Note: Descriptions are shown in the official language in which they were submitted.
1090~;7S
This application is divided out of copending Canadian application
No. 410,173, filed October 26, 1973.
This invention relates to fluid flow apparatus and is particularly
directed to improvements in 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 at sphere. In such devices, downstream pressure can never
exceed upstream pressure, even under vacuum conditions with the result that
reverse flow is not possible.
A difficulty with conventional apparatus for venting the zone
between the check valves is that it is usually costly, inaccurate, and
difficult to maintain.
Accordingly, it is the principal object of this invention to combine
a pair of series-connected check valves with a novel form of differential
control valve for venting the zone between the check valves to atmosphere
whenever the downstream pressure approaches the upstream pressure within a
predetermined amount.
According to the present invention there is provided in combination,
two duplicate check valve assemblies connected in series and defining a zone
between them; each check valve assembly having a stationary annular valve
~ ~,
.. . .. . . .
:. .. .. , ,, ., ~' ~
,,: . - , ~ , :
109~75
seat, a stationary barrel positioned coaxially of said valve seat and
having an internal cylindrical surface larger in diameter than that of said
valve seat, a valve poppet mounted for axial sliding movement in said
cylindrical surface and having a seal element adapted for sealing contact
with said valve seat, means cooperating with said barrel and said valve
poppet to define a chamber remote from said valve seat, a spring acting to
move said valve poppet into sealing contact ~ith said valve seat, means on
said valve poppet and said barrel for establishing a localized zone of
relatively rapid flow and consequent reduced pressure when forward flow
occurs through the check valve assembly, and port means on said poppet for
establishing communication between said localized zone and said closed
chamber to cause a reduction of pressure in said chamber to oppose the
action of said spring, and means including a control valve for venting said
zone to atmosphere, said control valve having means responsive to differen-
tial pressure across the upstream check valve assembly for actuating said
control valve.
Preferably said valve poppet includes axially spaced flanges, said
flanges defining a groove between them and one of the flanges having at
least a portion thereof extending into a discharge passage so that the
groove communicates therewith, said port means connecting each groove to
its respective chamber.
Preferably also, the differential pressure responsive means includes
a first port sensitive to both static and dynamic heads in the inlet passage
to the upstream check valve assembly, and also includes a second port sensi-
tive to substantially reduced pressure in the outlet passage of the up-
stream check valve assembly.
In a preferred embodiment the control valve includes a housing
~ provided with a valve seat, a stem mounted to ve axially in the housing
,. ~,
~ _ - 2
- -
1090~;75
and having a valve head movable to close against said seat, a cover, a
flexible diaphragm having its periphery clamped between the cover and the
housing and acting to define a chamber in the housing and a chamber in the
cover, means connecting the central portion of the diaphragm to the stem,
a spring in the cover chamber acting to move the stem in a direction to open
the valve, a discharge port in the zone connected to said housing, a pressure
sensing line connecting the housing chamber to the upstream side of the
upstream check valve assembly, and a pressure sensing line connecting the
cover chamber to the downstream side of said upstream check valve assembly,
and a balance piston fixed on the stem slidably mounted within the housing
to balance the fluid pressure force from the zone port tending to move the
valve head away from the valve seat.
Preferably said pressure sensing lines each have a port sensitive
to both static and dynamic heads, wi.th the upstream sensing port subjected
to a substantially greater total head than the downstream sensing port.
.
,, - '', .
.
~ ' ~ . - ~ .. . .
109~1;7S
In the accompanying drawings:
Figure 1 is a side elevation showing a complete ~ackflow preventer
assembly embodying this invention.
Figure 2 is an end elevation of the device shown in Figure 1.
Figure 3 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 4 is a sectional view showing a modified form of differential
pressure control valve, the parts being positioned for normal forward flow.
Figure S is a view similar to Figure 4, the parts in position corres-
ponding to backflow conditions.
Figure 6 is a graph showing pressure loss plotted against flow rate
for the backflow preventer device shown in Figures 1, 2 and 3. One curve of
the graph relates to a deYice of three-quarter inch nominal size, and the
other curve relates to the one-inch nominal size.
