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Патент USA US2407190

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Sept. 3,' 1946.
w. o. TAIT
Filed „nine 50, 1944
/fv aff/WOR
M4 0. 7A? / T
. j 5y
Patented Sept. _3, '1946
i >`Williamp.Tait,"Garden City, N. Y., assignor to
Sperry Gyròscopé Company, Inc., a corpora
"tion of New York `
’ [1f
Y „Applicationìniiièsd1944,seria1N0.54as55
’i (Banner> (Cl. 21a-'7164)
'Iì‘his invention relates to the artV of filtering
and is particularly concerned with a novel method
of and apparatus for filtering fluids in reverse flow
circulating systems, While theY invention hasa
special _utility inrconnection with high pressure
hydraulic servo systems _it _has awide range of
application in filtering fluids lin. fluid circulating
channel. -In other words, the pressure difference
above mentioned is in the -nature of a drop in
static pressure between any section in the uncon
stricted region of the l fluid channel and the
5 throat of the _channel Whether that section be
upstream or downstream of the throat. Hence,
by operatively connecting a filter ,between any
systemsof all types.
A, u
. Y
point subject `to relatively high pressure and a
For several reasons filtration of the working
point of reduced pressure in the fiow channel, a
fluid in reversible ñow high pressure systems has 10 filtering system is produced in which the pressure
not heretofore appeared feasible.- With the fil
drop always occurs in the same direction irre
tration methods previously tried, reversal of fluid
flow in thesystem _has meant a reversal of pres
spective of the direction of fluid flow in the other
parts of the system, whereby a portion of the
sure within the filtering unit accompanied by the
circulating fluid .passes undirectionally through
return of foreign particles, and other previously 15 the filter even when a reversing fluid flow exists
removed substances to the main circulation chanin the main flow channels _of the system.
nels of the system, a result highly undesirable.
A similar» result is produced in unifiow systems
stricted and constrictedregions of the fluid stream
when excessive loading causes a temporary Vre
is independent of the >actual working pressure
Since the pressure drop between the uncon~
versalof flow, of the working fluid. Furthermore 20 ofthe system it is possible to control this pres
in high pressure systems a filtering element strong
sure drop by judicious selection of the cross sec
enough to resist system pressure frequently allows
tional area of the constricted region relative to
small but destructive foreign lparticles to 'pass
the cross sectionalgarea of the unconstricted'sec
through the filterV and lcontinueV in circulation.
tion and thus keep the pressure drop across the
There has also been the further diiiicult problem 25 filter small enough to prevent rupturing of the
of__ obtaining a filtering rate high enough to effece
delicate filtering elements often used to remove
tively cleanse the fluid Without unduly obstruct
small particles from the fluid in the system', even
ing the flow of fluid through thevsysterm.4 In hy
in installations where the working pressure is
relatively high. t v
draulic _systems used for control purposes, par
ticularly if high pressures are used, any com 30
Moreover since the filtering element is located
pressibility of the working medium introduces
out of _the main channel of flow and may be con
error into the operation of the controls. Obvi
nected therewith-by short, low resistance con
ously adding a filter to the system usually entails
duits, filtering of the system working-medium is
increasing thefiuid content of the system, thus
'obtained With only a slight obstruction ofthe
increasing the compressibility error above men
main` channel of flow. '
The novel apparatus and methods of the present
invention overcome the- ‘above ‘cited difficulties
in the following ingenious manner. By introduc
ing a constriction into the path of the main fluid
stream, an'increase in velocity and a reduction
in the static pressure of the stream is created in
the region of the constriction, the velocity of flow
and the static pressure of the stream in regions
removed from the constricted region being rela 45
The compactness ‘of the filtering system of th
invention makes possible the filtering of the fluidA
without materially increasing the vvolumetric
capacity of the system, hence the effecten the
compressibility error of the system is kept at a
The objects of this invention may therefore be
briefly enumerated -as‘followsz the provision of
a filter and associated circulatory system suitable
tively little affected by, this change inthe shape'
for use in a reversible flow fluid system; the pro
vision of a filter which may be used withhigh
of the channel through which the fluid passes;V
There is thus created a pressure difference be
pressure fluid systems without danger of rupture
of relatively delicate filtering materials or fine
tween points located in the reduced diameter
mesh screens; the provision of a filter having an
`region and `points located in the full diameter 50 associated circulatory or auxiliary filtering circuit
regions of the flow channel which is a function
arranged for minimum obstruction of the work
of the rate of stream flow and which operates-to
ing passages of the fluid flow system in which it
maintain the reduced diameter region at reduced
is-used; the provision of filtering apparatus hav
static pressure -irrespective of the *Y direction of
ing the smallest fluid content consistent with
fluid flow inthe constricted region ofthe »flow
effective filtering ofthe fluid in the system with
in by boss 22 on cap I1 and boss 23 on channel
which the i’ilter is employed; the provision of a
member 5, filtering element 2l being designed
filtering method suitable for use in relatively
to provide a large filtering surface in a unit of
high pressure iluid flow systems; the provision
compact dimensions.
