Note: Descriptions are shown in the official language in which they were submitted.
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IMPROVED PUMP DRIVE HEAD WITH INTEGRATED STUFFING BOX AND CZAMP
The invention relates to an improved pump drive with integrated
stuffing box and clamp, i.e. a drive head for mounting at the top of
a crude oil well pipe for operating the pump installed in the well,
the pump being most commonly a positive displacement rotary design
having a progressing helical cavity.
Known in the prior art are a number of different drives arranged
to act on the ground surface end of the pump according to the well
delivery rate. Thus, constant delivery rate wells mount electric
motors connected drivingly to the pump shaft, the pump being as
mentioned most commonly a rotary positive displacement type with a
progressing helical cavity. Alternatively, a hydraulic motor is
provided with a variable ratio hydraulic drive for tracking the well
delivery rate up to steady state. The power transmission of the
1$ drive may include a gear or belt arrangement. In either case,
however, the pump is to be coupled to the drive somewhere above the
stuffing box, such that the interior of the well pipe, where the oil
pressure is that created by the pump or is the pressure of the well
itself, can be held isolated and the drive advantageously maintained
0 at atmospheric pressure. Finally, under the pulling force applied to
the drive shaft by a particular pump type, the transmission bearing
block must withstand high axial thrust forces.
Known in the art are several ways of arranging the components of
said head for easier servicing of parts that are more likely to
25 undergo wear or failure, such as stuffing box leakage due to
continual operation and the presence of silt deposits in the crude
oil, or possible thrust bearing failure under the axial force
exerted on the drive shaft by the pump. This involves periodical
servicing and daily monitoring, usually by a technician.
30 During such servicing, the pump in the well should be shut down
for the shortest possible time because, due to the mixed nature of
the fluid being pumped it can easily become clogged, resulting in a
costly well re-start procedure. Thus, quick replacement of parts is
of vital importance to a short-duration stoppage of the well pump
35 for service operations.
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Known is, e.g. from US Patent Application 2001/0050168 Al, a pump
drive head with an integrated stuffing box, wherein the stuffing box
locates above the rotary drive and uses an internal standpipe
attached to the coupling flange at the top of the well bore pipe.
Thus, motion transmitted through the drive is used for rotating a
tube mounted outside the stuffing box, since the coupling of the
drive to the pump shaft is placed above the components of the head.
The stuffing box, therefore, intervenes ' between the internal
standpipe and the outside tube connecting the drive to the coupling
of said tube to the pump inner shaft.
While by having the stuffing box placed on the top side of the
head, a technician can reach it more conveniently, the stuffing box
is difficult to check for tightness' because the seal is mounted
within a rotating part. The aforementioned patent application
teaches ways of pressurizing the seals from a suitable hydraulic
system to prevent .leakage and spilling onto the ground. However,
this involves significant complication over the conventional
arrangement of the stuffing box below the drive head, whereby the
extent of a failure can be checked visually by tapping the stuffing
box at different levels.
In addition, the dual function of the drive main bearings/pump
shaft thrust bearing invariably involves overhauling the whole
drive, rather than just the thrust bearing as the component most
subject to fail. Field disassembly of the drive requires more than
an hour, compared to the 20 to 40 minute time limit for the well
shutdown.
Finally, for the operation to be performed in less time,
something has to be done to make the clamps on the underside of the
wellhead a more practical design. To~ lock the pump driveshaft, a
radial clamp means is closed around the shaft by means of two screws
operated from outside. The aforementioned patent application
illustrates a few designs for this means. The technician, before he
can act on the head, locks the shaft in order to prevent it from
dropping down the well; therefore, having to operate two screws may
lead unskilled or careless personnel to torque one screw more than
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the other and cause the shaft to bend or become damaged.
The prior art is open to considerable improvement in the way of
providing the head with a pump drive which can obviate the above
deficiencies and make the servicing procedures faster to complete
and more effective in a reliable manner.
In the light of the foregoing, the underlying technical problem
of the invention is to provide a pump drive head, the stuffing box
and/or thrust bearing of which can be readily replaced without the
drive having to be disassembled in the field, and while still using
the conventional checking method of tapping at different levels.
