WO2006047244A2

WO2006047244A2 - Plastic fiber wound pressure tank

Info

Publication number: WO2006047244A2
Application number: PCT/US2005/037807
Authority: WO
Inventors: Robert Lombari
Original assignee: Flexcon Industries
Priority date: 2004-10-21
Filing date: 2005-10-21
Publication date: 2006-05-04
Also published as: WO2006047244A3

Abstract

An expansion tank. The tank includes an outer shell, a flexible diaphragm disposed within the outer shell and having a peripherial rim region, an entrapment ring, and a backing ring. The entrapment ring and the backing ring are disposed to sandwich the peripheral rim region and a portion of the outer shell therebetween to create a substantially watertight seal between the peripheral rim region and the outer shell such that the diaphragm defines two fluidically isolated chambers within the outer shell.

Description

Plastic Fiber Wound Pressure Tank This application claims the priority of U.S. Provisional Application No. 60/620,744, filed October 21, 2005, the entire contents of which are incorporated herein by reference.

Field of the Invention This invention pertains to a diaphragm pressure tank.

Background of the Invention Expansion tanks are known for use in flow systems for controlling flow of liquid under varying pressures. Generally, expansion tanks comprise an essentially cylindrical or spherical housing containing a bladder-type diaphragm which divides areas of a liquid and a pressurized gas. For a general discussion of expansion tanks and bladder-type diaphragms, see U.S. Patent No. 4,784,181 to Hilverdink entitled "Expansion Tank with a Bladder-Type Diaphragm". U.S. Patent No. 3,035,614, the contents of which are incorporated herein by reference, describes a method of attaching a diaphragm to a metallic tank. An expansion tank has one nozzle through which liquid flows in and out depending on the pressure level controlled by the contraction and expansion of the interior diaphragm.

Summary of the Invention In one embodiment, the invention is an expansion tank. The tank includes an outer shell, a flexible diaphragm disposed within the outer shell, the diaphragm having a peripherial rim region, an entrapment ring, and a backing ring. The entrapment ring and the backing ring are disposed to sandwich the peripheral rim region and a portion of the outer shell therebetween to create a substantially watertight seal between the peripheral rim region and the outer shell such that the diaphragm defines two fluidically isolated chambers within the outer shell. The outer shell may include a first head having a first mating edge and a second head having a second mating edge, and the tank may be welded at the first and second mating edges. For example, the first and second mating edges may be welded to one another. The tank may further include a cylindrical side wall having third and fourth mating edges, and the first mating edge may be welded to the third mating edge while the second mating edge is welded to the fourth mating edge. The second head may include a wall portion and an inlet portion and a threaded insert in interlocking mechanical communication with the wall portion. The inlet portion may be injection molded around the threaded insert. The threaded insert may at least partially define a path for water to flow into and out of the tank, and the tank may further include a perforated retainer disposed in the path through which water flows into the tank. The expansion tank may further include an outer layer disposed about the outer shell and the backing ring, which outer layer includes a substantially continuous winding of glass fiber and an epoxy. The expansion tank may further include a charge valve to adjust a pressure in a space between the outer shell and the bladder. The outer shell may include one or more of polypropylene, DelrinTM, TeflonTM, nylon, polyalkylene terephthalate, polyformaldehyde, polystyrene, poly(methyl methacrylate), polycarbonate, and poly(hexylisocyanate). The diaphragm may include one or more of isobutylene, polybutadiene, poly(dimethylsiloxane), poly(cis- 1 ,4-isoprene), poly(trans- 1 ,4-isoprene), and thermoplastic elastomers. In another aspect, the invention is an expansion tank. The tank includes an outer shell, a flexible diaphragm disposed within the outer shell and dividing the interior of the outer shell into two fluidically isolated chambers, and an insert disposed in the outer shell that at least partially defines a path for water to flow into the bladder from outside the tank. At least a portion of the outer shell is injection molded around the insert. The expansion tank may further include a perforated retainer disposed in the path through which water flows into the tank. The insert may be threaded and/or may include a fiber-reinforced composite.

Brief Description of the Drawing The invention is described with reference to the several figures of the drawing, in which, Figure 1 is a schematic diagram of a pressure tank according to an embodiment of the invention. Figures 2 and 3 are expanded views of a portion of Figure 1.