of a ñltering system which will induce constant
Channel member 5 contains at least two, and if
recirculation of the fluid through the ñlter, thus Cil
desired may contain more than two, lateral open
producing high filtering rate and effective cleans
ings or conduits into ñltering chamber I9, these
ing of the ñuid circulating through it; and the
openings being as short as possible and being
provision of filtering apparatus having no mov
shaped to provide free and unobstructed passage
ing parts to wear rapidly or break loose and interfor the iluid between the main flow channel 6 and
fere with the operation of the system in which
the ñltering chamber I9. One of these lateral
the ñlter is installed.
openings 24 which connects filtering chamber I9
Other objects and uses of the invention- willr be
apparent from the following description and the
to throat I4 serves as an exit conduit or outlet
accompanying drawing wherein,
from the filtering chamber .to the main channel of
flow 6. One or more of these lateral openings 26
connects ñlteri'ngchamber I9 to a point of low ve
Fig. 1 is a longitudinal section through one
form of filter incorporating the principles of this
Fig. 2 is a sectional view on the line 2-2 of
Fig. 1 taken at right angles to the main path of
iiuid ñow through the ydevice of the invention,
the filtering element being shown partly in ele
vation and partly in section.
Fig. 3' is a long‘fi'tudinalV section of'- a slightly
modiñed version of the filter of'Fi'g. 1, the filter
ing element being shown partly in section and
partly in elevation.
The apparatus of' the invention, in general,
, lo‘city and high static pressure such as sections I2
or any relatively high pressure point located else
where in `the main channels of flow; such connec
tion or connections serve as inlets to lead fluid
from channel 6, to filtering chamber I9, where
the iiuid ls cleansed by passing through ñltering
element 2|, thereafter flowing' back to channel 6
by way of lateral opening 24. This invention
provides apparatus- characterizedV by> marked sim
plicity and highlyv eiïective filtering performance
which is obtained with a negligible increase in the
resistance .to the ñow of thev working substance
comprises a unit adapted to be' inserted at a con~
through the passageways of thel system.
vement point in the main' path offl'ow of a closed
In operation, iiui'd under high staticA pressure
circulatory system whose working substance or 30
fluid may require- filtering, this unit containing
a passageway which permits the iiuid to pass
through with minimum obstruction ofthe fluid
stream. In addition, means are provided for di
verting a portion ofthe fluid from the main channel of flow into an auxiliary or local path of flow
wherein the ilui'd is forced through a suitable ñl
tering element and after cleansing is> returned to
the main channel of’ flow at a point where the
cross' section of this channel has been reduced
for the purpose of creating a low pressure point
in the main fluid stream. Thus, after filtering,
the fluid in the auxiliary or filtering channel is
returned to and intermingled withv the- fluid mov
ing through the main passageways of the control
or operating system.
