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Патент USA US2108771

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Feb. 15,1938.
'
Y
J. P. LAIRD
FLUID PUMP
’
2,108,771
l
Filed Jan. 30, 1935
2` Sheets-Shoe?I 2
2,108,771
Patented Feb. 15, 1938
UNITED STATES
PATENT ‘ OFFICE .
2,108,711
FLUID PUMP
_
Joseph Paul Laird, Philadelphia, Pa., assignor to
The Wicaco Machine Corporation, Philadel- <
y phia, Pa., a corporation of Pennsylvania
Application January 30,l 1935, Serial No. 4,003
'7 claims. (o1. ros-126)
My invention relates to the art of .pumping
heavy 4oils and other relatively thick and viscous
of smaller capacity and having adjustment of
the capacity of the secondary pump by axial
movement of one of the gears and to facilitate
.
In a gear pump having adjustment of the 4leakage between opposite ends of the movable
5 rate of pumping by axial movement of' one of gear of the secondary -pump so as to permit
.
the gears to match Ia variable _part of its face easy shifting of the movable gear.
A further purpose is to provide primary and
against a corresponding part of the face of the
secondary gear pumps, one of them adjustable,
mating gear,`one purpose is to provide an equaliz
ing connection between the spaces at opposite within the same pumping unit, whereby con
10
10 ends of the adjustment movement so as to facili , veniently and with a high degree of space econo
m'y
pressure
may
be
maintained
between
the
tate flow of leakage liquid between the two spaces
two pumps, not only to supply the second pump
while the axial adjustment is being made. „
In the handling of heavy oils and like ñuids with fluid from the first but to add the pressure
fromthe primary to the pressure of the sec
which are pumped with difficulty, a further pur
15 pose is to increase the fluidity of the oil by the ondary, pump, making 'it possible to secure the
desired pressure from the secondary pump at _a
use of a primary pump in so close relation to a
secondary pump by which itis to be delivered low energy expenditure in the secondary pump.
A further purpose is to operate a two-stage
as to give little opportunity between for the oil to
gear pump with higher volumes pumped by the
increase in viscosity.
A
A further purpose‘is to break up and diffuse primary stage, and to continuously by-pass at a
20
selected pressure any excess of liquid pumped
and preferably at the same time raise the tem
perature of heavy oils and other olly viscous ma , by the primary pump back to the inlet side of the
'
terials pumped by a primary pump so as to primary pump.
In a two-stage gear pump, a further purpose
lower their viscosity and render them of substan
is to by-pass continuously at a predetermined 25
tially uniform viscosity when delivered to a sec
ondary pump whose pumping action is thus made pressure excess liquid pumped by the secondary
stage back to the conduit connecting the stages,
more nearly uniform.
A further purpose is to break up and diffuse a and, if necessary, from the conduit connecting
iiuids.
heavy substance or an accumulation in an oil or
30 other fluid pumped by a primary pump, there
by breaking up the "set” of the material pumped,
and to deliver it to a secondary pump before
the material has had opportunity to again be
come “set”.
,
A further purpose is to provide primary and
secondary gear pumps in series in a single unit
having the capacity of the first of the series
pumps in- excess of the normal capacity of the
second and having the capacity of the second
40 pump adjustable by axial movement of one of the
gears.
_
A further purpose is to interconnect primary
and secondary pumps within the same pumping
unit, of which the primary pump is designed to
45 have the larger pumping capacity and the sec
ondary pump is adjustable for quantity pumped,
the stages to the inlet of the primary stage.
The construction shown is a preferred con
struction only, selected because of its practica
bility and its excellence in illustration of the in
vention.
Figure 1 is a section through the axes of the
pumps- taken upon line I-l of Figure 2.
Figure 2 is a section upon line 2-2 of Figure 1.
Figure 3 is a fragmentary section correspond
ing generally to Figure 1 but upon a smaller
scale than that of Figure 1 and showing a sec
ond form of the invention.
l
‘
Figure 4 is 'a fragmentary section correspond
ing generally to Figure 2 but upon a smaller
scale than that yof Figure 2 and showing another
form of the invention.
'
`
Where gear pumps are operated at a relatively
high rate of`speed, such, for example, as 1750
so as to secure any desired pressure of -delivery -R. P. M., the tolerances or clearances between
..55
from the primary pump and varlable'rate of de
livery from the second pump.