Another object is to allow for both standard and packing-type seals
to be replaced the same way. Not least an object is to provide a
clamp of simple construction to effectively hold the~rotary shaft
locked during servicing operations.
The above technical problem is solved by the invention providing
an improved pump drive head having.an integrated stuffing box and
comprising: a power transmission coupled to the rotating pump
driveshaft within a crude oil well; a stuffing box to retain the
pressure; a thrust assembly adapted to take the tensile force
exerted on said pump shaft; characterized in that said power
transmission comprises a tube arranged to be rotated coaxially with
the shaft and having at least two different diameters; that the
rotary seals fit over the small outside diameter of the tube to
establish fluid-tightness between said tube and the body of the
stuffing box, the outside diameter of the seals being smaller than
the large outside diameter of said tube; that the tube-to-shaft fit
incorporates static seals; and that the rotating and static seals
are adapted, by virtue of a retainer ring provided, to come away
along with said tube and the component parts associated with the
seals inside said stuffing box.
In a preferred embodiment, the tube, being rotated coaxially with
the shaft, is connected with.its bottom end axially to a sleeve for
rotation therewith and to jointly define said large and small
diameters, the small diameter locating inside the stuffing box and
the tube and sleeve, once connected together, forming a unitary
3
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piece.
In another preferred embodiment, a gasket is provided on the
bottom end of said tube/sleeve for rotation therewith, the outside
diameter of the gasket being a labyrinth pattern.
In another preferred embodiment, wherein the rotary seals are
packing seals, an oil seal is provided downstream of the rotary
seals and of the inlet hole for the liquid lubricant to the packing;
the packing being mounted between said tube/rotating sleeve and the
inner seat of the stuffing box.
In another embodiment, the packing is mounted on said rotating
sleeve through at least one detent ring and a pre-load spring
between the packing and said retainer ring.
In another embodiment, the packing is mounted around the small
diameter of said tube/rotating sleeve and is held there by at least
one axial retainer ring and a pre-load spring placed between the
packing and the axial thrust assembly.
In another embodiment, the static seals are placed for reduced
radial bulk in the joint region between said tube and said sleeve,
and are compressed there to make a tight seal as said tube and
sleeve are made fast together.
In another preferred embodiment, the static seals are placed for
convenient replacement in the joint region between said tube and the
shaft, and make a tight fit within the skirt of the top cover.
In another preferred embodiment, said tube is connected to the
thrust assembly for rotation therewith by a rotating hub held in
place by a guiding tighten-down means.
In another preferred embodiment, said hub is formed on its inside
diameter with an axial slot for pulling out the connection tongue
between said tube and the drive.
In another preferred embodiment, the packing pre-loading spring
in the stuffing box is disposed inside a split casing to prevent
overloading the spring when in the compressed state.
In another preferred embodiment, a ring spacer is provided in the
stuffing box which is bored for communication with the liquid
lubricant inlet hole and is formed with an annular seat for a lip
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type oil seal arranged to contact the diameter of said tube/sleeve.
In another embodiment, said bored ring spacer is formed with an
axial middle ledge for insertion past the lip of an adjacent ring
seal.
In another embodiment, a gasket with a labyrinth pattern on its
inside diameter is keyed to the bottom end of the sleeve for
rotation therewith.
In another preferred embodiment, a shaft locking clamp,
advantageously placed within the body of the stuffing box, comprises
a jaw pair, one pulls and one pushes, operated through a screw
arranged to act with its end on one jaw and engaged in a threaded
hole formed in the other jaw; said push and pull jaws being operated
through a screw arranged to act with its end on the push jaw and
engaged in a threaded hole formed in the pull jaw.
In another preferred embodiment, a clamp with ,self-centering jaws
is associated with the body of the stuffing box, the jaws gripping
the shaft in a wedge contact relationship of the outer surfaces of
the jaws to the inner surface of the sliding body of the clamp under
the action of the tighten-down screw; advantageously, this wedge
contact is achieved by provision of a conical surface taper.
In a further preferred embodiment, the radial gripping movement
of the self-centering jaws is guided by a prismatic fit of the clamp
on the box or the cover; an elastic means is mounted between the two
jaws to open them when the clamping action is released;
advantageously, the shaft-gripping surfaces are semicircular about a
center that is offset from the shaft centerline in a direction
toward the opposite jaw.
