Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to fluid flow apparatus and is
particularly directed to improvements in check valve construction
and backflow prevention apparatus.
Check valves are commonly provided when it is desired
to permit fluid flow in one direction but to prevent fluid flow
in the other direction. A single check valve acting alone may
leak slightly and, therefore, single check valves are not used
when it is necessary to prevent any reverse flow, even in the
smallest degree. In the latter situation, backflow prevention
apparatus may take the form of two check valves connected in
series with a "zone" between them. Both check valves remain
open during normal flow in a forward direction, but in the event
that the downstream pressure should approach the upstream
pressure within a predetermined amount, for example, two pounds
per square inch, the volume of the zone between the check valves
is vented to atmosphere. In such devices, downstream pressure
can never exceed upstream pressure, even under vacuum condi-
tions with the result that reverse flow is not possible.
Backflow prevention devices of the type just described
have at least two serious shortcomings. The first is that, in
order to have a check valve which will close satisfactorily
and more significantly, in certain cases, maintain a predetermined
minimum pressure, a spring force is used, and this must
be overcome during normal flow in the forward direction. Unfor-
tunately, this often results in a pressure drop of serious pro-
portions, particularly when two check valves in series are
employed. Another difficulty is that conventional apparatus for
venting the zone between the check valves is usually costly,
inaccurate and difficult to maintain.
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Accordingly, it is the principal objective of this invention to pro-
vide check valves suitable for use in backflow prevention equipment and that
are constructed to both provide a relatively high initial resistance to pres-
sure and flow and yet as the demand for flow increases, cause the correspond-
ing pressure drop to be at a minimum value.
According to one aspect of the invention there is provided in a
check valve, the combination of means forming an inlet passage terminating in
a stationary inclined annular valve seat, an inclined stationary barrel posi-
tioned coaxially of the valve seat, the barrel having a cylindrical wall, a
valve poppet movable toward and away from said valve seat, a spring acting to
move said valve poppet into sealing contact with said valve seat, said spring
acting to create a pressure drop when said valve poppet is initially moved
away from said seat by fluid pressure in the inlet passage, said valve poppet
having axially spaced flanges slidably guided within said wall of said barrel,
means cooperating with said barrel and said valve poppet to define a chamber
remote from said valve seat, means forming a discharge passage, a portion of
said wall and one of said flanges projecting into said discharge passage to
create a zone of relatively rapid flow and consequent reduced pressure, and
means establishing communication between said zone and said chamber, whereby
forward flow of fluid through the check valve causes a reduction in pressure
in the chamber to oppose the action of said spring.
Embodiments of the invention will now be described, by way of example,
with reference to the accompanying drawings, in whi~h:
Figure 1 is a sectional elevation showing a preferred embodiment of
the check valve of this invention, the inlet and outlet terminals being coaxial
and the axis of motion of the check valve poppet being positioned at a 45
angle.
Figure 2 is a sectional view of a similar check valve, the inlet and
outlet terminals being positioned at 90 and the axis of movement of the check
valve poppet being coaxial with the inlet axis.
Figure 3 is a sectional view of a similar check valve, the inlet and
outlet terminals being coaxial and the axis of movement of the check valve
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poppet being at right angles thereto.
Figure 4 is a sectional view of a similar check valve, the inlet and
outlet terminals and axis of movement of the check valve poppet all being co-
axial.
Figure 5 is a sectional elevation showing a preferred form of double
check valve assembly, both check valves being shown in closed position.
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Figure 6 is a graph showing pressure loss plotted against flow rate
in a commercial form of the double check valve assembly shown in Figure 5.
One curve of the graph relates to a device of three-quarter inch nominal
size and the other curve relates to a device of one inch nominal size.
Figure 7 is a side elevation showing a complete back-flow preventer
assembly embodying this invention.
Figure 8 is an end elevation of the device shown in Figure 7.
Figure 9 is a schematic diagram in sectional elevation showing a
double check valve assembly and its connections to a differential control
valve assembly, the parts being shown in position for full flow in the normal
direction.
Figure 10, on the same sheet as Figures 7 and 8, is a graph showing
pressure loss plotted against flow rate for the backflow preventer device
shown in Figures 7-9. One curve of the graph relates to a device of three-
quarter inch nominal size and the other curve relates to the one inch nominal
size.