A further purpose is to provide a primary gear
pump having capacity in excess of its .pumping
needs and having a short circuit connection
about the pump providing leakage against a
predeterminable preferably adjustable resist- '
ance, to pump from it to a secondary gear pump,
the gears and their surrounding casings may be
relatively large, because the speed of operation
is suiiicient to make the leakage through these
relatively large tolerances small enough to be
considered negligible in ordinary operation. On
the other hand, when pumps of this character
are greatly reduced in speed, (as for example
down to 200 R'. P, M.) it is necessary to operatev
40
2, 108,77 1
the pumps at very much closer tolerances or with it.I The piston 39 yis arcuately recessed to
I 2
clearances.
Á
With the axially adjustable gear type of pump,
where the adjustable gear unit is moved axially
to engage a larger or smaller proportion of the
gear faces of its mating gear for larger or smaller
pumping capacities, the spaces which must be
allowed at the ends of the gear unit to permit
movement of the unit axially become much more
10 tightly sealed than where larger clearances have
been provided.
These spaces soon ñll up with
leakage from the material pumped.
Whereas clearances> suitable for high speed
gear operation nave permitted leakage oil from
15 the end of the gear toward which adjustment is
being made to ñow out past the movable unit-and
into thespace at the end of the gear unit from
which movement is being made, allowing easy ad
justment, this pressure flow from the space at
20 one end of- the movable gear unit to the space at
the other end of the unit requires more and more
pressure with the smaller tolerances necessary
for lower speeds until with the tolerances which
correspond with and form a close fit with the
outer surfaces of the teeth of gear 2| and corre-
spondingly to Afit the-cylindrical surface 40 of
a cylindrical collar 4I which fills in the block or
body at this point. - 'I‘he collar isvof the samedi
ameter as the outside of the teeth of gear 2i.
The two pistons and the pump gear 22 between
them slide as a unit within a cylinder of uniform
diameter, into which project at one end and from
the side the surface of the collar 4I and the gear
2|. The teeth of the gear 2i mesh to varying
axial extents with the teeth of gear 22, as the
adjustable unit is moved to the right (Figure 1)
to cause deeper axial extent of meshing, and 15
hence higher pumping capacity, or to the- left
(Figure 1) to reduce theextent of meshing and a
lower pumping capacity.
The two pistons 38 and 39 are alike except for
the cylindrical recess of the piston 39 to corre
spond with and pass over the teeth of gear 22.
It will be noted that a portion of the cylindrical
surface of collar 39 projects into the cylinder
are desirable from other standpoints it becomes i Within which the pistons slide.
25 almost impossible to shift the gear without break
age. 'I'his difficulty is, of’course, very much in
creased with increase in viscosity of the fluid
pumped.
i
'
In any position of the two pistons between the
ends of their stroke there will be cylinder end
spaces 42 and 43 between the respective -pistons
and the ends 44 and 45 of the cylinder. `Inevi- .
~ One feature of the invention is intended to
tably the oil _which is being pumped will leak past
30 relieve this diñicultyin adjustment of the gear
the pistons 38 and 39'intopthe spaces 42 and 43
so that at any'time during the.--- operation of the
pumps the spaces 42 and 43 can be assumed to
be full of oil with corresponding interference with
movement of the adjustable pump unit.
Movement of the unit in either direction must
unit and others provide for primary pump supply
under pressure for a _gear pump secondary and
for the breaking'up and smoothing of the liquid
to be pumped, where its character or its ‘initial
35 temperature have given it a “set” making it dif
ñcult to pump smoothly and evenly until this
“set” has been broken up.
v'
10V
force theoil out of the space toward which the
pistons are moving in order'to make it possible
to move the pistons, at the same time tending to
The casing I0 is preferably made up as shown
of two generally ñat front and back plates or . cause a vacuum in the space at the opposite end
40 faces II, I2, secured by bolts I3 to an intervening '
block or body I4 within which the various gears
are mounted. The casing accommodates a pri
mary gear pump I5 and a secondary adjustable
gear pump I6. The primary pump is made up of „
of the movable unit. With relatively large tol
erances the diii‘lculty inmoving the pistons has
not- been a serious one, as the tolerances permit
the oil. to be forced back through the same chan
nels by which it reaches these spaces, but. with
driving gear I1 keyed tddrive shaft I8 and driven
gear I9 keyed to shaft 20. The secondary ad--
reduced speed of pump rotation and the co‘nse
justable gear pump is made up of drive gear 2l
flculty of moving the pistons becomes so great as
-and driven (adjustable) gear 22.
to be serious, threatening breakage of the parts.