One possible embodiment of the invention is shown by way of
example in the accompanying ten drawing sheets, in which: Figure 1
is a longitudinal section view of the improved head according to the
invention, showing the overall configurations of the stuffing box,
drive (here a gear power transmission), thrust bearing, and camp
for locking the pump driveshaft; Figure ~ is a partial enlarged view
limited to the rotating bearings of the drive, thrust bearing, and
stuffing box; Figure 3 is a vertical cross-section view of the self-
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centering clamp for locking the pump driveshaft; Figure 4 is a
sectional plan view of the clamp of the preceding Figure; Figure 5
is a longitudinal section view of the improved head, with an
unspecified drive, showing the overall configurations of the
stuffing box, thrust bearing, and clamp for locking the pump
driveshaft; Figure 6 is an enlarged detail view of the head shown in
Figure 5; Figure 7 is a sectional view of the stuffing box
highlighting the' packing mount; Figure 8 is a sectional view of
another embodiment of the improved head incorporating a modification
of the stuffing box and the self-centering clamp; Figure 9 is an
enlarged sectional view of the shaft power drive and the stuffing
box; Figure 10 is an enlarged sectional view of the self-centering
jaw clamp 'for the rotating shaft; and Figure 11 is a sectional plan
view of the clamp shown in the preceding Figure, with one of the
jaws being shown in section.
In Figure 1, the wellhead 1 is shown to include the drive 2 with
gears 3, 4 that are driven by the motor M, the gear 4 being keyed to
a rotating tube 5 connected upwardly to the thrust assembly 6 and,
through the conventional coupling 7, to the rotating driveshaft 8 of
the pump down the well bore. Also, the stuffing box 9 is shown
beneath the drive 2 and as being advantageously integrated here to
the self-centering clamp 10 with jaws for locking the shaft 8.
Figure 2 shows in greater detail the main bearings 11 for the
gear wheel 4 on the housing 12 of the drive 2. The rotating tube 5
is keyed to the gear wheel 4 by the tongue 13 and extends coaxially
within the gear wheel 4. The bottom end 14 of the tube 5 is threaded
at 15 for engagement with the rotating sleeve 16 of the stuffing
box. Static ring seals 17 are held compressed between said end 14
and the sleeve 16, these being the parts that would bear on the
rings during rotation. The rotating sleeve 16 of the stuffing box
carries the axial thrust bearing 18 arranged, inside the body 19 of
said box, to take the axial load from the well pressure acting on
the seals 20. Engaged threadably with the bottom end 21 of said
rotating sleeve 16 is the retainer ring 22 arranged to retain said
seals and used for pulling them off, the seals being shown held
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apart by spacers 23 that abut against said thrust bearing 18. A
rubber gasket 24 is connected to the retainer ring 22 which is
formed with a peripheral labyrinth pattern 25 on its outside
diameter to catch as much as possible of the solids trapped in the
pumped fluid. A radial tapping hole 26 is formed above the gasket 24
and at each oil seal 20 for use, when required, to check the
respective upstream seal for leakage under the well pressure.
Also in Figure 2, said tube 5 is shown connected rotatably to the
hub 27 of the thrust bearing, to which it is fastened together with
the top cover 28 by the screws 29. This hub can rotate under the
bell 30 covering the bearing 31 of the thrust assembly 6, and has an
upper oil seal 32. This bell is fastened to the housing 12 of the
drive 2 by screws 33. Said hub 27 is formed with an axial slot 34 on
its inside diameter to allow the tongue 13 to be pulled away without
the thrust assembly 6, i.e. the hub 27, bell ~30 and bearing 31
having to be disassembled.
Figure 3 shows the pull and push jaws 35 and 36 around the
outside diameter of the shaft 8. For enhanced grip, the contact
areas are knurled horizontally as at 37. The jaw pair are closed by
the outside-operated screw 38, which screw is provided with a seal
39 around its stem 40 to stop leakage of pressurized fluid. The
female threadway is formed on the body of the pull jaw 35, and the
end of the screw 41 acts on the push jaw 36. In Figure 3, the clamp
10 is shown open, and is shown closed in Figure 4. For guiding and
elastic bias purposes, at least two pins 43 and two springs 44 are
placed between the pull jaw 35 and the cover 42, which are effective
to keep the jaws from turning and bias them to the open position.
