What is a dual plate check valve?
The dual plate check valve has two semicircular discs, and the inertia of each disc is less than half of that of the normal swing check valve. Because the rotating shaft has moved, the half disc can be thinner. It is required to achieve shorter linear motion of full opening. The two discs rotate around a single central hinge pin or a central rod.
Because this valve has a blockage in the center, it can not be cleaned or inspected by “pig”. This disadvantage must be considered, but this basic design concept is very suitable for large valves. A well-designed dual plate check valve has a high flow coefficient equal to or higher than the traditional swing design. Some manufacturers do not provide valves for pulsating flow. The installation of reciprocating machine and other positive displacement equipment shall be discussed with the valve manufacturer. Some turbines are prone to vibration when operating with certain system characteristics. In these cases, the possibility of vibration shall be evaluated.
The valve is installed vertically with hinge pins. When opened, the two discs rotate with each other, both pointing downstream. In order to prevent over travel, braking parts shall be provided.
Among these check valves, the wafer type is the most popular under all pressure levels, as shown in Figure.1. The clamp structure is quite economical and lighter than the flange valve. Higher pressures can be similar to lug type, with the outer diameter of the valve body the same as that of the flange. A set of studs can be used for clearance holes. In this design, the bolt is located outside the valve, but the size of the length of the “wafer type” structure is still maintained (api594 standard). Lug type (also known as wafer lug type) and double flange type are also popular in hydrocarbon industry. This type of valve is sometimes called dual plate check valve (API 594 standard). Double plate check valves can have three designs:
Traditional dual plate check valve
Non fixed dual plate check valve
Sleeve type dual plate check valve
Figure.1 Typical double disc wafer check valve
Traditionally, the hinge pin is configured to pass through the valve body and the pressure seal is provided by a threaded plug or flange. The non fixed design is to install all internals axially from one end of the valve body, and the internal stop fixes the chain pin without penetrating the valve body. The sleeve valve installs all internal components, including the valve seat, in a sleeve axially locked in the valve body. Similarly, the valve body does not have to be penetrated and there is a potential leakage path. Spare sleeves can be stored for quick repair in case of emergency. The sleeve can be repaired and inspected on the workbench rather than on site. All designs shall include a fixed spring baffle to enable each disc to spring open independently, balance and operate synchronously.
Usually. The valve has a cast steel body and sleeve and an 11/13Cr disc. The valve seat can be integral and hard faced or soft sealed. The valve diameter is DN50 ~ DN600, and the pressure can reach ANSI 150Lb – 1500Lb; If the valve diameter is less than DN300, the pressure can reach 2500lb. The diameter of the valve can reach DN2100 and the pressure grade of the valve can reach ANSI 4500lb at most. Some metal wafer check valves have a liner. PFA lined stainless steel valves are mass-produced with diameters of DN15 – DN100. The maximum pressure is 100bar and the temperature can reach 200℃. Cast iron wafer valve with aluminum bronze disc, diameter from DN50 to DN600; The pressure is 16Bar. The valve body can be protected from corrosion by epoxy resin.
Because these valves have two seals, the seals can respond to differences in flow rates. When the valve operates at unbalanced flow, the valve disc will open to different positions. Wear on a disc may be localized. If the valve discs bounce towards each other instead of stopping at a fixed position, operation damage and spring failure are likely to occur. The detailed valve design shall fully investigate the unbalanced flow distribution of the fluid (which may be caused by the elbow adjacent to the inlet).
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