>
For convenience of reference. the material
50 Dumped will hereafter be referred to as oil.
.40
quent necessity for reduced tolerances, this dii'
45.
In order to relieve from trapping of oil in spaces ,
42 and 43 a leakage passage 46 is provided, ter 50
The primary gear pump draws its oil through minating preferably in recesses 41 sumciently
any suitable pipe 23 leading from a .sump to the back of the line of the ends of the cylinders so
as not to be closed when the pistons are in their
suction side of the primary pump at 24 and trans
mits the oil through passages 25, 26and 21 to the extreme positions at either end of the stroke.
This leakage passage need have but very small 55
55 secondary gear pump, by which it is pumped
through passages 28 and 29 to'any suitable point capacity, since oil will not pass through it ex
cept when the movable pump gear unit is being
of discharge for use.
s The shaft'l8 is suitably driven as from a pulley shifted axially and there will -then be the pres
sure of the operating mechanism to shift the pis
8
60
Thev shaftA 20 is keyed to a driving gear 3l, one , tons and force leakage through from one space 60
of a transmission train which connects and syn
. 42 or 43 to the other. On the other hand, since
chronizes the two pumps. Gear 3| meshes with
leakage through this passage 46 can do Àno harm
at an time there is no objection to having the
an idler 32 mounted upon a pin-33 and the idler`
in turn drives a gear 34 which is keyed to a shaft
65
35. 'I_'he shaft 35 is 'keyed to the driving gear 2|
of the second (secondary) gear pump. . The gear
2l meshes- to different extents according to the
adjustment with the axially .adjustable driven
gear 22 mounted upon or about rod 36 and may
70 turn directly upon the rod or upon a bearing
sleeve 31 carried by the rod, as preferred.'I'he gear 22 and its bearing (if it bear upona
sleeve rather than upon the rod) is shifted lon
gitudinally as part of a unit comprising pistons
75
38 and 39, both pinned to the rod 36 and shiftable
resistance to flow through the passage 46 low. _
In order that the leakage throughpassage 46' 65
may provide the entire'oil transfer adjustment
needed with longitudinal movement of the gear
unit, the cross-sections perpendicular to the rod
36 must be equal in the spaces _42 and 43. This
can be accomplished readily by> making the rod 70
36 of such lsize that _its cross-_section equals’ the
cross-section by _which the cylindricalI portion 40
of the collar 4I projects into' -the cylinder. Ap
proximately equal cross sections are quite desir
able and are contemplated..
75
3
2, 108,771
The rod 35 is made axially adjustable by
threading it at 48 into an adjustment wheel 49
rotatably supported at 50 in a bracket 5I secured
_to the rear plate of the pump at 52. The adjust
5 ment wheel 49 is threaded at 53 to receive a nut
54 which holds the wheel 49 in position on the
bracket. 'I'he adjustment. wheel 49 is toothed at
space 42 to the opposite 43 or vice versa, allowing
free and easy movement of the secondary unit
parts.
-
i
The operation of over-pumping by the primary
as compared with the secondary will be deter
mined in large measure by the extent of inter
iitting of the gears of the secondary pair. With
adjustment of this secondary pair position fluid
55 to engage a spring detentr56 secured at 51 to
lthe bracket 5I. , The adjustment wheel 49 may be
10 -power driven if desired through engagement of a
in one or other of the spaces 42 and 43 is driven
interior parts between the spaces 42 and- 43. ' In
handling of various liquids, particularly liquids
rack with the teeth of the adjustment wheel.
Instead of the passage 46 through' the pump
body, a passage may be provided through the
15 Figure 3 I show a passage 46' through the rod 36,
and equalizing Vpressure between the spaces 42
and
43.
,
,
`
The rod 35 is protected and may be in part
supported by a gland 58 compressing packing 59
20 where the rod passes through the casing face I2.
The driving shaft I8 is also protected by a gland
shown at 6U, compressing packing -6I. It vhas
outboard bearing at 62 and 63 in the face Il of
the casing and in the body I4. Pin- 20 has bear
25 ing at 54 in the‘front face, at 65 in the body and
at 65 in the rear face.
