Backflow preventer

1. A modular fluid arrangement comprising:

a modular strut having an inlet body and an outlet body and defining a modular cage receiving area therebetween;

a modular cage removably secured to said modular strut and received by the modular cage receiving area, said modular cage having a first open end and a second open end and defining an interior cavity, said modular cage further comprising an end piece defining a central opening and having an annular member extending therefrom, said end piece positioned adjacent said first open end of said modular cage such that said annular member is received within the interior cavity, wherein the interior cavity of said modular cage is in fluid communication with said inlet body and said outlet body of said modular strut; and

a first sealing gasket, a second sealing gasket and a third sealing gasket for fluidly sealing said modular cage within the modular cage receiving area, a first axis passing through the interior cavity said first sealing gasket positioned between an inlet surface of said inlet body and said end piece, wherein said first sealing gasket is positioned about the first axis, wherein a plane is defined at the adjacent abutting surface of the inlet surface and the end piece through which the first axis passes, said second sealing gasket positioned around said annular member of said end piece for fluidly sealing said annular member within the interior cavity of said modular cage such that said second sealing gasket seals about a cylindrical surface circumferentially about the first axis, and said third sealing gasket positioned between an outlet surface of said outlet body and said second open end of said modular cage and about the first axis, wherein a plane is defined at the abutting surfaces of the said outlet surface and said second open end through which the first axis passes, wherein:

said modular cage and said modular strut are free to expand and contract a predetermined distance in a telescoping action relative to one another in a longitudinal direction thereby maintaining a fluid seal therebetween, and

the interior cavity of said modular cage is adapted to receive at least one check valve.

2. The modular fluid arrangement of claim 1 , further comprising at least one check valve in the interior cavity of the modular cage.

3. The modular fluid arrangement of claim 1 , wherein the modular cage and the modular cage receiving area are sized relative to one another, such that the modular cage and the modular strut can move relative to one another in a longitudinal direction.

4. The modular fluid arrangement of claim 1 , wherein an outer surface portion of the modular cage has a wedge surface adjacent at least one of the first and second open ends to seat the modular cage in the modular cage receiving area of the modular strut.

5. The modular fluid arrangement of claim 1 , further comprising a pressure relief valve securely mounted to the exterior of the modular cage, the pressure relief valve having a valve arrangement having a first position and a second position, wherein in the first position, the valve arrangement provides fluid communication between the interior of the modular cage and exterior of the modular cage, and in the second position prevents fluid communication between the interior of the modular cage and exterior of the modular cage.

6. The modular fluid arrangement of claim 5 , wherein the pressure relief valve comprises a first interior chamber and a second interior chamber separated by a diaphragm and a passageway extending from the first chamber of the pressure relief valve to exterior of the pressure relief valve and the exterior of the modular cage, wherein with the valve arrangement in the first position, fluid communication is provided between the first chamber of the pressure relief valve and the passageway, and the modular cage further comprising a valve tap providing fluid communication between the interior of the modular cage and the first chamber of the pressure relief valve.

7. The modular fluid arrangement of claim 6 , further comprising at least one check valve in the interior cavity of the modular cage.

8. The modular fluid arrangement of claim 6 , wherein the modular cage further comprises a first port in fluid communication with the interior of the modular cage and the second interior chamber of the pressure relief valve.

9. The modular fluid arrangement of claim 6 , wherein the valve arrangement comprises the diaphragm having a first surface facing the first chamber and an opposite second surface facing the second chamber, with a hole interconnecting the first and second surfaces, a piston having a closed end and an open end, with the open end facing the second surface of the diaphragm, a spring in the piston housing, a valve guide having at least one prong mounted in the piston against the biasing action of the spring, and a valve seat having at least one hole secured in the open end of the piston to capture the diaphragm between the piston and the valve seat, with the at least one prong of the valve guide extending through the at least one hole of valve seat, and wherein with the valve arrangement in the first position, the diaphragm is biased away from the modular cage and distance between the valve seat and the exterior of the modular cage increases to provide fluid communication between the first chamber and the passageway, and, with the valve arrangement in the second position biasing action on the diaphragm is removed.

10. The modular fluid arrangement of claim 9 , wherein with the valve arrangement in the first position, a fluid passageway is provided from the interior of the modular cage, through the valve tap, into the first chamber, through the valve seat and valve guide, through the spring, and out of the pressure relief valve through the passageway.

11. The modular fluid arrangement of claim 10 , wherein the valve tap further comprises a seal mounted in a groove provided in the outer surface of the modular cage and a seal retainer to secure the seal in position, wherein with the valve arrangement in the second position, a spring guide engages a portion of the seal.

12. The modular fluid arrangement of claim 6 , wherein the valve arrangement comprises the diaphragm having a first surface facing the first chamber and an opposite second surface facing the second chamber, with a hole interconnecting the first and second surfaces, a piston having a closed end and an open end, with the open end facing the second surface of the diaphragm, a spring in the piston housing, and a valve seat having at least one hole secured in the open end of the piston to capture the diaphragm between the piston and the valve seat, and wherein with the valve arrangement in the first position, the diaphragm is biased away from the modular cage and distance between the valve seat and the exterior of the modular cage increases to provide fluid communication between the first chamber and the passageway, and with the valve arrangement in the second position, biasing action on the diaphragm is removed.

13. The modular fluid arrangement of claim 12 , wherein with the valve arrangement in the first position, a fluid passageway is provided from the interior of the modular cage, through the valve tap, into the first chamber, through the valve seat, over the spring, and out of the pressure relief valve through the passageway.

14. The modular fluid arrangement of claim 13 , wherein the valve tap further comprises a seal mounted in a groove provided in the outer surface of the modular cage and a seal retainer to secure the seal in position, the seal retainer having at least one prong extending away from the modular cage, and the valve seat having at least one hole, and wherein with the valve arrangement in the second position, a spring guide passes over the retainer and engages a portion of the seal.

15. The modular fluid arrangement of claim 1 , wherein the modular cage further comprises at least one tap extending from the modular cage and in fluid communication with the interior of the modular cage.