FIELD OF INVENTION
The invention relates to a dual plate check valve. This valve is used in pipe lines/piping systems to allow flow in one direction and prevent reversal of flow of fluid. The valves are self operated, i.e., the fluid in the pipe line operates the valve depending upon fluid momentum. The plates are opened by the differential pressure across the plates and then kept in partially or fully opened position by the dynamic fluid momentum exerted by the fluid on the plates.
Dual plate check valve consists of an annular housing body. This body has an up stream end and down stream end with a through passage. There are two substantially semicircular openings. These openings are formed by providing an integral diameteral beam in the passage of the body. Two substantially semi-circular plates known also as flaps or flappers, may be of D shape are provided to effectively close the openings. These plates are hinged in one or two hinge pins and loaded with a spring. Plates movement more than 90° is stooped by a stop pin. The stop pin may be provided parallel to and down stream of the hinge pin. Each end of the hinge pin and stop pin is inserted in socket provided in a holder. The present invention arrests the movement of the holder.
PRIOR ART
In the prior art hinge pin and stop pins are fitted on the valve body by diametrically opposite radial holes on the body, these holes are closed by pipe plugs called retainer.
US 4694 853 teaches a wafer check valve having an annular housing , closing flaps effective to close a passage through the housing and spring urged to a passage closing position, the flaps being mounted on one or more hinge pins, the or each pin extending to each end into bore in an insert, the inserts being received in the respective slots in the body and including means retaining the inserts in the slots without movement. The means retaining inserts is a L shaped ring which is fitted into groove at the down stream end of the body. Slots extend from the groove. The ring has a smaller outer radius than the external radius of the body and is held in position in the valve body by screws.

In the above referred U. S. patent, the inserts are retained in the slot formed in the housing with out movement by a L shaped rings. This ring give problems at the time of assembling in the pipe line or very accurate machining is required for groove in the housing as well as of the ring and proper fixing of screws.
EP 0753 116 teaches a dual plate check valve comprising an annular housing and two closing flaps effective to close a passage through the housing, the flaps being mounted on one or more hinge pins, each of the hinge pin extending at each end into a socket in an insert, the inserts being received in the respective open sided recess in the annular housing characterized in that each said insert is retained in a recess by means of a respective keeper plate located in a generally radially outwardly extending slot formed in said annular housing, and said keeper plate is retained in said radial slot by means of retaining screws, dowels pins, pegs, or clips located in bores in said annular housing and extending into or through corresponding bores formed in said keeper plate.
In the above mentioned European patent, the inserts are retained by a keeper plate being fixed in a slot formed in the housing and in the inserts and retained with the help of screws, dowels, pins or clips. Machining of said slot is cumbersome and gives problem in assembling.
The present invention over comes all of the above referred problems in the prior art.
OBJECTS OF INVENTION
The main object of the present invention is to provide leakage free dual plate check valve to prevent leakage of fluid from fluid path in the valve chamber to environment.
Another object of the invention is to provide a dual plate check valve with an easily replaceable and cheap to manufacture wear part used in the dual plate check plate valve assembly.

Another object of the invention is to provide a dual plate check valve with full gasket face conforming to international standards at both up stream and down stream sides for such valves.
Another object of the invention is to provide a dual plate check valve which is simple to machine and is cost effective.
Further object of the invention is to provide a means to prevent all radial and axial movements of holder.
Further object of the invention is to provide socket head screw to prevent any movement of locking plate.
STATEMENT OF THE INVENTION
According to the present invention, there is provided a dual plate check valve, which comprises a annular valve body having up stream and down stream end, a through passage with two substantially semi-circular openings, two substantially semi-circular plates to effectively close the said two openings, the said plates being hinged on at least one hinge pin and loaded with a spring and a stop pin to prevent the plate from toppling over, two diametrically opposite slots extending radially outward in the passage and axially up to down stream end of said valve body, two holders sliding received in respective slots, each holder having at least two sockets, one for retaining hinge pin and the other for retaining the stop pin, each holder after assembling at each end of the said hinge pin and stop pin fitted slidingly in respective slot and means to prevent axial movement and radial movement of said holders, characterized in that the means to prevent the axial movement of each holder is a locking plate received in the recess surrounding said slot on said down stream end, each locking plate being fixed to the said body with one or more screws, and either said slot and holder or said holder and locking plate being configured to prevent radial movement of the holder.

BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
The invention will more clearly be understood from the following description which is given by way of preferred example only with reference to the accompanying drawings, and not to limit the scope of the invention, wherein:
FIG. 1 and FIG. 2 shows the isometric view of embodiments of the invention.
FIG 3, 4, 5 shows cross sectional view, detailed cross sectional view and plan view of embodiment where the holder and slots has cross section substantially semi circular and segment shaped locking plates having a step recess to match the projection in the holder.
FIG 6,7,8 shows cross sectional view, detailed cross sectional view and plan view of embodiment where the holder and slots has cross section substantially semi circular and segment shaped locking plates having a tapered recess matching the tapered projection in the holder.
FIG 9,10,11 shows cross sectional view, detailed cross sectional view and plan view of embodiment where the holder and slots has cross section substantially semi circular and rectangular shaped locking plates having a step recess to match the projection in the holder.
FIG 12,13,14 shows cross sectional view, detailed cross sectional view and plan view of embodiment where the holder and slots has cross section substantially semi circular and rectangular shaped locking plates having a L cross section.
FIG 15,16,17 shows cross sectional view, detailed cross sectional view and plan view of embodiment where the holder and slots has more than half round cross section and a substantially semi circular cross section locking plates.
FIG 18,19,20 shows cross sectional view, detailed cross sectional view and plan view of embodiment where the holder and slots has a Dow tail cross section substantially semi circular cross section locking plates.

DETAIL DESCRIPTION WITH REFERENCE TO DRAWINGS
The invention is described with reference to the accompanying drawings by way of example not to limit the scope of the invention.
A dual plate check valve has an annular valve body (1) with up stream end (15) and down stream end (16). A through passage (17) with two substantially semi-circular openings is provided in the passage of the valve body (1). These said two openings are having seat for effectively closing with out leakage by substantially semi-circular D shape plates (2). These plates are hinged on at least one hinge pin (5) and loaded with a spring (7). One hinge pin for one plate or both hinge plates can be hinged on one hinge pin. A stop pin (6) is also provided to prevent the plate from toppling over i.e., to restrict the movement of the hinge plate by not more than 90°. Two diametrically opposite slots (10) extending radial outwardly are provided in the passage (17) and these slots are axially up to down stream end (16) of said valve body (1). Two holders (8) are sliding received in respective slots (10). Each holder (8) has at least two sockets (9), one for retaining hinge pin (5) and the other for retaining the stop pin (6). Each holder (8) after assembling each end of the said hinge pin (5) and stop pin (6) are fitted slidingly in respective slot (10). These holders are prevented axial movement and radial movement by a suitable means. The preferred means to prevent the axial movement of each holder (8) is a locking plate (11), which is received in the recess (12), surrounding the said slot (10) on said down stream end. Each locking plate (11) is fixed to the said body with one or more screws (13). The shape of said slots (10) and holders (8) are having a particular shape so as to prevent radial movement. The radial movement can further be prevented by having a particular shape of locking plates (11) and the holders (8).
Each of the said holder (8) may have a cross section substantially lying between a semicircle and a circle when viewed axially and the slot (10) has a matching opening for slidingly receiving the holder in the slot and to prevent radial movement of the holder. In another embodiment each slot and holder can be configured in dove-tail shape for slidingly receiving the holder in the slot and to prevent radial movement of the holder.