The bearing of the pin 35 is at B9 in the body
30
of high viscosity such as oils and chemicals, for v15
example, viscose liquors. -Particularly in han
dling liquids of this type the feature of equaliz
ing pressure between two ends of the cylinder
containing the movable gear is of considerable
importance as is also the provision of pressure 20
relief for the primary and secondary pumping
stages.
It is likewise desirable in this ñeld to
pump a relatively larger volume by the primary
stage than that pumped by the secondary stage. ,
In view of my invention and disclosure, varia 25
tions and modifications to meet individual whim
or particular need will doubtless become evident
to others skilled in the art,- toobtain all or part
body and withinl the4 face plate I I. The bear-f
ingsl 62, 53, 64, v66,. 61, 68, 10 and 1I§are all out
board bearings, an'important feature in the con
thestructure shown, and I, therefore, claim all 30
of the benefits of my invention-without copying
such in so far as they fall within the reasonable .
spirit and scope of my invention'.
Having thus described my invention, rwhat I
and all of the pins `are provided with outboard
claim as new and desire to secure by Letters'
support.
Patent is:-
The primary pump is shown as of greater
capacity than the secondary pump in order that
there may be a full supply of ñuid for the sec
ondary pump and preferably also inl order that
40 the secondary pump supply may be under pres
sure so as -to increase the pressure of the dis
charge from the secondary pump.
In order that the primary pump may operate
continuously, an overflow is provided between the
45 _primary and secondary pumps which overflow is
preferably against an adjustable resistance. Two
types of overñow are shown, the one through pas
sages 13, 14 and 15 about the pump (Figure 2),
protected by anadjustable ball check valve 16
whose pressure is applied by a spring 11 bearing
50
against a seat 18 and adjustable by use of dif
ferent springs and different positions of the plug
19;-and the other through a pipe 80 (Figure 4)
to a pressure tank, not shown. The pipe 80 may
60
10
justment of the position of the movable gear unit
by operation of the adjusting wheel 49.
My novel pump finds wide application in the
and at 10 in the rear face; also at 1I in the collar
4I which in turn is supported at 12 within the
struction of the device, so that the driving shaft
35
to the other space, allowing free and easy ad
therefor, a driven pump gear upon said driven
shaft and meshing with`the driving pump gear,
a driving transmission gear driven from said
driven shaft, a driven transmission gear driven
from the driving transmission gear, a shaft and
bearings therefor, a driving secondary pump gear
mounted upon the driven transmission shaft, a
driven secondary pump gear adaptedA to mesh
with and be adjusted axially with respect to the 50
~driving secondary pump gear, walls forming a
cylinder fitting the driven'secondary pump gear,
pistons at opposite ends of the driven secondary
pump gear, movable inthe cylinder, one of them
having an arcuate opening to accommodate the
tank in which the mounting pressures check the
pumping effect of the primary pump.
The various passages about the pump are
drivenusecondary pump gear longitudinally, Walls
' The secondary pump has a by-pass relief simi
lar to that of the primary pump and comprising
passages 13', 14’ and 15', a ball check'valve 16',
spring 11’ (which is desirably heavier than spring
65 11), valve seat 18’_and plug 19’. Relief is thus
provided against excessive pressure von the deliv- -
‘ery-side ofthe secondary pump.
In operation the pumping effect of the second
ary pump isl adjusted by longitudinal movement
of the movable gear to mesh variantly according
to the position of the unit with the driving gear
of the secondary pumping pair. This alone is
broadly old.
'
- When the secondary gear adjustment is to be
75 eiïected the4 fluid pumped is driven from one
35
against leakage, a driving shaft, bearings there
for, a. driving primary pump gear on the'driving
shaft, a primary pump driven shaft, bearings
‘ lead through a check yvalve to the sump side of
the pump, as in the other case, \or to a pressure
closed,- by plugs 8l.
,
1. A gear pump comprising front and back
pump plates, a body between the plates, means for
connecting the plates againstv the body protecting '
driving secondary pump gear, a filler for the arcu
ate opening, means for shifting the pistons and
forming an inlet to the primary pump, an outlet
.from the secondary pump and a series connec 60
tion between the pumps, and the transmission
gearing betweenthe pumps being proportioned to
operate the secondary pump at a higher speed
than the primary pump. .
