Check valves

1. A check valve comprising:

an annular housing defining a generally circular opening;

a plurality of radially extending arms extending across the circular opening from the centre of the valve housing to respective nodes at the periphery of the valve housing;

a plurality of cross arms extending between circumferentially adjacent nodes, thereby dividing the circular opening into a plurality of primary, generally triangular radially inner openings and a plurality of secondary, generally segment shaped radially outer openings;

a plurality of primary, generally triangular flapper elements for closing the primary openings;

a plurality of secondary, generally segment shaped flapper elements for closing the secondary openings

a plurality of mounting posts, a respective mounting post being arranged at a respective node; and

a plurality of hinge pins, each hinge pin being mounted between two circumferentially adjacent mounting posts; wherein

a primary flapper element and a secondary flapper element are hingedly mounted to each hinge pin for pivoting between a closed position in which they close their respective primary and secondary openings and an open position in which they permit flow through their respective primary and secondary openings.

2. The check valve as claimed in claim 1 , comprising four primary and secondary openings and four primary and secondary flapper elements.

3. The check valve as claimed in claim 1 , wherein the primary flapper elements are each symmetrical about a radial centreline (A) thereof.

4. The check valve as claimed in claim 1 , wherein the base end of a primary flapper element comprises a pair of mounting lugs for receiving an associated hinge pin.

5. The check valve as claimed in claim 4 , wherein the primary flapper element mounting lugs are arranged at opposed edges of the primary flapper element.

6. The check valve as claimed in claim 1 , wherein the secondary flapper elements are each symmetrical about a centreline (A) of each secondary flapper element.

7. The check valve as claimed in claim 6 , wherein the base end of a secondary flapper element comprises a pair of mounting lugs for receiving an associated hinge pin.

8. The check valve as claimed in claim 7 , wherein the secondary flapper element mounting lugs are arranged displaced inwardly from opposed sides of the secondary flapper element.

9. The check valve as claimed in claim 1 , further comprising a plurality of stops for stopping the primary and secondary flapper elements in their open positions.

10. The check valve as claimed in claim 9 , wherein the stops comprise respective stop bars extending between respective circumferentially adjacent mounting posts.

11. The check valve as claimed in claim 10 , wherein the stop bars are arranged vertically above the hinge pins.

12. The check valve as claimed in claim 10 , wherein the mounting posts are formed with bores for receiving the respective stop bars.

13. The check valve as claimed in claim 10 , wherein the mounting posts are formed with bores for receiving the respective stop bars.

14. The check valve as claimed in claim 13 , wherein the bores are blind bores.

15. The check valve as claimed in claim 1 , wherein the mounting posts are separate from the valve housing and mounted thereto by one or more fasteners.

16. The check valve as claimed in claim 15 , wherein the mounting posts are formed with bores for receiving respective stop bars.

17. The check valve as claimed in claim 1 , wherein the mounting posts are formed with bores for receiving the respective hinge pins.

18. The check valve as claimed in claim 17 , wherein the bores are blind bores.