The double plate check valve is a versatile check valve that is stronger, lighter and smaller in size than traditional swing check valves or life check valves. The design of the double plate check valve is the result of an attempt to solve the problems associated with swing check valves and lift check valves. The double plate check valve uses two spring loaded plates hinged on a central hinge pin. When flow is reduced, the plates close under the action of the torsion spring, eliminating the need for reverse flow. This design offers the dual benefits of both no water hammer and no impingement. All of these features combined make the double plate check valve one of the most efficient designs available. It is also known as a silent check valve. The valve is designed to meet APS 594 as well as API 6D standards, excluding face-to-face dimensions for ANSI 125 cast iron valves in sizes 65mm (2½") to 300mm (12"). Double-plate check valves are available in a clamp-on design, a clamp-on design with flanges, and an extended design with flanges with the same face-to-face dimensions as swing check valves, in accordance with API 598.

Technical Specifications

Double plate check valves are designed and manufactured in strict accordance with international standards API 6D, API 594, ASME B16.34 or equivalent.

Conforms to standards and design features.

Designed and manufactured in accordance with API 6D, API 594, ASME B16.34 or equivalent standards.

P.T rating in accordance with ASME B16.34

Face-to-face dimensions in accordance with ASME B16.10

Flange ends conform to ASME B16.5

Butt-weld ends conform to ASME B16.25

Valve markings in accordance with MSS SP-25

Inspection and testing in accordance with API 598

Size range from 1/2" to 60".

Construction is one-piece union valve body

Pressure ratings from Class 150 to Class 2500, PN16 to PN420

End connections are flanged R.F or RTJ, clamp-on, full-convex and slotted

Available in a variety of body and spool materials including carbon steel ASTM A216 WCB, WCC; cast iron or ductile iron A126, GG25, A536 or GGG50, low carbon steel LCB, LCC, alloy steel WC6, WC9, C5, stainless steel CF8, CF8M, CF3, CF3M, duplex and super duplex steel A890 GR.4A, 5A or F51 , special materials Monel, Alu. bronze C95800, 95600, etc. Coatings can be supplied to increase corrosion or wear resistance. Hardfacing and weld overlays are also available. Seats are available with metal-to-metal or bubble seal resilience.

Optional bypass systems and counterweight assemblies are available.

Features

1. Small size, light weight, compactness and ease of maintenance.

2. Uses two torsion springs on each pair of valve plates. It closes the valve plates quickly and automatically.

3. The quick closing action prevents the medium from flowing back and eliminates the water hammer effect.

4. The valve has a short length, therefore, it is rigid and easy to install.

5. It is easy to be installed on horizontal or vertical laying pipelines.

6. The valve seals tightly in the pressure water test, no leakage.

7. It is safe and reliable in operation and has strong anti-interference ability.

8. The connection size of the flange conforms to GB4216-84 GB4216.84

9. The end size conforms to GB12221-89, ISO5752-82 standard. When the valve is installed on the horizontal pipe, the stem should be vertical to the horizontal plane. When installed vertically, the direction of water flow should be downward.

10. Clamped ends, flanged ends can be used, Welco valves can also be produced in sizes up to 56 inches, and the pressure will be higher than Class 600.

Structure principle

Check valve opening and closing parts rely on media flow and force to open or close by themselves, in order to prevent the backflow of media valve called check valve. Check valve belongs to the automatic valve category, mainly used in the medium one-way flow of the pipeline, only allow the medium to flow in one direction to prevent accidents.

Check valve according to the structure, can be divided into lift check valve, swing check valve and butterfly check valve three. Lift check valve can be divided into vertical and horizontal. Swing check valve is divided into single valve, double valve and multi-flap type. Butterfly check valve for straight-through, the above types of check valve in the form of connection can be divided into threaded connection, flange connection and welding three. Check valve is a valve that can automatically stop the backflow of fluid. The flap of the check valve opens under fluid pressure and the fluid flows from the inlet side to the outlet side. When the pressure on the inlet side is lower than that on the outlet side, the valve automatically closes under the action of fluid pressure difference and its own gravity to prevent the backflow of fluid.

The production method of valve plate of double plate check valve 

The double plate check valve is known to the public and includes an annular housing with two radially hinged, roughly semicircular or D-shaped valve members or plates framed on radially hinged pins. These plates hold the valve in a closed position where the plate closes a corresponding semicircular or D-shaped hole defined within the housing by means of a radial cross member. The plate is usually pushed into the closed position by a spring. The valve plate can be pushed into the open position by a given pressure value on the upstream side of the valve, and in the open position the plate is approximately parallel to the housing axis. The valve plate may be provided with a flange-shaped buffer protruding from a semicircular edge on the side of the plate that does not contact the seat around the semicircular opening. There is usually a stop pin parallel to the hinge pin, which also prevents the valve from turning more than 90° from the closed position.