2. A gear pump comprising front and back 65
pux?p plates, a body between the p1ates,»rneans
for connecting the plates, against the body pro
tecting against leakage, a drivingl shaft, bearingstherefor, ‘a driving~ primary pumpgear on the
driving shaft, a. primary pump driven shaft, ’_
bearings therefor, a driven pump vgear'îupon said
driven shaft and meshing A‘with the driving pump
gear, a driving transmission gear driven from
said driven shaft, a driven transmission gear
driven from the driving transmission gear,- a
4
2,108,771
shaft and bearings therefor, a driving secondary
ings in the rear plate and the body at opposite
pump gear mounted upon the driven transmis
sion shaft, a driven secondary pump gear adapted
ends of the driven transmission gear, a driving
secondary pump gear mounted upon the driven
transmission shaft, a bearing for the driven
to mesh with and be adjusted axially with respect
to’ the driving secondary pump gear, walls form
ing a cylinder fitting the driven secondary pump
gear, pistons at opposite ends of the driven sec
ondary pump gear, movable in the cylinder, one
of them having an arcuate recess to accommodate
10 the driving secondary pump gear, a ñller for the
recess, a rod for shift-ing the pistons »and driven
transmission shaft between the driving secondary
pump gear and the front plate, a secondary
driven pump gear adapted to be adjusted axially
of the driving secondary pump gear, walls form
ing a ycylinder within which the driven secondary
gear moves, pistons at opposite ends of the sec
10
ondary driven pump gear movable in the cylinder,
one of them having an arcuatel recess to ac
secondary pump gear axially, the section of the
rod and filler being approximately equal at the ' commodate the driving secondary pump gear and
two ends of the cylinder, walls forming a passage sealed longitudinally of the recess by the bear
15 equalizing fluid pressures at the two ends of the .ing member for the driven transmission gear 15
cylinder, and walls forming an inlet and an out
shaft, means for shifting the pistons and driven
let for fiuidvpumped and a fluid connection be
secondary pump gear longitudinally, walls form
tween the pumps,
,
a
v3. A gear pump comprising front and back
20 pump plates, a body between the plates, means
'ing a by-pass from one end of the cylinder to the'
other, walls forming an inlet to the primary
pump, an outlet from the secondary pump, fluid 20
series connection between the pumps, and trans
for connecting `.the plates against the body pro
tecting against leakage, a driving shaft havingl mission gearing between the pumps operating the
bearing in the front plate and body, a driving pri
secondary pump at high speed with respect to the
mary gear on the driving shaft, a primary pump
25 driven shaft having bearings in the front plate ' ä
and body, a driven pump gear upon thedriven
primary shaft and meshing with the driving pri
mary gear, a driving transmission gear also upon
the driven primary pump shaft, an idler shaft
30 having bearings in the rear plate and body, an
idler thereon meshing with the driving trans
mission gear, a driven transmission gear shaft, a
driven transmission gear thereon driven by the
idler, the driven tr’ansmission gear shaft having
bearings in the rear plate and the body at opp'o
site ends of the driven transmission "gear, a driv
ing secondary pump gear mounted upon the
driven transmission shaft, a bearing for the driven
transmission shaft between the secondary pump
40 gear and the front plate, a secondary drivenv
pump gear adapted to be adjusted axially of the
driving secondary pump gear, walls forming av
cylinder within> which `the driven secondary
is. Ul
primary pump.
.~
5. A casing, a. primary pressure pump, a sec
25
ondary gear pump having series fluid connections
with the primary pump, one gear of which sec
ondary pump is shiftable within a cylindrical
space in the casing, and of smaller secondary
pumping capacity than the capacity ofthe pri 30
mary pressure pump, whereby a portion only of
the fluid discharging from the primary pump is
pumped by the secondary gear pump and the
secondary gear pump is constantly supplied under
pressure from the primary pump, means provid 35
ing for the discharge of the over-supply of ñuid,
the structure being characterized by a shaft for
longitudinally moving the shiftable gear within
the cylindrical space, a shield adjacent the sec
ond secondary gear, pistons at opposite faces of 40
the shiftable gear fitting the walls of the cylin
drical space, one of said pistons surrounding the
shaft and the other of> which pistons is cut away
pump gear moves, pistons at opposite ends ofthe
secondary driven gear movable in'the cylinder,
one of them having an arcuaterecess to accom
to pass over the secondary pump gear which is
not shifted and to pass over the shield, to protect
modate the driving secondary* pump gear and
sealed by the bearing member for the driven
the ends of ,said space and walls forming a by- .
