Note: Descriptions are shown in the official language in which they were submitted.
11 I
Q~
B~C~GROUND OF ~E }NVEN~ION
In flow control devices of the orifice restriction type
constant flow rates are achieved when the pressure drop across
the device is sufficient to permit fluid inertial effects to
substantially restrict flow rates regardless of further increases
in upstream fluid pressure. Flow control devices of this type
find a wide variety of uses ranging from controlling flow rates
in shower heads to applications in which irrigation line flow
rateS must be controlled to conserve water usage.
A performance aspect associated with prior art devices
is that the flow rate increases at a rate directly proportional to
the pressure drop across the device until a relatively large
pressure differential is reached in which fluid inertial effects
limit flow. Some flow control devices have employed a bypass
feature partially compensating for this aspect, but experience
has shown that the bypass feature becomes inoperative at higher
pressure differentials resulting in a mar~ed discontinuity in
the flow rate. The inability of prior art bypass techniques to
overcome this shortcoming has been due primarily to the
difficulty of controlling and maintainirg bypass flow passages
around the outer diameter and periphery of the downstream face of
the control member where pressure and viscous forces are most
severe, and has resulted in excessive control member deflection.
~1~0~
The present invention overcomes the above-
described disadvantages of the prior art by substantially
reducing deviations from a constant flow rate and provides.
sufficiently effective control of the flow such that, during
low pressure differential conditions, a constant flow rate
is more closely maintained.
According to one aspect of the present invention,
there is provided a method for fluid flow in a conduit
having an inlet and an outlet at a substantially constant
rate over an intended range of varying fluid inlet pressures.
The method includes flowing the fluid through an enlarged
section in the flow area of the fluid conduit intermediate
the inlet and outlet and disposing a resilient washer trans-
versely of the flow in the section and spacing the outer
periphery thereof from the inner wall of the section to
permit bypass flow therebetween. The downstream face of
the washer is maintained spaced from the wall of the enlarged
section of the conduit such that the bypass flow is not
blocked as the washer deflects transversely under increased
forces of increased inlet pressure, thereby maintaining the
bypass flow additive to the central flow through the washer
at all inlet service pressures.
According to another aspect of the present
invention, there is provided a flow control washer operative
upon placement in a fluid conduit having an inlet and
outlet to permit primary flow therethrough and bypass flow
t~erearound and to maintain the flow between the inlet and
outlet substantially constant throughout a range of intended
inlet service pressures. The washer has a primary flow
aperture therethrough with means defining in cooperation
~ith the fluid conduit at least one axial flow passage
extending along the outer periphery of the washer from the
p -2-
~ )
upstream face to the downstream face thereof. Spacing
means is disposed on the downstream face of the washer,
the spacing means being operative, upon the washer being
subjected to an inlet pressure less than a first predeter-
mined value, to provide a predetermined maximum level of
bypass flow and the spacing means being operative upon
the washer being subjected to inlet pressures greater than
the first level by a predetermined amount, to maintain the
bypass flow at a reduced predetermined minimum level so
that the washer maintains substantially constant flow
throughout the pressure range.
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ll llOOOi3
BRIEF DESCRIPTION OF T~E DRAWINGS
FIGVRE 1 is an axial cross section of the invention in
operation under low differential pressure conditions.
FIGURE 2 is an axial view similar to Figure l taken
S through section indicating lines 2-2 showing the downstream face
of the control member.
FIGURE 3 is a cross-sectional view of the invention
similar to Figure l illustrating maximum deflection of the
control member resulting from high differential pressure
conditions.
FIGURE 4 is an elevation view in cross section of a
second embodiment of the invention.
FIGURE 5 is a graph of flow rate versus pressure
differential for a flow control device of the present invention
and also a typical flow control device lacking bypass control.
DETAILED DESCRIPTION
Referring now to Figure l, a flow control device is
indicated generally by reference numeral 10. An upstream housing
section 12 and a downstream housing section 14 are joined and
fluidly sealed together by any convenient expedient compatible
with the material used for fabrication. Where plastic has been
used for sections 12 and 14, sonic welding has been found to be
particularly satisfactory. Upstream housing section 12 has an
inlet passageway 16 formed in a tubular portion 18 thereof.