This double-plate check valve is a non-return valve that opens according to a given pressure value on the upstream side, that is, according to the pressure applied to the plate through the semicircular opening. When the pressure decreases, the flow rate decreases and the plate is pushed into the closed position of the valve by the reverse pressure, in some cases with the help of a spring device. This double-plate check valve has many advantages over swing check valves that include a single plate or tangentially articulated flap. The double-plate check valve has found special application in the favorable aspects of lighter weight, compactness and faster closing response than the swing check valve.

Double-plate check valve plates are made of plastic or sheet metal for low pressure applications, while for high pressure applications, i.e. ANSI pressure class 300 (PN50) or higher, cast or forged metal plates are generally used.

The known application limitation of double plate check valves that rely on metal-to-metal sealing compared to other check valves is their backflow leakage performance.

This limitation has been identified in international and national standards, such as API 598, which allows metal-seated double-plate check valves to have greater leakage than other types of valves, such as swing check valves with metal seats that can have zero leakage. Backflow leakage in some applications can be solved by placing elastomeric seals on the valve seat, but for other applications, such as low temperature or high temperature use, this solution is not applicable.

Double plate check valves have been in use for over 30 years and the harmful backflow leakage properties of these check valves are well understood, featuring two D-shaped seats on the body and two separate D-shaped plates that rotate around a hinge pin.

The backflow leakage properties are due to the backpressure on the D-shaped valve plates. In particular, it is believed that the backpressure increases the force acting on the center of pressure, which is on the centerline at about 1/3 of the diameter of the D-shaped plate, thus causing the D-shaped valve element to bend or deflect. The effect of deflection is uneven and is greatest at the corners or ring edges of the D-shaped valve plate and occurs first at the point of leakage.

The use of increased back pressure in high-pressure fluid equipment is dedicated to reducing leakage, and existing thin-plate check valves use methods that increase the thickness of the plate in the seat area and increase the stiffness, for example, by increasing the cross-sectional area of the radial rod and the perimeter seating area. The aim is to provide maximum stiffness against distortion using back pressure, trying to maintain as much contact as possible between the plate and the seat, especially in the "ring edge" area. This means increasing the amount of material in the valve plate for high pressure applications. This raises the cost. In addition, the use of thicker plates reduces the flow area and increases the pressure drop across the valve. The heavier weight seal plates, primarily used in high pressure large size valves, also increase friction and wear on the valve plate at the hinge, reducing valve performance and increasing closure response time. These performance reductions increase the likelihood of valve plate impact closure, increasing wear, noise and possible destruction of other piping equipment.

To provide a metal plate for a double plate check valve comprising a substantially D-shaped plate member with straight edges and means for framing said plate so as to rotate about an axis parallel and adjacent to said straight edges, said plate member comprising a reinforced central portion and a non-reinforced end extending from the central portion so that said reinforced portion restricts said D-shaped plate member from bending when back pressure is applied to said plate, said plate twisting allowing the end of the plate to maintain or improve sealing contact with the valve seat.

Provided is a check valve comprising a valve body; a seat having an upstream side and a downstream side comprising an annular seat member, and a radial cross member; said annular seat member and said radial cross member defining a pair of substantially D-shaped bores; a radial hinge pin set parallel to said seat with said radial cross member on the downstream side.

A pair of substantially D-shaped plates, pivoted on said radial hinge pin and having an upstream side and a downstream side; said plates are rotatable between the valve open position and the valve closed position; said D-shaped plate members have a reinforced central portion and a non-reinforced end extending from the central portion; thus when back pressure is applied to said plates, said reinforced portion limits the bending of said D-shaped plate members and said plate deformation causes the end of said plates to maintain a sealing contact with said valve seat.

The preferred embodiment of the metal plate is cast or forged, the best solution being to manufacture it as a single part. The central part is preferably enhanced by locally increasing the thickness of the central part of the plate from a predetermined plate thickness, for example with the aid of a raised area on one or both sides of the plate.

The backflow leakage problem of the double-plate thin-plate check valve, which ensures that the sealing action is maintained and practically improved under the increased backpressure. Contrary to the prior art solution of making the seat and plate stiffer in an attempt to prevent them from distorting, the theory behind the research work of the present invention is that leakage is a characteristic of plate deformation even under small loads, and that designing the plate so that it can deform the end of the plate to maintain sealing contact with the valve body is achieved by combining the flexibility of the plate end with the rigidity of the central part of the plate.