Referring to the drawings, the double check valve assembly generally
designated 33 and shown in Figure 3 employs two duplicate check valYe assembl-
ies 10a and 10b. Each is provided with a stationary cylindrical barrel 12
2C having a concentric valve seat 18. A valve poppet 11 is mounted for axial
sliding movement within the stationary barrel 12 and carries a sealing element
13 for contact with the seat 18. A coil compression spring 17 acts to move
the valve poppet 21 toward closed position. When both check valves lOa and
lOb are open, flow occurs i~ the direction of the arrows from the inlet ter-
minal 34 through the ~one ~2 between the check valves an~ through the outlet
terminal 35.
Each check valve has a first 1ange 20 with a first annular surface
25 co-planar with the sealing surface of the seal ring 13 and extending
r~ _ 4
~ ~.
`
;7S
radially outward therefrom. The flange 20 also has a second surface 25a on
the other side of the flange which forms one side of groove 22. The wall
portion 12a of the inclined barrel 12 extends into the discharge passage 28
so that when flow takes place the discharge pressure is not reflected into
the spring chamber 24.
Flange 20 effectively serves as a separator betweeD the localized
region 25_ of relatively rapid flow and consequent reduced pressure, and the
discharge pressure in the outlet passage 28. A portion of the flange 20
protrudes into the region 25~, creating a restriction 77. The pressure is
thus lowered in groove 22 and this reduced pressure is reflected through
communicating port 23 to the chamber 24~
The backflow preventer assembly shown in Figures 1, 2 and 3 includes
a double check valve assembly 33 having its inlet terminal 34 connected to a
supply pipe 36 through a shutof valve 37 and a union coupling 38. The outlet
terminal 35 of the double 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 3, 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 ~ro~ the check valve
l~b.
Means are provided ~or moving t~e stem 49 to open or close the
valve 48, S0, and as shown in the drawings this means includes flexible
-- 5 --
,
:
. . , . ' :
1090~i7S
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
differential pressure across the diaphragm 54 is the same as the differential
pressure between the inlet passage 68 and the inlet passage 71.
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 fl~id pressure acting against the under-
side of the annular piston 64. The annular space abo~e the piston 64 and
within the housing 47 is vented to atmosphere through vent port 74.
In operati~n, the differential control valve 43 serves to ~ent
the zone ~etween the check valve assemblies lOa and lOb through the discharge
port 52 whene~er the downstream pressure approaches the upstream pressure
within a predeterminsd 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 3S, the differential
control ~al~e 4~ will open to permit fluid to flow from the zone port52 ~ough
the pipe 44 and through the open valve 48, 50 to atmosphere. The several
- 6
' , - ' .
109~7S
forces applied to the stem 49 in addition to gravity are the opposing
forces developed by inlet pressure reflected in chamber 65, outlet pressure
reflected in chamber 66, zone pressure at port 52 reflectet 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 10_ ~reflected through line 45) plus the
force of the spring 76, plus the effect of gravity, exceeds the inlet pressure
from passage 63 Creflected through line 46) acting in chamber 65. The balance
piston 63 has the same effectiYe area as that of the seat 48, plus that of
the communicating~stem 49, so that the pressure exerted on ths valve head ~0
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 prsvent 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 ~orce of the
spring 73 and by the effect of gravity.
The chart of Figure 6 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
inc~eases up to a~out 20 gallons per minute for the three-~uarter inch size,
and up to about 32 gallons per min~te for the one inch size.
In the modified form of differential control valve shown in Figures
- 4 and 5, an axial passage 75 in the stem 49_ replaces the cover port 69.
- 7 -
~ - . ... . . .. .
., ,,. . . . . : - , . -
.. . . .. . .
.': ~''' ., '' ' ' ' ' ' `
1090l;7S
This passage 75 and its side outlet port 76 establishes communication between
the cover chamber 66 and the discharge pipe 44. Only one sensing line 46 is
used, and it connects the chamber 65 through line 46 to the inlet passage 68,
as described above. The sensing line 45 and port 70 are not used. Figu~e 4
shows the parts of the diaphragm control valve in closed position correspond-
ing to normal forward flow operation, and ~igure 5 shows the sa~e parts in
position to discharge fluid from the zone port 52 to atmosphere when bac~flow
conditions are present or imminent. In other respects, the construction and
operation of the modified form of the diaphragm control valve shown in
Figures 4 and 5 are the same as that previously described.
Having fully described our invention, it is to be understood that
we are not to be limited by the details herein set forth but that our invent-
ion is of the full scope of the appended claims.
-- 8 --
.