Top surface of the holder (8) and the abutting surface of the locking plate (11) may be plane. Axial movement is prevented by the locking plate (11) in both embodiments.
Each holder (8) can be configured to have tapered surface) on its down stream end, and locking plate also can be configured to have corresponding matching tapered recess to prevent radial movement of the holder in another embodiment. Both holders (8) can be configured to have step projection on its downstream end and the locking plate may be configured to have a corresponding matching recess (14) to prevent radial movement of the holder in another embodiment. Each holder (8) can be configured to have a flat surface on its downstream end and the locking plate can be configured to have a L shaped projection which overlaps the outer side of the holder in the passage and to prevent radial movement of the holder in yet another embodiment. Each said holder can be configured to have a projection on its down stream end, and the locking plate can be configured to have a corresponding matching recess to prevent radial movement of the holder in another embodiment. Each of the said holders can be configured to have any shape of recess on its downstream end and the locking plate can be configured to have a corresponding matching projection to prevent radial movement. All of the above said embodiments may have substantially semicircular shape of the slot when viewed axially and corresponding matching cross section of the holder.
The locking plate (11) of any embodiment may have a sector of circular shape or rectangular shape, which is fixed in the matching recess in the valve body.

We claim:
1. A dual plate check valve comprising an annular valve body, having an up-stream
end and a down-stream end, a through passage with two substantially semi-circular
openings, two substantially semi-circular plates to effectively close the said two
openings, the said plates being hinged on at least one hinge pin and loaded with a spring
and a stop pin to prevent the plate from toppling over, two diametrically opposite slots
extending radially outward in the passage and axially up to down stream end of said
valve body, two holders slidingly received in respective slots, each holder having sockets
for retaining hinge pin and stop pin, said holders after assembling at each end of the said
hinge pin and stop pin fitted slidingly in respective slot and means to prevent axial
movement and radial movement of said holders, characterized in that the said means to
prevent the axial movement of each holder is a locking plate received in the recess
surrounding said slot on said down stream end, each locking plate being fixed to the said
body with one or more screws, and either said slot and holder or said holder and locking
plate being configured to prevent radial movement of the holder.
2. A dual plate check valve as claimed in claim 1, wherein each of the said holder
has a cross-section, substantially lying between a semicircle and a circle when viewed
axially and the slot has a matching opening for slidingly receiving the holder in the slot
and to prevent radial movement of the holder.
3. A dual plate check valve as claimed in claim 1, wherein each of the said slot and
holder is configured in dove-tail shape for slidingly receiving the holder in the slot and to
prevent radial movement of the holder.
4. A dual plate check valve as claimed in claim 1 wherein each of the said holder
has a cross section substantially in semi-circular shape, when viewed axially, said slot
has a matching opening for slidingly receiving the holder in the slot and said holder and
said locking plate are provided with means to prevent radial movement of the holder.
5. A dual plate check valve as claimed in claim 4, wherein each of the said holder is
configured to have tapered surface on its downstream end, and locking plate is

configured to have corresponding matching tapered recess to prevent radial movement of the holder.
6. A dual plate check valve as claimed in claim 4, wherein said holder is configured
to have step recess on its downstream end and the locking plate is configured to have a
corresponding matching projection to prevent radial movement of the holder.
7. A dual plate check valve as claimed in claim 4, wherein said holder is configured
to have a flat surface on its downstream end and the locking plate is configured to have a
L shaped projection to over lap the outer side of the holder facing the passage to prevent
radial movement of the holder.
8. A dual plate check valve as claimed in claim 4 wherein each said holder is
configured to have a projection on its downstream end, and the locking plate is
configured to have a corresponding matching recess to prevent radial movement of the
holder.
9. A dual plate check valve as claimed in claim any of the preceding claims wherein
the said locking plate is a segment of a circular shape and is fixed in the matching recess
in the valve body.
10. A dual plate check valve as claimed in claim any of the preceding claims 1-8
wherein the said locking plate is having a substantially rectangular shape and is fixed in
the matching rectangular recess in the valve body.
11. A dual plate check valve as described herein before and illustrated with reference
to the accompanying drawings.