Double Plate Check Valve

Double plate check valves are automatic mechanical valves that open with forward flow and close with reverse flow. The main function of the check valve is to protect the mechanical devices in the piping system by preventing reverse flow of liquid. The check valve is a kind of low-cost check valve, but it has a greater impact effect. Dual plate check valves are more common in many industries than swing control valves because they have a low impact effect. Furthermore, the total cost of the double plate check valve, that is, purchase cost, operating cost and energy cost, is significantly lower than that of the check valve.

What is a dual plate check valve?

The dual plate check valve concept is the result of efforts to overcome the problems associated with the traditional check valve and lift check valve. The double plate check valve uses two spring loaded plates mounted on the center hinge screw. As the flow decreases, the movement of the torsion spring closes the plates before the flow reverses. This concept offers the dual benefits of “no water hammer” and “no knocking” at the same time. All the features together make the double plate check valve the most powerful and efficient design. It is also known as “SILENT CHECK VALVE”.

Classification of double plate check valves.

• According to body type.

1. Bracketless construction ensures that the valve body is not fully drilled to allow the hinge pin and stop pin to be installed in a dual plate check valve. Instead of drilling, a recess is milled.

The retainerless design with dual plate check valve also ensures greater integrity at high pressures, so there is little worry about body leaks.

• By type of end connection.

1. Trailer: Flanged contacts with terminals are similar to wafer contacts, but have slight differences. The eyelet holes are drilled and there is one eyelet hole for each screw hole in the flanges. And each threaded hole has two screws, one from each flange on opposite sides. This type of assembly can be used for dead-end operation, where there is a flange on only one side of the valve and the other is exposed to the environment, as long as the seat/support is well screwed.
2. Waffle: In wafer fixing, the valve is mounted between the pipe flanges and the pipe flange bolts are fixed to it. There are also some centering holes in the body of some wafer dies to ensure proper positioning of the valve between the flanges.

The wafer valve is the lightest housing variant for installation between pipe flanges. Therefore, the wafer valve is cheaper than other valves.

3. Table: The valve has a flange connection and screw holes that screw the flanges to the shaft. Flange brackets make removal and repair easy. Flange mounts are popular for larger size valves. Gaskets must be used where these flanges come together.
4. Butt welding: The ends of the valve and pipe are of similar diameter. The outer edge of both ends is machined to create a “valley” filled with weld metal. The two sections are welded at the edges as shown in the picture. Butt weld joints are typically intended for smaller diameters, typically 2 inches or less.

• By sealing method.

1. Soft Seal: Soft seal means that one of the seal pairs is made of low hardness materials. Generally, the soft seal seat is made of non-metallic materials with certain strength, hardness and high temperature tolerance to ensure no leakage. However, the service life and temperature adjustment are weaker than the metal seal valve. Although some suppliers argued that their hard seal valve could not produce leakage, the seal of the hard seal valve is still weaker than that of the soft seal valve. However, the corrosion resistance of the soft seal valve to a certain corrosive medium cannot meet the technical requirements.
2. Metal gasket: Both ends of the seal pair are made of metal or other metals with high hardness. The valve is therefore considered to be a rigid seal or metal-to-metal seal valve. Hard seal valves have low sealing force, but are resistant to high temperatures, corrosion and have better mechanical properties than soft seal valves, such as: B. Steel + steel, steel + copper, steel + graphite and steel + alloy steel. It can be cast iron, cast bronze, alloy steel, bead welding alloy or spray alloy.

How does a dual plate check valve work?

The valve plate opens when fluid pressure flows in one direction. If the fluid flows in the opposite direction due to fluid pressure and the impact of the plate on the valve seat, the flow will stop. The reduced flow would allow the torsion spring to close the plate without causing a reversal of fluid flow.

The valve has a cylindrical body and can have a much more linear voltage distribution compared to the configuration of other valves. The cylindrical body is designed to support excessive weight as well as valve weight or thickness. Therefore, this valve presents a clear advantage in terms of safety and economy under severe load conditions.

Features and Benefits of Dual Plate Check Valve.

Double plate check valve is a check valve that is comparatively stronger, lighter and more compact than traditional swing or lift control valve.

