IL45802A - Check valve useful in backflow prevention apparatus - Google Patents

Abstract

1490553 Valves GRISWOLD CONTROLS 25 Oct 1974 [26 Oct 1973] 46301/74 Heading F2V In a check valve a closure member 10 is biased by a spring 17 towards a seat 18 and is provided with spaced guiding flanges 20, 21 which move in barrel 12. The flange 20 projects into the outlet passage 28 to provide a throttle 77 the reduction in pressure in which is communicated via groove 22 and passage(s) 23 to a chamber 24 to assist in opening the valve. Two such check valves may be used in series to form a back flow preventer, Fig. 9, which has the chamber 52 between the check valves vented via line 44 and valve 50 when the pressure differential across the upstream check valve falls to a predetermined value which is sensed by ports 67, 70 and is transmitted via passages 45, 46 to the opposite sides of a diaphragm assembly 54 to actuate the valve 50. In a modification the passage 45 is replaced by an axial passage (75) in the valve stem 61 communicating with the line 44. [GB1490553A]

Description

45802/2 i /mm no' t/ ny»aaV jpnna wawan ayu nw oinor? Check valve useful in baekflow prevention appaxatue GRISWOLD CONTROLS C. 43819 This invention relates to fluid flow apparatus and is particularly directed to improvements in check valve cons 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 then. 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, oven under vacuum conditions 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 satis factorial ly , 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. Unfortunately, this often results, in a pressure drop of serious proportions, 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.

Accordingly, it is the principal objective of this invention to provide check valves suitable for use in backflov;-'prevention equipment and that are constructed to both provio a relatively high initial resistance to pressure and flow and yet as the demand for flov; increases, cause the corresponding pressure drop to be at a minimum value.

Another 'Important object is to combine a pair of series - connected check valves of this type with a novel form of differential control valve for venting the zone between the check valves to atmosphere when the downstream pressure approache the upstream pressure within a predetermined amount.

Other and more detailed objects and advantages "will appear hereinafter.

In the drawings : 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 c eck 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 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 coaxial.

Figure 5 is a sectional elevation showing a preferred form of double check valve assembly, both check valves being shown in closed position.

Figure 6 is a graph showing jircssurc 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- 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 is a graph showing pressure loss plotted against flow rate for the backflow preventer de\rice 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 bein 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 hown 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 oppet 11 by means of a retaining washer 14 and a threaded fastenin 15.

A coil compression spring 17 acts on the poppet 11 to bring the resilient ring 13 into sealing engagement with the statH^-^ ary annular seat 18 provided at the end of the inlet passage 19.

The poppet 11 lias a first flange 20 and a second flange 21 both slidablv 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 pi ure 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 terminal 26a and the outlet terminal 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 27£ 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 IS and the resilient ring 13 into the outlet passage 28. Inlet presssure 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 serves as a seal between the pressure area 29 and pressure area 22. In Figure 4, stationary housing 30 encircles the barrel 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 of the stationary seat 18, so that when the check valve is in closed position with the resilient ring 13 engaging the seat the pressure in the inlet passage 19 acts over a subs tantiall> 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 corresponding to forward flow operation, as shown in Figures 1-4, the flow of the fluid creates a low pressure region around thepoppet 11 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 19, 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 described, as the velocity of forward flow increases, the velocity head products a positive opening force on the poppet 11 on the side containing the resilient ring 13 together with* a lo ering, 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 flew increases , the velocity lie ad acting upon the full effective area of flange 20 (on the side with the resilient seal) increases. Vith 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 rret result is an advantageous pressure differential 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 barrel 12 with adequate clearances to avoid mechanical fractional losses to minimize mechani cal 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, sho in Figure 5, employs two duplicate c eck valve assemblies 10a a d 10b which are substantially the same as the check valve 10 described in detail above. These check valve assemblies are arranged at rieht ancles, the check valve 10a assembly beinr positioned at 45° to the axis of the inlet terminal 34 and the check valve assembly 10b being at 45° to the axis of the terminal 35. The construction and operation of each of these check valve assemblies 10a and 10b is the same as that of the check valve assembly 10 described above. Moreover, the geometri relationship of the assemblies 10a and 10b as shown in Figure 5 produces a uniform flow pattern by minimizing the extent of 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 valve assembly of Figure 5, for both the nomina size of three-quarter inch and the nominal siz.e of one inch. It will be observed that the pressure loss through the assemblies 10a 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 chec valve assembly 10a and 10b 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 supply 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 thereo protruding into its respective discharge passage, or in communication with its dicharge passage, so as to be responsive to the slightest reverse flow action, closing spontaneously to prevent backflo .