As illustrated in Fig; 1, one form of appara
tus in which the principles of the invention may
be embodied comprises a main channel> or' body
member 5 having a channel 6 for passing' ñuid
enters channel 6 or'member 5~ from' supply pipe
1, and ñows, for example as shown by arrow F
in Fig. l, from the' unconstricted section I2 at
the right hand end of channel 6, through the
' tapered approach passageway I5 into throat I4,
out of throat I4 through they tapered exit pas
sageway I5 into the unconstricted section I2', at
the left hand end of channel 6, from which re
gion it then flows into~` return pipe 8. As the
40 fluid passes from the upstream, unconstricted
section I2 into the throat' I4, it experiences an
increase in its velocity of flow' and a decrease in
its static pressure; as it continuesV ori its way
flowing back into the downstream, unconstricted
45 section I2, the reverse phenomenon occurs, the
velocity of stream flow decreases and the static
pressure of the fluid increases until it is' again
atf the original value, except for slight- frictiona'l
losses.- It will be noted that the pressure differ
50 ential thus created between the unconstricted
regionsl of the channel of'flow and the constricted
completely through body member 5y from supply
region I4 is alwaysv in the nature of a fall in
pipe 1 to return pipe 8 of the system with which
static pressure; and this is true whetherv the un
the' apparatus of the invention is employed, which
constricted region I2 be upstream or downstream
pipes are secured for ñuidti’ght" connection to
member 5 as by bolts 9 and flange- Iß’using pack" 55 of throat I4'. The. laterall openings 26, being
connected to regions of relatively high pressure
ing‘ glands or sealing rings || to prevent the es
I2, will always be inlet` passageways to filtering
cape of iiuid from the interior of the' system.
chamber I9, and lateral opening 24v being con
Channel 6 is formed with .a full diameter section
nected to the region of- relatively low static pres
I2 'at' each end thereof and with a throated or
constricted section I4 intermediate theA full> di 60 sure, i. e'., throat I4, will alwaysA be the outlet
passageway for flltering'chamber I9, irrespective
ameter sections I2, typically with symmetrically
of whether the fluid is flowingY from right to left
tapered funnel-shaped passageways I5, on’ both
or vice versa in channel 6. A unidirectional now
sides thereof for connecting throat I4 to- the full
of ñuid through inlets' 26, iiltering' element 2|.,
diameter or unconstricted sections I2, in the
and outlet 24 is thus providedA that is- not affected
manner of a Venturi tube.
by' a reversal of ilow through channel 6; Hence
Channel member 5 also includes a hollow lat
any foreign particles removed- from thef fluid
erally projecting, externally threaded collar I6stream by' ñlter 2| will not be'A discharged back
upon which an internally threaded cap or cover
into the working iiuid ofthe system by a reversal'
plate I1 is adapted to be> screwed’so ,as to form,
ofV the direction of flow in the system. More~
with the aid of sealing ring I8, a fluid tightv con
over, since the magnitudel of` the pressure differ
nection. 'I‘he chamber formed by collar I6 and>
ential created between throat |-4 andthe full' di'
cap ÁI‘I is appropriately shaped and properly sized
ameter regions Í'2 at the mouths of the' Venturi
to form a filtering chamber I9. Filtering cham
section in' channel 6, is a function of the velocity
ber I9 may' contain a replaceable cartridge type
of flow at these points, i‘,he~ap`paratusî of the in_
filtering element 2| held centrally secured there
vention provides a convenient means for creat
ing a safe pressure diiîerential across a selected
an internally threaded cap adapted for iiuidtîght
attachment to said collar, a ñltering chamber
filtering element irrespective of whether the sys
tem operating pressure is above or below the rup
turing pressure of the particular filtering ele
ment. Filtering of minute particles from the
formed by said collar and said cap, a re
i placeable
working fluids in relatively high pressure systems
thus becomes practicable through the use of this
element rigidly positioned
between centrally located bosses in said filtering
chamber, a small bore centrally located lateral
fluid passageway between the throat of said Ven
turi section aid said filtering chamber, and a pair
of small bore lateral fluid passageways between
said filtering chamber and points on said main
flow channel adjacent the tapered portions and
equispaced from the throat of said Venturi sec
It will be readily discerned that locating the
ñltering chamber and filtering elementl below
the Venturi section of the main flow channel re
sults in two additional advantages. Firstly, any
foreign particles which do not adhere to the fil
tering element will fall to the -bottom of the ñl
tering chamber rather than pass back into the
main fluid stream as they would do if the ñlter
tion, thus providing a simple, rugged filter par- .
ticularly suitable for use in relatively high pres
sure iluid flow systems.