Shown in Figure 5 is the head for the power transmission 45 to
the shaft of the pump 8 of a crude oil well, when the head is
constructed other than from gears, e.g. comprises a pulley (not
shown) keyed to the tube 46 by the tongue 47'to rotate with the
tube. The thrust assembly 6 is provided with a hub 48, similar to
the hub 27 described above but formed with no axial slot. This
thrust assembly, having to take radial forces on said tube 46 as
3S well, additionally includes a radial bearing 49 and the sleeve 16 of
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the stuffing box 9. Figure 6 shows in further detail the stuffing
box with the oil seals 20 and intervening rings 23, and the static
seals 17 held tight on said shaft 8 by the end 14 of the tube 46. It
can be seen that the hub 48 guides the sleeve 16 of the stuffing
box, and above this, said tube 46. In this it differs from the
embodiment shown in Figure 2, wherein the sleeve 16 of the stuffing
box and the tube 5 are guided on the hub of the gear wheel 4.
Furthermore, Figure 7 shows the bottom end 21 of said rotating
sleeve 16 engaged threadably with the ring 22 to retain said packing
50, itself located between said sleeve and the inner seat 51 of the
,stuffing box 9. The packing is retained on said sleeve by the
retainer ring 22, the detent rings 52 and spring 53 against said
' axial thrust bearing 18. A bored ring spacer 54 and an oil seal 55
are provided between the packing 50 and said bearing 18. Said inner
seat 51 has a shoulder 56 for abutment by the ring 52 in the
assembled state. The spring 53 is to pre-load the packing 50, and in
the assembled state, the ring 22 will be held spaced apart from the
bottom detent ring 52. The tapping holes 57, where provided, are
covered by the packing 50. The hole 58 is to admit lube oil to the
inside diameter of the packing as this is sliding across the outer
'surface of said rotating sleeve 16. ~n possible collapsing failure
of the packing 50, the well fluid would rise above the bearing 18
and overflow through the vent hole 59 at atmospheric pressure.
Another embodiment of the head is illustrated by Figures 8 to 11.
In Figure 8, there is shown the integrated stuffing box 60, where a
sleeve 61 is rotated rigidly with the shaft 8 in rubbing
relationship to the packing 50. This sleeve extends coaxially with
and is firmly coupled in sealed relationship to the tube 62 that
transfers the motion from the gear 4 to the coupling 7 via the skirt
63 of the cover 28. The static seals 64 are placed between the cover
skirt and the shaft 8, so that the seals 64 can be readily pulled
off by first uncoupling the coupling 7 and removing the cover 28
with the skirt 63. Furthermore, the clamp 65 is shown located
beneath said integrated stuffing box with its self-centering jaws 66
closed by actuation of~ just the lead screw 67 and by effect of the
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conical fit 68 provided between the jaws and the sliding body 69.
Shown in Figure 9 is the body 12 of the head 1, whose upper
portion 70 receives the thrust assembly 6 mounted under the bell 71,
the latter being fastened by screws 72. The body 73 of the stuffing
box 60 is an integral part of the drive housing 12 and is formed
with tvao radial holes, of which the lower one 74 is located upstream
of the packing 50 same as the lowermost one of the holes 57, and the
upper one 75 same as hole 58, for supplying clean lube oil to the
rotary packing-type seal 50 acting on the outside diameter of the
sleeve 61. The gasket 76 with labyrinth 77, in static contact with
the shaft 8, is keyed to the bottom end of the sleeve 61 for
rotation therewith. Said bottom end of the sleeve also carries the
axial retainer ring 78 for pulling off the internal components of
the stuffing box 60. An axial retainer ring 79, being larger than
ring 78, is mounted between the lowermost packing 50 and an axial
ledge 80 on the body 73. Next to said packing is a casing split into
two halves 81 and 82 that are spaced apart to enclose the packing
pre-load spring 83. The casing contacts with its top portion the
ring 84, which ring is drilled radially to provide a passage for the
2~ pressurised tube oil from the hole 75. The bottom portion of this
ring is formed with an inner seat 8E receiving a rotary lip seal 86,
the top portion of the ring being formed with a middle, axially
extending ledge 87 for insertion between the outer metal shell and
the outer/inner lip of a seal ring 88 on the surface of said
rotating sleeve 61. This middle ledge 87 is to transfer a possible
axial thrust load directly to the axial thrust bearing 18. Last, an
isolating ring 89, provided for the thrust bearing 31, fits over the
outer diameters of the hub 27 and the hub of gear 11.