Figure 11 is a sectional view showing a modified form of differential
pressure control valve, the parts being positioned for normal forward flow.
Figure 12 is a view similar to Figure 10, the parts being in
position corresponding to backflow conditions.
Referring to the drawings, the check valve assembly generally
designated 10 is shown in its various embodiments in Figures 1, 2, 3 and 4.
The check valve assembly 10 includes a poppet 11 slidably mounted within a
stationary barrel 12. An annular resilient ring 13 serves as a valve face and
is held in place on the poppe 11 by means of a retaining washer 14 and a
threaded fastening 15.
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A coil compression spring 17 acts on the poppet 11 to bring
the resilient ring 13 into sealing engagement with the station-
ary annular seat 18 provided at the end of the inlet passage 19.
The poppet 11 has a first flange 20 and a second
flange 21 both slidably mounted within the stationary barrel 12.
An annular groove 22 is defined between the flanges 20 and 21
and one or more ports 23 establish communication between the
groove 22 and the spring chamber 24. In Figure 1, the inlet
terminal 26 and the outlet terminal 27 are coaxial, and the
axis of movement of the poppet 11 is positioned at about 45
with respect thereto. In Figure 2, the inlet teTminal 26a and
the outlet teTminal 27a are at right angles, and the axis of
movement of the poppet 11 is coaxial with the inlet terminal
26a. In Figure 3, the inlet terminal 26b and the outlet terminal
27b are coaxial, and the axis of movement of the poppet 11 is
at right angles thereto. In Figure 4, the inlet terminal 27c
and the outlet terminal 27c are coaxial, and the movement of
the poppet 11 is along the same axis.
The check valve assembly 10 is in open position as
shown in Figures 1, 2, 3 and 4. Fluid in the inlet 19 passes
between the annular seat 18 and the resilient ring 13 into the
outlet passage 28. Inlet pressure is then present in chamber -
29 acting upon the total pressure area of flange 20 to overcome
the force of spring 17. Thus, flange 20 effectively SeTVeS as
a seal between the pressure area 29 and pressure area 22. In
Figure 4, stationary housing 30 encircles the barTel 12 and axial
passageways 31 are provided to carry fluid from the chamber 29
to the outlet terminal 27c.
In each case the outer diameters of the poppet flanges
20 and 21 are substantially larger than the effective diameter
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of the stationary seat 18, so that when the check valve is in
closed position with the resilient ring 13 engaging the seat 18,
the pressure in the inlet passage 19 acts over a substantially
smaller area than the pressure in the spring chamber 24. When
the pressure in the inlet passage 19 applied across area of seat
18 is sufficient to overcome the force of the spring 17 and the
pressure in the spring chamber 24, both the static and the dynamic
head are subsequently applied to the larger effective area of the
flange 20. Thus, the increase in effective area when the valve
first opens results in a substantial force to overcome the spring
force, and the valve moves advantageously toward the open position.
When the check valve parts are in open position corre-
sponding to forward flow operation, as shown in Figures 1-4, the
flow of the fluid creates a low pressure region around the poppet
ll in the groove 22. This occurs because a portion of the flange
20 and a portion of the groove 22 extend into the outlet passage
28. This reduced pressure is transmitted to the spring chamber 24
through the groove 22 and through the port or ports 23, as well as
through the clearance between the flange 21 and the barrel 12.
Consequently, as the velocity of forward flow increases, the unit
pressure in the chamber 17 decreases over the effective area
defined by the diameter of flange 20.
When the pressure in the outlet passage 28 falls below
a predetermined value, as compared to the pressure in the inlet
passage l9, the portion of the poppet 11 which protrudes into the
outlet passage 28, Figures 1-3, and the entire poppet in Figure 4,
receives the full static and dynamic force of the fluid in reverse
flow, the force as thus developed acts over the full effective
area of the spring chamber 24, which combined with the force of
the spring 17 acts to close the valve promptly.