an outlet from the secondary _pump and 'a series
surrounded by the one piston and the cut-away
part of the other piston being approximately 55
equal, whereby the total volume of the by-pass
plus the portions of the said cylindrical space
longitudinally beyond the'pistons remains sub
stantially the same at all positions of the shift
against excessive leakage of liquid pumped into
45
pass within the body of the casing of the pump
transmission gear shaft, means for shifting the » ‘between opposite ends of the cylindrical space
50 pistons- and driven secondary pump gear longi
whereby pressure ofv trapped fluid in the cylin 50
tudinally, walls forming a passage for èqualizing drical space interfering with shifting of the gear
fluid pressures at the two ends of »the cylinder, of the pump is relieved andv shifting is facilitated,
walls forming an inlet to the primary pump and the effective cross sectional areas of the shaft
55 yconnection between the pumps, the transmission
gearing between the pumps operating the second
ary pump at higher speed than the speed of the
.primary pump.
'
»
4. A gear pump comprising front and back
60
pump plates, a\body between the plates, means -able gèar.
for connecting the plates against thebody pro
tecting against leakage, a driving shaft having
bearings in the front plateJ and body and packed
6. vA casing, a primary pressure gear pump, a
secondaryv gear pump fed therefrom through se
ries fluid connections between said pumps and of
smaller pumping capacity than the capacity of
, within the front plate, a driving primary gear
' on the driving shaft, a primary pump driven ` the primary pressure pump whereby a portion only 65
shaft „ having bearings in ` the front and rear
plates, a driven pump gear upon the driven pri
mary shaft and meshing with the driving primary
gear,v a driving transmission 'gear alsouponthe
of the fluid discharging from the primary pump
is pumped by the secondary gear pump and the
secondary gear pump is constantly supplied under
pressure from the primary pump, one of the gears
Adriven primary pump shaft, an idler shaft hav-. > of the secondary pump being axially adjustable 70
ing bearings ~in the rear plate and body, an idler and` the other of which gears4 is axially fixed,
thereon meshing with the driving transmission means providing for the dischargel of an over
gear, a' driven transmission gear shaft, a driven supply of fluid suppliedl to the secondary pump,
.transmission gear thereon drivenby the idler, . the structure being characterized by walls form
_ ing a cylinder in the casing co-axial with and 75
'75 the' driven transmission gear shaft having bear
‘
2,108,771
5
containing the adjustable gear of the secondary
pump, a shaft for axially shifting the adjustable
gear within said cylinder with respect to the ñxed
forming a cylinder therein, interconnecting gears
Which‘together form a secondary pumping ele
ment, one of which gears is fixed against axial
gear, a shield in line with the fixed gear and
movement and the other of which is axially mov
able in the cylinder, means for axially moving
said movable gear comprising a shield having a
extending into the cylinder from the side, pis
tons at opposite faces of the adjustable gear
sealing against the walls of the cylinder, one pis
ton surrounding the shaft and the other of which
pistons is cut away to pass over the fixed gear
10 and seal against it and against the shield to pro
tect against excessive leakage of the» liquid
portion extending into the cylinder from its side
at one end of the axiallyñxed gear, a piston con
nected with the axially movable gear and adapted
to seal with the cylinder and having one side re 10
cessed and sealing against the shield, a second
piston fitting the cylinder and a shaft upon which
the pistons are mounted, passing through the cas
pumped into the ends of the cylinder, and walls
forming a by-pass between opposite ends of the
cylinder whereby pressure of‘the trapped duid v ing and of cross-section approximately that of
in the cylinder interfering with shifting of the the recess in the first piston whereby the` total
volume of the portions of the cylinder space axial
gear of the pump is relieved and shifting is facili
tated, the eiî'ective cross-sectional areas' of the ly beyond the two pistonsris approximately the
shaft surrounded by the one piston and the cut- t same irrespective of the adjusted position of the
away part of the second piston to seal with the" two pistons, the construction being provided with
shield being approximately equal whereby’ the a by-pass from one end of the cylinder to the 20
total volume of the by-pass and of the‘portions other through a part ñxed during normal opera
of the said cylinder space longitudinally beyond tion whereby fluid is free to pass between the
the pistons remains substantially the same in all two ends of the cylinder and means for shifting
said shaft.
,i
positions of the adjustable gear.
JOSEPH PAUL LAIRD.
25
’1. In a gear pumping device, a casing, walls
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