges. Thus the outline of a 
cross section of arm 302 normal to passage 316 outlines an elongate 
structure symmetrical about its major axis with a sharp, pointed end on 
its major axis. Arm 302 also tapers in both end side elevations from the 
base of the arm at notch 306 to it outer radial end. 
A stub section 322 of passage 316 opens into a passage 324 of a tube 326. 
Tube 326 lies on an axis 328 of tube 304. Passage 324 is concentric with 
axis 328. Tube 326 attaches to arm 302 by a weld. Tube 326 extends through 
tube 304. Tube 304 has an annular passage 330 concentric with axis 328 for 
its major extent. Passage 330, in the proximity of arm 302, turns 
gradually from axial to radial in a curved section 332. This section also 
decreases progressively in cross section. Transition passage 332 becomes 
primarily radial at 334. 
As seen in FIG. 8, tube 326 mounts to tube 304 at the end of tube 304 
opposite arm 302 by three radial ribs 336, 338 and 340. These ribs attach 
to the wall that defines passage 330 by a weld and to the outside of tube 
326 by welds. 
The location of scoop 300 in the rotor chamber typically is in a zone where 
the radial gradient of solid material is substantial. Accordingly, the 
outer radial end of arm 302 does not see much solid material. The arm can 
be shaped to minimize drag. 
The clean fluid take-off of this embodiment is shown at reference numeral 
346 and is of a standard configuration. It has a passage 348 that begins 
facing directly into the circumferential component of fluid flow. The 
passage continues basically circumferentially a short distance with 
gradually increasing cross-sectional area. The passage then turns radially 
inwardly through a transition passage 358 and into radial passage 334. 
Cross sections of pitot pickup 346 perpendicular to a radius from axis 328 
develop the elongate, streamlined surface configuration described with 
reference to arm 302. Thus, the leading and trailing edges of pitot pickup 
346, shown at reference numerals 350 and 352, respectively, are sharp 
edges. A head 354 of pickup 346 is generally in the form of a section of a 
torus. 
Tube 304 in external configuration is fundamentally the same as tube 32, 
with the exception of a seal ring 356. This ring serves to dissipate 
kinetic energy of a leakage stream from the rotor chamber into the inlet 
annulus and improves net positive suction head. The ring as such is the 
invention of another, and will not be further described. 
The pitot pickups of FIGS. 8 and 9 are about at the same axial location. 
This location avoids having both pickups in the path of particles moving 
radially outward in the rotor casing and improves the cleaning efficiency 
of the pumps. 
The present invention has been described with reference to a preferred 
embodiment. The spirit and scope of the appended claims should not, 
however, necessarily be limited to the foregoing description.