It will be observed that, in the construction just de-
scribed, as the velocity of forward flow increases, the velocity
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head produces a positive opening force on the poppet 11 on the
side containing the resilient ring 13 together with a lowering
of unit pressure in the chamber 24, both effects serving to
overcome the force of the spring 17. Moreover the lowering of
pressure in the spring chamber is developed due to the portion
of the poppet flange 20 protruding into the outlet passage 28
and creating a restriction 77 in which the momentum of fluid
flow acting upon the static fluid in groove 22 results in the
lowering of pressure in groove 22 and transmitted to the spring
chamber through the communicating port 23. Consequently, as
the demand for flow increases, the resulting momentum increase
results in an ever decreasing pressure in the spring chamber.
Concurrently, as the rate of flow increases, the velocity head
acting upon the full effective area of flange 20 (on the side
with the resilient seal) increases. With both effects thus
combined, a substantial pressure differential is created across
the flange 20 to create an increasing force to overcome the
force of the spring. Furthermore, even with the introduction
of restriction 77 and a consequent "induced" pressure drop at
that point, the net result is an advantageous pressure differ-
ential across the poppet and a reduction in the total pressure
drop across the valve. Moreover, the spaced flanges 20 and 21
guide the poppet in its movements within the baTrel 12 with
adequate clearances to avoid mechanical frictional losses to
minimize mechanical malfunctions. The absence of guide pins,
toggle levers, etc., also assists in the reduction of mechanical
friction.
The double check valve assembly generally designated
33, shown in FiguTe 5, employs two duplicate check valve assem-
blies lOa and lOb which are substantially the same as the checkvalve 10 described in detail above. These check valve assemblies
are arranged at right angles, the check valve lOa assembly being
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positioned at 45 to the axis of the inlet terminal 34 and the
check valve assembly lOb being at 45 to the axis of the outlet
terminal 35. The construction and operation of each of these
check valve assemblies lOa and 10_ is the same as that of the
check valve assembly 10 described above. Moreover, the geometric
relationship of the assemblies lOa and 10_ as shown in Figure 5
produces a uniform flow pattern by minimizing the extent o-E the
changes in direction of flow and the extent of obstructions to
forward flow, thus minimizing fluid pressure losses.
The chart of Figure 6 shows the pressure loss through
the double check ~alve assembly of Figure 5, for both the nominal
size of three-quarter inch and the nominal size of one inch. It
will be observed that the pressure loss through the assemblies
lOa and 10 actually falls off as the flow rate increases, up to
about 15 gallons per minute for the three-quarter inch size and
up to about 18 gallons per minute for the one inch size.
It will be observed that the moving parts of each check
valve assembly lOa and 10_ may be installed and removed independ-
ently without any need to disconnect the entire assembly from
the line. Moreover, each check valve assembly is so arranged
as to utilize the full impact of the dynamic pressure in the
support line when in forward flow operation, for effectively mini-
mizing hydraulic pressure losses. Furthermore, each check valve
assembly is so arranged as to have portions of the poppet thereof
protruding into its respective discharge passage, or in communi-
cation with its discharge passage, so as to be responsive to the
slightest reverse flow action, closing spontaneously to prevent
backflow.
The backflow preventer assembly shown in Figures 7, 8,
and 9 include a double check valve assembly 33 having its inlet
terminal 34 connected to a supply pipe 36 through a shutoff valve
37 and a union coupling 38. The outlet terminal 35 of the double
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check valve assembly 33 is connected through union coupling
39 and shutoff valve 40 to the service pipe 41.
A control valve assembly 43 is connected to the
double check valve assembly 33 by means of discharge pipe 44
and pressure-sensing lines 45 and 46. The discharge pipe 44
forms a portion of the stationary housing 47 which contains a
removable valve seat 48. A valve stem 49 carries a valve head
50 at its lower end and a resilient disk 51 on the valve head
closes against the seat 48. When the parts are in position as
shown in Figure 9, the valve is closed and therefore discharge
of fluid from the port 52 in the double check valve assembly 33
through discharge pipe 44 is prevented. The port 52 is located
downstream from the check valve lOa.and upstream from the check
valve lOb.
Means are provided for moving the stem 49 to open or
close the valve 48, 50, and as shown in the drawings this means
includes flexible diaphragm 54 having its outer periphery clamped
between the flange 55 on the housing 47 and the flange 56 on the
cover 57. The inner portion of the diaphragm 54 is clamped to
the stem 49 between the plates 58 and 59. A seal ring 60 on the
stem 49 slides within the housing bore 61, and a seal ring 62 on
the annular piston 63 of the stem 49 slides within the housing
bore 64.