Downstream housing section 14 has an outlet fluid passageway 18
formed in a tubular portion 22 thereof. An intermediate flow
chamber 23 is defined by housing sections 12 and 14 and is bounded
by an upstream wall 24, a downstream wall 25, and a cylindrical
bore having an internal diameter 26. A disc-shaped flow control
member 27 having a centrally located metering orifice 36 is
disposed within flow chamber 23 and is formed of a resilient
material, preferably an elastomer. The control member has a
plurality of lobes or extensions projecting radially outwardly
from the outer periphery thereof in preferably circumferentially
equally spaced arrangement, a typical one of which is indicated
by reference numeral 28. Flow chamber internal diameter 26 is
appropriately sized for slidably maintaining the flow control
member 27 transversely in a desired position. The circumferential
spaces between individual lobes 28 and internal diameter 26 of
the fluid chamber define fluid passageways which function in a
manner that will be subsequently described. The flow control
member 27 has a preferably flat upstream surface 32 and a
pr~ferably concave or dished downstream surface 34. A plurality
of pads 35 are formed on upstream surface 32 and serve to space
the control member from upstream wall 24.
With continued reference to Figure l,and additionally
Figure 2, projections 38, 40 and 42 are formed around the outer
periphery of downstream surface 34 while an inner group of
projections 46, 48 and 50 are formed near metering orifice 36 and
preferably circumferentially equally spaced thereabout. The
ll~Qi3
inner group of projections are spaced radially outward from
orifice 36 an amount sufficient to clear the inner diameter of
outlet passage 20. With continued reference to Figure 1, the
outer group of projections 38, 40 and 42 project axially from
. 5 - downstream s~face 34 . a pxedetermined amount greater than the
axial projection of the inner group of projections 46, 48 and.
S0 such that the flow control member, while in a substantially
unflexed condition as illustrated in Figure 1, has only the .
: outer projections 38, 40 and 42 thereof contacting the downstream
wall of the fluid chamber.
By way of illustration, a typical configuration for a `
flow control element rated at approximately 0.80 gallons per
minute is characterized as having a metering orifice with an
internal diameter of 0.097 inch (2.46 mm), an outer diameter of.
0.500 inch (12.7 mm), a thickness of 0.125 inch (3.17 mm), an
axial concavity in the downstream face to a depth of 0.014 inch
(0.35 mm), an axial extension beyond the downstream face for the
outer group of projections of 0.008 inch (0.20 mm), and an
axial extension beyond the downstream face, measured at the point
of maximum concavity, for the inner group of projections of 0.014
inch (0.35 mm). The parameters outlined above can be used to
formulate relationships respecting flow control member configura-
tion. For example, the ratio of outer diameter to axial
thickness controls the transverse flexibility for a given
2~ material. This ratio R is held substantially constant and a
particular suitable ratio for elastomeric material has been
- 5 -
ll~Q ~;~
found to be 5:1, however, other ratios may be employed for other
materials. For a given flexibility of the control member the
response of the bypass flow component can be established by the
- spacing of the downstream face, at the inner group of projections
from the downstream wall and also the spacing from the ends of
the inner group of projections from the downstream wall. In the
presently preferred practice this spacing of the downstream face
from the downstream wall may be ex~ressed as a percentage of
the metering orifice diameter and a particular satisfactory
-10 value for elastomeric material has been found to be 20 percent,
however, it will be understood other values may be appropriate
for other materials. In a similar fashion the spacing of the
ends of the inner group of projections, in the axially relaxed
condition, from the downstream wall may be expressed as a
percentage of the metering orifice diameter and a particular
satisfactory value for elastomeric material has been found to be
8 percent; however, it will be understood other values may be
appropriate for other materials. By altering the ratio R, the
amount of axial deflection for a given pressure differential
can be adjusted to achieve, in cooperation with the inner group
of projections and depth of concavity, a bypass flow response
to suit varying application requirements.
In operation, fluid flow enters inlet fluid passageway
16 and, when under relatively low pressure differentials as,
for example, of the order of 1 - 2 psi as measured across the
inlet and outlet passages, ~ollows a path indicated by the black
arrows in Figure 1. Axial deflection of the flow control member
at low pressure differentials is minimal and the control mem~er
assumes a shape substantially as shown in Figure 1. Even at such
low pressure differentials the fluid forces are, however, suffi-
cient to thrust the flow control member against downstream wall
25. A portion of the total fluid flow carried by inlet passage
16, designated as primary flow, flows directly through metering
orifice 36 and into outlet passageway 20. That portion of the
flow not passing through metering orifice 36, designated as
bypass flow, follows a path radially outward between the upstream
surface 32 of the flow control member and the upstream wall 24 of
flow chamber 23. Upon reaching the wall of the flow chamber at
internal diameter 26, the fluid then flows through the spaces
between lobed extensions 35 and in a direction parallel to flow
through metering orifice 36. Upon reaching the downstream wall
25 of the flow chamber the fluid enters the space between the
downstream surface 34 and the downstream wall 25 of the flow
chamber. The concavity of downstream surface 34 of the control
member serves to offset the reduction in cross-sectional flow
area as the fluid approaches the center of the control member.