Figures 10 and 11, illustrating another embodiment of the self
centering clamp 65 for locking the shaft 8, show recesses 90
provided in the body 69 for the shaft 8 to go through during the
clamp-down operation. Each said self-centering jaw 66 is provided
with a pin 91 for guided movement in the slot 92 formed in the cover
93 of the clamp casing 94. Each jaw has a prismatic guide 95 that
lies normal to the direction of the jaw radial gripping movement,
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the guide tapering along the radial direction of the shaft 8. The
prismatic guide 95 fits for radial sliding movement in a circular
groove 96 cut in said cover 93, with the jaw being guided by said
pins 9l. Two springs 97 are received in sockets along a parallel
direction to the clamping direction to bias the jaws 66 to the open
position upon removal of the clamp-down force. A socket 98 is
provided in the area of the screw 67 on the body 69 to allow the
screw head through, and rotation-preventing pins 99 ensure an
orientated setting of the body 69 within the casing 94. The shaft-
gripping surfaces 100 are semicircular about a center which is
offset toward the opposite jaw with respect to the centerline of ,
shaft 8, and are slightly roughened with circular cross-section
knurled formations. '
The wellhead and drive disassembling/re-assembling for servicing
is effected, 'upon the shaft 8 being .stopped from rotating, by
operating the screw 38 to close the clamp 10 such that its jaws 35,
36 will grip the shaft; the jaws self-centering themselves around
the shaft without damaging it. Once the shaft is clamped down and
the well pressure exhausted, a conventional device is used for
loosening the coupling 7 and releasing the connection between the
shaft 8 and the rotating tube 5 or 46. By removing the screws 29 and
cover 28, the sleeve 16, static seals 17 and oil seals 20 of the
stuffing box 9 can be slipped off for quick replacement. In the
embodiment of Figure 2, the tongue 13 would not interfere with
removal of the tube 5 because of the slot 34 provided in the hub 27.
Replacement of the tube assembly 5 or 46, sleeve 16 with the static
seals 17, bearing 18, rotary seals 20, oil seals or packing,
retainer ring 22, and gasket 24 is quickly effected for a minimum of
well shutdown. Assembly would proceed in the reverse order.
To also take down the thrust assembly 6, by loosening .the screws
33 the thrust bearing 32 is released. Where both the stuffing box
and thrust assembly are to be replaced, by merely loosening the
screws 33 the thrust assembly 6 and stuffing box assembly can be
removed in a single, readily performed operation. In this respect,
the embodiments of Figure 2 and Figure 6 would be dealt with in a
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slightly different manner from each other, namely the gear
transmission 2 would remain connected to the body 19 of the stuffing
box 9, as would the respective bearings 11, and the bearing 49
removed together with the thrust assembly 6 and the inner parts of
the stuffing box 9.
Finally, the holes 26, in addition to being useful to tap off
leakage past the oil seal 20 or the gasket 24 located upstream, may
be used to introduce fluid, advantageously oil, under a pressure in
order to enhance the sealing action of the affected oil seal 20, the
pressure being propagated to the next oil seals in the direction
toward the thrust bearing 18.
When the packing 50 is employed, the ring 22 would be retaining
the packing 50' and detent rings 52 for assembling. For
disassembling, the ring 22, by acting against said detent rings 52
and the fully compressed spring 53, would urge the compressed
_ packing against the inner wall 51 of the box 9 and loosen it, thus
allowing it to be removed as a whole.