Detailed Description of Certain Preferred Embodiments Figure 1 is a schematic diagram of a diaphragm tank 10 including shell 12 and diaphragm 14. Shell 12 includes central tube 16 and first and second heads 18 and 20, respectively. The caps are spin welded to central tube 16 to form shell 12. One skilled in the art will recognize that first and second heads 18 and 20 may be elongated to the point where they may be spin welded to each other to form a shell, obviating central tube 16. First cap 18 may include charge valve 22 for adjusting the pressure inside the tank. Second cap 20 includes a water connector 24 via which water flows into and out of the tank. Water connector 24 may be spin welded directly to the wall of second cap 20. Some exemplary water connectors that may be adapted for use with the invention include those disclosed in 4,784, 181 , in U.S. Patent Application No. 10/828,980, in U.S. Patent No. 6,264,247, and in U.S. Patent Application No. 1 l/xxx,xxx, filed with Express Mail No. EV782615529US, the entire contents of all of which are incorporated herein by reference. In another embodiment, water connector 24 may be injection molded as part of second cap 20 (Figure 2). For example, an inlet portion 20a may be injected molded around a threaded insert 20b, which may be prepared from the same material or a fiber reinforced polymer. Indeed, the matrix material of the fiber reinforced insert may be the same polymer as the inlet portion 20a of the second head 20. The insert 20b may be fabricated with a chamfer 21, for example, at 45°, that can receive an o- ring 40, which provides a seal between external water connection 42 and threaded portion 20b, obviating the use of plumber's caulk or Teflon tape, either of which might shed fragments into the tank that would mix with the water (Figure 3). A perforated retainer 44 inserted into the threaded insert 20b prevents extrusion of diaphragm 14 into the interior of water connection 24 (Figure 3A). The shell 12 is produced from a polymer that is relatively stiff. When the tank 10 is used to hold potable water, the polymer is preferably suitable for use with food or is non-toxic, non-carcinogenic, and non-mutagenic and does not leach such materials into the water. The polymer may be approved for use with food by an appropriate government agency. The polymer may also be resistant to degradation by chlorine, fluorine, ozonated water, sulfur, or other chemicals that may be found in well water or municipal water. In other embodiments, the tank is used in a hot water circulation system, in which potability is not a concern but in which it is more important that the tank material withstand high temperatures (150-200⁰F). Exemplary materials for use in producing the shell 12 include but are not limited to polypropylene, Delrin™, Teflon™, nylon, polyalkylene terephthalate, polyformaldehyde, polystyrene, poly(methyl methacrylate), polycarbonate, and poly(hexylisocyanate). Exemplary polypropylene materials for producing the shell include P6E5A-004 polypropylene impact copolymer, available from Huntsman. The diaphragm 14 may be produced from a resilient, flexible polymer. When the tank is used to hold potable water, the polymer is preferably suitable for use with food or is non-toxic, non-carcinogenic, and non-mutagenic and does not leach such materials into the water. The polymer may be approved for use with food by an appropriate government agency. The polymer may also be resistant to degradation by chlorine, fluorine, ozonated water, sulfur, or other chemicals that may be found in well water or municipal water. In other embodiments, the tank is used in a hot water circulation system, in which potability is not a concern but in which it is more important that the bladder material withstand high temperatures (150-200⁰F). Exemplary materials for use in producing the flexible diaphragm 34 include but are not limited to isobutylene, polybutadiene, poly(dimethylsiloxane), poly(cis-l,4- isoprene), poly(trans-l,4-isoprene), and thermoplastic elastomers. Figure 4 shows a schematic view of how diaphragm 14 attaches to the wall of tank 10. The interior diameter of diaphragm 14 is about equal to the outer diameter of entrapment ring 30, such that the edge of diaphragm 14 fits snugly inside entrapment ring 30. The outer diameter of diaphragm 14 is about equal to the inner diameter of tube 16, such that the diaphragm does not need to be stretched or crimped to be attached to tube 16. After diaphragm 14 and entrapment ring 30 are disposed within tube 16, backing ring 32 is disposed outside of tube 16 to sandwich the diaphragm 14 and the wall of tube 16 between backing ring 32 and entrapment ring 30. The backing ring is crimped from the inside or outside of the shell to create a seal between two cavities in the shell 12, separated by diaphragm 14. Entrapment ring 30 is sufficiently stiff to oppose the pressure of the crimping without buckling. In one embodiment, backing ring 32 is manufactured as a flat hoop (e.g., thin cylinder) and takes on the convexity seen in the figures during assembly of the tank, while entrapment ring 30 is manufactured with the convexity seen in the figure. Figure 2 shows that there is a groove 34 in the wall of tube 16. This groove is formed by the force of crimping backing ring 32. After the backing ring is crimped and diaphragm 14 sealed against tube 16, the heads are spin welded to tube 16 to close shell 12, and the entire shell is wrapped with fiberglass and an epoxy resin. One skilled in the art will recognize that one of the heads may be welded to tube 16 before the diaphragm 14 is attached. If the two heads and the shell are plastic, the assembled tank 10 may be wound with continuous glass fiber and epoxy resin, for example, a mixture of EPON™ and EPIKURE™, both available from Resolution Performance Products, to reinforce the walls. Shell 12 may also be fabricated as described in U.S. Patent Publication No. 2003/0111473, the entire contents of which are incorporated herein by reference. In one embodiment, in order to prevent the diaphragm 14 from fully closing the aperture 34 of the second head 20 when the liquid is expelled from the tank 10, the diaphragm 14 is provided on the inside, at the point opposite the aperture 34, with a number of raised pads 36 (Figure 5), between which the liquid can flow from the aperture 34 into the tank through grooves 38. The pads 36 prevent the development of a vacuum between the diaphragm and the interior surface of shell 12. Figure 1 shows the diaphragm 14 in its collapsed state. When liquid enters the tank 10, it exerts pressure on the inside of the diaphragm and causes it to expand away from second head 20. This expansion compresses the gas in the space between the flexible diaphragm 14 and the outer shell 12. When the liquid pressure is less than the pressure of the gas, the gas expands and pushes against the diaphragm 14, causing it to collapse against shell 12 and expel the liquid. The operation of diaphragm expansion tanks is well known to those skilled in the art and is described in U.S. Patent No. 4,784,181. Because the shell 12 is plastic, not metal, no liner is necessary where the tank is used for water. Flexible diaphragm may be produced in a bowl shape, as shown in Figure 1, or in an inverted bubble shape, as shown in Figure 6. The bubble shape facilitates production of flexible diaphragms for narrower, more elongated tanks. Once the bladder and tank are assembled and pressurized, the convex projecting portion of the flexible diaphragm is inverted so that the collapsed bladder takes on the bowl shape shown in Figure 1. The use of polypropylene or similar materials to form shell 12 provides several advantages. It prevents rubber from rubbing against rubber in operation, for example, as the diaphragm expands and deflates with respect to second head 20. Polypropylene, Teflon, etc., are lubricious, reducing friction as the diaphragm deflates and expands, extending the life of the diaphragm and allowing the tank to be constructed less as a set of paired hemispheres and with more of an oblong shape. This allows the tank to take on a more cylindrical shape, providing increased capacity with a smaller footprint. In addition, second head 20 provides additional stability to the diaphragm 14 as it expands during use. In larger tanks, the diaphragm does not always expand symmetrically as the bladder is filled. The second head prevents the compliance of the flexible diaphragm from magnifying initial asymmetries in filling. Where the tank is used to hold potable water, it is desirable to promote circulation of water through the tank 10 so that water enters and leaves the bladder on a "first-in-first-out" (FIFO) basis rather than a "last-in-first-out" (LIFO) basis. Even if the circulation of water is imperfect, that is, water enters and leaves the bladder on some combination of FIFO and LIFO, increased circulation reduces the time that water is resident in the bladder and prevents the water from becoming stagnant. Exemplary flow diverters that may be used to promote water circulation include those disclosed by U.S. Patent No. 6,343,622, U.S. Patent Application No. 10/828,980, and other diverters known to those skilled in the art. In other embodiments, the tank 10 may be employed in a hot water circulation system, for example, for heating a home or other space. Other embodiments of the invention will be apparent to those skilled in the art from a consideration of the specification or practice of the invention disclosed herein. What is claimed is:

Claims

1. An expansion tank, comprising: an outer shell; and a flexible diaphragm disposed within the outer shell, the diaphragm having a peripherial rim region; an entrapment ring; and a backing ring, wherein the entrapment ring and the backing ring are disposed to sandwich the peripheral rim region and a portion of the outer shell therebetween to create a substantially watertight seal between the peripheral rim region and the outer shell such that the diaphragm defines two fluidically isolated chambers within the outer shell.

2. The expansion tank of claim 1, wherein the outer shell comprises a first head having a first mating edge and a second head having a second mating edge, and wherein the tank is welded at the first and second mating edges.

3. The expansion tank of claim 2, wherein the first and second mating edges are welded to one another.

4. The expansion tank of claim 2, further comprising a cylindrical side wall having third and fourth mating edges, and wherein the first mating edge is welded to the third mating edge and the second mating edge is welded to the fourth mating edge.

5. The expansion tank of claim 2, wherein the second head comprises a wall portion and an inlet portion and a threaded insert in interlocking mechanical communication with the wall portion.

6. The expansion tank of claim 5, wherein the inlet portion is injection molded around the threaded insert.

7. The expansion tank of claim 5, wherein the threaded insert at least partially defines a path for water to flow into and out of the tank, and wherein the tank further comprising a perforated retainer disposed in the path through which water flows into the tank.

8. The expansion tank of claim 1, further comprising an outer layer disposed about the outer shell and the backing ring, the outer layer comprising a substantially continuous winding of glass fiber and an epoxy.

9. The expansion tank of claim 1, further comprising a charge valve to adjust a pressure in a space between the outer shell and the bladder.

10. The expansion tank of claim 1, wherein the outer shell comprises one or more of polypropylene, Delrin™, Teflon™, nylon, polyalkylene terephthalate, polyformaldehyde, polystyrene, poly(methyl methacrylate), polycarbonate, and poly(hexylisocyanate).

11. The expansion tank of claim 1 , wherein the diaphragm comprises one or more of isobutylene, polybutadiene, poly(dimethylsiloxane), poly(cis- 1 ,4-isoprene), poly(trans- 1 ,4-isoprene), and thermoplastic elastomers.

12. An expansion tank, comprising: an outer shell; a flexible diaphragm disposed within the outer shell, the diaphragm dividing the interior of the outer shell into two fluidically isolated chambers; and an insert disposed in the outer shell, the insert at least partially defining a path for water to flow into the bladder from outside the tank, wherein at least a portion of the outer shell is injection molded around the insert.

13. The expansion tank of claim 12, further comprising a perforated retainer disposed in the path through which water flows into the tank.

14. The expansion tank of claim 12, wherein the insert is threaded.

15. The expansion tank of claim 12, wherein the insert comprises a fiber-reinforced composite.