The backflow preventer assembly shown in Figures 7, 8» and 9 include a double, check valve assembly 33 having its inlet t a s l i e 36 throu h a shutoff val check valve assembly 33 is connected through union coupling. 39 and shut off valve 40 to the service pipe 41. Λ control valve assembly 43 is connected to the " double check valve assembly 35 by means of discharge pipe 44 and pressure- sensing lines 45 and 46. The discharge pipe 44 froms a portion of the stationary housing 47 which contains a removalbe valve seat 4.8. 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 10b.

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 flanpc 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 53 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 6S of the check valve assembly 10a_. The chamber 66 is connected through cover port 69, passage 45 nnd port 70 with the inlet passage 71 for the check valve assembly 10b. 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 The coil compression spring 73 in the chamber 6G acts on the d ianhra vm plate 5S to move the stem 49 in a direction to open the discharge valve 4S, 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 7 . ί In operation, the differential control valve 43 serves I to vent the zone between the check valve assemblies 10a_ and 10b \ through the discharge port 52 -whenever the downstream pressure I approaches the upstream pressure within a predetermined amount.

'; Thus for example, the ports may be designed and adjusted so that i " when the pressure in the inlet terminal 34 is less than t o-PSI greater than the pressure in the outlet terminal 35, the differential 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 reflected 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 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 10a. (reflected through line 45) plus the force of the spring 76, plus the effect of gravity, 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 exerted on 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 described 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 presen or imminent. In other respects, the construction and operation of Having fully described our invention, it is to be understood that we are not to be limited by the details here* set forth but that our invention is of the full scope of the appended claims. 45802/2

Claims (11)

1. In a check valve, the combination of: means forming an inlet passage terminating in a stationary inclined annular valve seat, an inclined stationary barrel positioned 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 at least one of said flanges projecting into said discharge passage to create a zone of relatively rapid flow and consequent reduced pressure, 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.

2. The combination set forth in Claim 1 in which said barrel is coaxial with but larger than said valve .seat.

3. The combination set forth η Claim 1 in which the spring comprises a coil compression spring mounted within said chamber.

4. The combination set forth in Claim 1 in which the inlet passage is provided with an inlet terminal and the outlet passage is provided with an outlet terminal.

5. The combination set forth in Claim 4 in which said terminals are axially aligned.

6. The combination set forth in Claim 4 in which said terminals are axially aligned and the axis of movement of 45802/2

7. In a check valve, the combination of: means -informing an inlet passage terminating in a stationary annular valve seat, a stationary barrel positioned coaxially of the valve seat, 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 sea by fluid pressure in the inlet passage, said valve poppet having axially spaced flanges slidably guided within said barrel and defining an annular groove between tha¾ ,means forming a discharge passage, a portion of at least one of said flanges projecting into said discharge passage to create a zone of relatively rapid flow and consequent reduced pressure, means establishing communication between said zone and said annular groove , means cooperating with said barrel and said valve poppet to define a chamber remote from said valve seat, and port means connecting said groove to said chamber, whereby forward flow of fluid through the check valve causesaa reduction in pressure in the chamber to oppose the action of said spring.

8. In a check valve, the combination of: a stationary body having an inlet passage and a discharge passage, said inlet passage terminating in a stationary annular valve seat, said body having 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 having a seal element adapted for sealing contact with said valve seat, a flange on said poppet in sliding contact with said cylindrical surface, bias means acting to move said valve poppet into sealing contact with said valve seat, said bias means acting to create a pressure drop when said 45802/2 V 4 barrel and said valve poppet to define a chamber remote from said valve seat, said flange having a first surface co-planar with said seal element and cooperating with a portion of said walls to establish a localized zone of relatively rapid flow and consequent reduced pressure, said flange having a second surface on the opposite side of the flange from said first flange surface, said second flange surface being in communication with said chamber, a portion of said stationary walls acting to insure that only the pressure in said localized zone immediately adjacent said second flange surface is in communication with said chamber when the valve is in open position.

9. The combinatio set forth in Claim 8 in which the inlet passage has an inlet terminal and the discharge passage has a discharge terminal, said terminals being coaxial, the axis of the stationary barrel being inclined with respect thereto.

10. The combination set forth in Claim 8 in which two parallel flanges are provided on the valve poppet, said flanges defining an annular groove between them, and port means connecting said groove to said chamber.

11. The combination set forth in Claim 10 in which1 said bias means comprises a coil compression spring mounted within said chamber. For the A plicants PARTNERS