A chamber 65 is formed within the housing 47 below the
diaphragm 54 and a chamber 66 is formed above the diaphragm within
the cover 57. The chamber 65 communicates through passage 46 and
port 67 with the inlet passage 68 of the check valve assembly lOa.
The chamber 66 is connected through cover port 69, passage 45 and
port 70 with the inlet passage 71 for the check valve assembly
lOb. From this description it will be understood that the differ-
ential pressure across the diaphragm 54 is the same as the differ-
ential pressure between the inlet passage 68 and the inlet passage 71.
1~6~64
The coil compression spring 73 in the chamber 66 acts
on the diaphragm plate 58 to move the stem 49 in a direction to
open the discharge valve 48, 50. The force of the spring is
assisted by the unit pressure in the chamber 66 and is opposed
by the unit pressure in the chamber 65. This opposition force
is increased by the fluid pressure acting against the underside
of the annular piston 64. The annular space above the piston
64 and within the housing 47 is vented to atmosphere through
vent port 74.
In operation, the differential control valve 43 serves
to vent the zone between the check valve assemblies lOa and lOb
through the discharge port 52 whenever the downstream pressure
approaches the upstream pressure within a predetermined amount.
Thus for example, the parts may be designed and adjusted so that
when the pressure in the inlet terminal 34 is less than two PSI
greater than the pressure in the outlet terminal 35, the differ-
ential control valve 43 will open to permit fluid to flow from
the zone port 52 through the pipe 44 and through the open valve
48, 50 to atmosphere. The several forces applied to the stem
49 in addition to gravity are the opposing forces developed by
inlet pressure reflected in chamber 65, outlet pressure reflec-
ted in chamber 66, zone pressure at port 52 reflected against
piston 63, as well as on discharge valve 50, and the force of
spring 73.
It will be observed that the effective area of the
diaphragm 54 is much greater than that of the valve seat 48.
Also, the ports 67 and 70 are angularly positioned to
reflect both static and dynamic pressures in their respective
passages. Accordingly, the differential control valve 43 causes
fluid to be vented out through zone port 52 whenever the outlet
passage pressure from check valve assembly lOa (reflected through
line 45) plus the force of the spring 76, plus the effect of
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~.~r~vity, exceeds the inlet pressure from passage 68 (reflected
through line 46) acting in chamber 65. The balance piston 63 has
the same effective area as that of the seat 48, plus that of the
communicating stem 49, so that the pressure exertedon the valve
head 50 and the sliding stem 49 is balanced out by the pressure
exerted on the piston 63. In similar fashion, the differential
control valve 43 remains closed to prevent loss of fluid through
the zone port 52 so long as the total force generated by inlet
pressure in the chamber 65 exceeds the sum of the force generated
by outlet pressure in chamber 66 supplemented by the force of the
spring 73 and by the effect of gravity.
The chart of Figure 10 shows the pressure loss through
the backflow preventer assembly shown in Figures 7 and 8, for
both the nominal size of three-quarter inch and the nominal size
of one inch, when normal flow occurs in the forward direction.
It will be observed that the pressure loss through the entire
backflow preventer assembly actually falls off as the flow rate
increases up to about 20 gallons per minute for the three-quarter
inch size, and up to about 32 gallons per minute for the one inch
size.
In the modified form of differential control valve shown
in Figures 11 and 12, an axial passage 75 in the stem 49a replaces
the cover port 69. This passage 75 and its side outlet port 76
establishes communication between the cover chamber 66 and the dis-
charge pipe 44. Only one sensing line 46 is used, and it connects
the chamber 65 through line 46 to the inlet passage 68, as de-
scribed above. The sensing line 45 and port 70 are not used.
Figure 11 shows the parts of the diaphragm control valve in closed
position corresponding to normal forward flow operation, and
Figure 12 shows the same parts in position to discharge fluid from
the zone port 52 to atmosphere when backflow conditions are present
or imminent. In other respects, the construction and operation of
the modified form of the diaphragm control valve shown in Figures
11 and 12 are the same as that previously described.
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Havin~ fully described our in~ention, it is to be
understood that we are not to be limited by the details herein
set forth but that our in~ention is of the full scope of the
appended claims.