In the embodiment of Figures 8 and 9, the stuffing box operates
as explained here below. Upon assembly, the packing 50 would be
forced by the spring 83 against the axial retainer ring 79 and ledge
80; the packing being compressed between the outside diameter of the
rotating sleeve 61 and the bore in the body 73. The sleeve turns
together with the shaft 8 and the gasket 76 with labyrinth 77 to
stop slime in the crude oil being lifted from reaching, under the
pressure, the static seals 64 between the shaft 8 and the sleeve 63
at the top end of the head. The additional axial retainer ring 78 is
utilized as the packing and internal components of the stuffing box
60 are taken out; it functions as an axial retainer to prevent
components from coming off. The split casing 81, 82 allows the
spring ~o preload the packing at the same time as it prevents
overloading the spring 83 should the backpressure of the clean oil
outflowing from the hole 75 vanish while in operation. In the last-
mentioned case, the axial thrust would be transferred from the
packing 5 to the casing, and thence directly to the ring 84; from
3$ this ring, it would be further propagated to the axial thrust
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bearing 18 via the axial middle ledge 87. Thus, the thrust force
would leave the lip seal 86 unaffected and free to cling firmly; nor
would it affect the seal ring 88, because the axial middle ledge 87
transfers the thrust directly to that portion of the seal ring which
is strongest in the axial direction. The ring 88 stops the clean
lube oil from entering the upper chamber outside the stuffing box
60, and the lip seal or oil seal 86 allows the clean lube oil from
the hole 75 to flow through, but prevents clean oil and'crude oil
from flowing back to the bored ring 84. The lip or oil seal 86 would
not wear out, because in general, well pressure only makes itself
felt while the shaft is held stationary. In operation, the clean
Tube oil to the packing is admitted through the hole 75 and
distributed between said seal ring 88 and the packing 50 to also
fill the annular chamber inside the split casing 81, 82. The lube
oil pressure is maintained above the well pressure to prevent
dripping past the packing to the head, so that the dripping is
conveyed into the well and the contact between the packing and the
sleeve 61 can be kept in a suitable condition for proper performance
and a long life.
For.servicing, the hole 74 is used for draining the stuffing box
60 before disassembly, thereby avoiding undesirable splashes as may
foul the thrust bearing 31 and besmear the operator. In addition,
said hole allows the stuffing box 60 to be flushed clean with its
internal components and the packing in place before the well is re-
2,5 started .
The shaft locking clamp 65 with its self-centering jaws 66 is
operated by first tightening down the screw 67 to urge the clamp
body 69 in a radial direction of the shaft 8 against the jaws 66 and
cause the latter to close around the shaft 8 along normal directions
to the body direction of displacement. The contact between the body
and the j aws occurs across the inside taper 68 of 'the body and the
mating outside taper of the jaws 66. The jaws will be guided in
their movement toward each other by the taper 68, the prismatic
guide 95, and the pins 91 in the slot 92. At the end of the clamp-
down step, the springs 97 will move the jaws 66 away as the body 69
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is pushed back by turning the screw 67 in the opposite direction.
Advantages of this invention are that: by having the stuffing box
9 mounted below the thrust assembly 6 and the drive components, full
operational control of the rotating seals 20 or 50 and the gasket 24
is achieved; by having the thrust assembly planed at the top, with
the inner components of the stuffing box 9 removable through the
top, replacement is quickly effected with only a very short well
shutdown; the operator can thus maintain a comprehensive stock of
spare parts that may include the thrust assembly 6, and directly
replace any worn out or failed items in a wellhead.
,In practicing the invention, the materials used, the dimensions
and construction details may be other than those described
hereinabove, yet be technical equivalents thereof, without departing
from the juridical domain of the present invention. The tube
62/sleeve 61 combination could be manufactured as a unit, although
this would entail a more complicated construction and be cost-
intensive.
Thus, the clamp 10 or analogously. the clamp 65 could be provided,
although less conveniently, as an independent unit rather than as an
attachment to the body 19 of the stuffing box 9.
'An unrelated construction, as provided by the invention, of the
stuffing box 9 to the thrust assembly 6, although feasible, would be
less convenient. In fact, the more readily damaged items in use
would be the seals between rotating parts, oil seals or packings,
2$ thrust bearing 31, and static seals 17 and 64. A separate
construction, although feasible, would impair simultaneous quick
replaceability of the parts when damaged, the rotating seals 20 or
50, the thrust assembly 6, and the gasket 24. On the other hand, the
shaft locking clamp 10 or 65 could be a separate construction,
unlike that shown in Figures 1, 5 and 8 having the clamp integral
;vith the body of the stuffing box.
13