2. A filtering device for filtering fluid compris
ing a conduit section adapted to form a Dart of
were above rather than below the main flow chan
a closed fluid-circulating system and shaped to
nel. Secondly, since air is lighter than the work
provide a venturi responsive to flow in either di
ing medium ordinarily. used in such systems, any 20 rection to produce a reduced static pressure and
bubbles of air which may accumulate on the ex
yincreased velocity of the fluid at one point in
terior of the filtering element are free to rise back
said conduit, an auxiliary passage leading from
into the main flow channel during periods when
another point in the same conduit as the first
point but in a region of higher static pressure
the fluid in this channel is motionless, thus pro
viding a self-Venting filter. i
and discharging into the conduit at said one
Tests of the above described ñltering device
point, and a ñltering element in said passage
have shown that a pressure difference as low as
whereby a portion of the fluid flowing in the sys
20 lb. per square inch may be obtained across the
tem is directed through the filtering element al
filter in a system where the load pressure reaches
ways in the same direction while flow in the sys
ticles with dimensions as small as 10 microns may
tem takes place in either direction.
3. A filtering device for filtering fluid com
be ñltered out of the working duid by the appa
prising a conduit section adapted to form a part
ratus of invention.
of a closed fluid-circulating system and shaped to
as high as 2000 lbs. per square inch, and that par- -
The version of the invention illustrated in Fig.
3 is `but slightly different from the device of Fig.
1. In the Fig. 3 version the taper of the approach
and recession passageways of the Venturi section
provide a reduced-diameter throat and two op
positely directed and symmetrical tapered sec
tions forming a venturi responsive to ilow in either
direction to produce a reduced static pressure and
is more gradual and a cover plate 21 secured to
increased velocity of the fluid at said throat, an
channel member 5 by holding bolts 28, 29 is used ' auxiliary passage leading from a point in said
in place of screw threaded cap l1 of Fig. l. Oth 40 conduit adjacent the outer end of one tapered sec
erwise a slight difference in physical dimensions
is the feature primarily distinguishing the Fig. 3
filter from the Fig. 1 filter. In use, these two
versions of the invention exemplify the same op
erating principle.
`Since the above described inventive concept
could be readily embodied in many apparently
different physical forms without departing from
the scope of this invention, it is intended that all
matter contained in the speciñcation or shown .
in the accompanying drawing be interpreted in
an illustrative and not in a limiting sense.
Having thus illustrated the manner in which
the principles of this invention may be applied,
what is claimed is:
1. A filter for closed fluid flow systems com
prising a body member arranged for fluidtight at
tachment to spaced conduit terminals of said
system, a main flow channel passing through said
body member, a symmetrically tapered Venturi
section having equal angles of approach and re
cession centrally located in said flow channel, a
hollow externally threaded collar integral with
and projecting laterally from said body member,
l'x 2.1
tion and discharging into the conduit at said
throat, and a filtering element in said passage
whereby a portion ofthe fluid flowing in the sys
tem is directed through the filtering element al
ways in the same direction while ilow in the sys
tem takes place in either direction.
4. A filtering device for filtering fluid compris
ing a conduit section adapted to form a part of
a closed fluid-circulating system and shaped to
provide a Venturi responsive to flow in either di
rection to produce a reduced static pressure and
increased velocity of the fluid at one point in
said conduit, means forming a ñlter chamber at
one side of the conduit section, an outlet from
the chamber comprising a short direct passage
to said one point, an inlet to the chamber com
prising a passage leading from another point of
higher static pressure in the conduit section, and
a ñltering element removably positioned in the
chamber whereby a portion of the fluid flowing
in the system is directed through the ñlterirng ele
ment always in the same direction while flow in
the system takes place in either direction.
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