• Pressure loss with a double plate check valve is very low compared to other check valves.
• Minor wear on the seat as it has a no-knock design.
• Water hammers are almost insignificant on double plate check valves because valve closure does not depend on backpressure and backflow. Any plate half the size of a swing retainer plate provides a straight flow path and therefore lower resistance. Spring-assisted closing causes the valve to begin closing as soon as the flow rate drops below the minimum design speed, and then the flow flows into the flow reduction pattern. The valve closes when the flow rate reaches zero and well before the flow reverses. This reduces water hammer.
• Non-Impact Design: The two plates of the double plate check valve are mounted vertically in the center for horizontal installations, completely eliminating the influence of gravity. Furthermore, the thrust created when moving to the closed position is only a fraction of that created with a check valve. Furthermore, due to spring-assisted closing, the valve closes when the flow velocity reaches zero and until the flow reverses. As it begins to close, the flow cushions the panels and seat, reducing impact.

Application of double plate check valve.

A double plate check valve is the most suitable type of check valve that can be used for almost all material configurations and system parameters in various applications. Some of the typical applications are:

• Water systems such as boiler, drinking water, fire protection system, water cooling and heating system, etc.
• Petrochemicals: offshore/onshore applications, LPG, LNG, lubricating oil, cryogenics, etc.
• Hydrocarbons: In almost all applications.
• Air and gas applications such as chlorine, hydrogen, nitrogen, carbon dioxide, oxygen, etc.
• Metallurgical and chemical applications: sugar, pharmaceuticals, paper, cement, steel, aluminum, copper, zinc, etc.

Dual Plate Check Valve Installation Guide.

• Valve cleaning: The end connections of double plate check valves are fixed with anti-rust oil. Clean them before installation. Valve plates should be inspected to ensure they are free of rust/oil.
• Checking the flow direction: The flow direction in the line must correspond to the flow direction indicated by the “arrow” on the valve body and indicated on the nameplate.
• Horizontal piping: Insert the valve into the piping with the pin holders (caps) facing up and down.
• Installation clearance between check valve and butterfly valve: When installing the butterfly valve on the outlet side of the double plate check valve, make sure there is enough space between the two valves for the check valve plates to double plate are open. Furthermore, the butterfly valve disc must not touch the double plate check valve. Additionally, ensure adequate clearance to avoid peripheral or irregular flow conditions.
• The orientation of the valve in relation to the pump outlet: When connecting the double plate check valve to the pump, ensure that the pump flow follows both valve plates for best performance.
• As a rule, valves are configured to operate in an ideal open state when installed horizontally at a line flow rate of 2 to 2.7 m/s of water. The flow rate for vertical installation may be slightly higher than for horizontal installation. For liquids with a lower specific gravity, please specify this when making your inquiry.
• For cyclic flow applications, such as piston engine exhaust, contact the manufacturer.
• It is recommended that double plate check valves be installed where the flow velocity is uniform across the entire cross section.

Differences between double plate check valve and check valve.

• Double plate check valves are light in weight and therefore easy to handle whereas swing check valves are comparatively bulky and therefore more difficult to handle and transport.
• The structure of the double plate check valve is compact and well designed, while the check valve has a complex body shape, making it difficult to assess stress points in critical applications.
• The double plate check can be installed in both horizontal and vertical directions, while the swing check is suitable for horizontal applications.
• Due to the spring assisted closing, a double plate check valve can be installed for top to bottom flow. This is not possible with the check valve.
• Pressure drops and power losses are low with double plate check valves compared to swing check valves, regardless of pressure rating.
• A double plate check valve features an anti-slamming design, while a swinging check valve requires an external device to counteract the slamming effect.
• Compared to swing check valves, double plate check valves experience negligible water hammer.
• Due to shock loads and frictional wear, rocker valves require regular maintenance of the seat and hinges. Double plate valves, on the other hand, have a long service life and run smoothly.

Double plate check valves are also called zero speed valves. This concept offers everything that other conventional check valves lack. It is the most effective valve in use, regardless of the fluid and operating conditions, it is the easiest to handle and can be installed in any piping structure without restrictions.