The bypass flow component combines with the primary flow
component exiting from the metering orifice whereupon flow
continues on through outlet fluid passage 20. The function of
the bypass flow feature is to permit a greater volume of bypass
fluid to flow through the device than would be possible solely
through the metering orifice under conditions of low differential
pressures.
. Il
11~ 3
As the upstream line pressure increases, the flow rate
through the bypass path described above increases accordingly,
during which time the flow control member is axially deflected
by the pressure differential existing across the flow member and
also the forces due to fluid viscosity. The axial deflection,
which is maximum near the center of the flow control member,
continues to increase until the inner group of projections 46,
48 and 50 abut downstream wall 25. The axial projection of the
inner group of projections, plus the amount of concavity, is
chosen to achieve a predetermined bypass flow characteristic
which, when added to the primary flow through the metering
orifice 36, results in substantially constant flow rate across a
wide range of pressure differentials. It should be noted that, a
the flow rate increases, the contribution to total flow required
from the bypass component becomes diminished. However, it has
been found desirable to maintain a predetermined amount of bypass
flow throughout the full range of service pressure differentials
in order to prevent collapse of the flow control member against
downstream wall 25 and a discontinuity in the resultant flow
rate. By placing the inner projections 46, 48 and 50 near the
point of maximum axial deflection of the flow control member,
significantly improved control over the bypass flow component can
be achieved by limiting axial deflection of the flow control
member to a predetermined amount. A graphical representation of
the bypass flow component for a flow control member having this
control feature blotted as a function of pressure drop would be
characterized by a substantially linear increase to a given
maximum followed by a controlled drop-off to a given minimum.
Thus, an abrupt closing-off of the bypass component which would
result in a sudden drop in the resultant flow rate is avoided.
11~ 3
The above-described performance aspects are illustrated
in Figure 5 by a graph of flow rate versus pressure differential
as measured across the inlet passage to the outlet passage.
Curve "A" represents the resultant flow rate of the invention
incorporating the controlled bypass feature disclosed above
while curve "B" represents resultant flow for a control device
without controlled bypass flow. In the region from 0 psi to
approximately 3 psi both devices permit flow to increase at a
substantially linear rate until maximum values are reached.
During this stage of operation, axial deflection of each device
has been minimal. Beyond the point of maximum flow rate, however
axial deflection for both devices increases rapidly causing a
reduction in cross-sectional flow area along the bypass flow
path as indicated in the region from 3 psi to 5 psi. The abrupt
reduction in flGw rate evidenced by curve "B", over 25 percent,
results from closing-off of the bypass passage. In contrast,
curve "A" drops off less than 6 percent, a significant difference
in performance from curve "B." Beyond 5 psi differential
pressure the resultant flow rate of curve "A" is substantially
constant. The remainder of curve "B" beyond 5 psi differential
exhibits a gradual increase in flow occurring through a central
orifice.
Figure 3 illustrates the flow control member under
relatively high differential pressure conditions at which
maximum axial deflection has occurred and where furthQr axial
deflection is prevented by the abutment of the inner group of
projections 46, 48 and 50 against the downstream wall of the
fluid chamber.
. Il
ll~g;iQ~3
Referring now to Figure 4, there is illustrated a
second embodiment of the invention in which the outer and inner
group of projections are integrally formed on the downstream wall
of downstream housing section 14, the embodiment of Figure 4
being otherwise similar to the embodiment of Figure 1. Reference
numerals 54 and 56 designate typically two of a plurality of
axially extending circumferentially spaced outer projections
while reference numerals 58 and 60 designate a typical pair of
similarly arranged inner projections located near the central
metering orifice. In the preferred practice of the invention
at least three outer and inner`projections are employed in order
to maintain satisfactory alignment and spacing of the flow
control member with respect to downstream wall 25. A greater
number, however, may be utilized where required by fluid flow
rates and viscosities.
The operation of the second embodiment of the invention
is similar to the operational characteristics hereinabove
described for the first embodiment.
The embodiments of the invention as shown and described
above are representative of the inventive principles as stated
herein. It is to be understood that variations and departures
can be made from the embodiments as shown without, however,
departing from the scope of the appended claims.
