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Duo-Chek Parts

Duo Chek Parts Identification

Duo Chek Valves have Body Markings that will help identify the valve for the purpose of locating replacement parts. When replacing parts in dual plate designs, note the manufacturer of the wafer check valve and the valve Figure Number from the nameplate. If missing, look for other clues like pressure class markings (125, 150, 250, 300, 600) or body material markings: (Stainless Steels ASTM A351 CF8M, and Alloy 20 Stainless Steel A 351 CN7M, Duplex Stainless Steel, Hastelloy C-276 Stainless Steels, Carbon Steel A216 WCB, Low Temp Carbon Steel A352 LCB, or A352 LCC). If these features are known and the service media (for example wastewater pulp or gas production chemicals), and the face-to-face dimension are determined, the valve can be identified.

Duo Chek High-Performance Valves

Benefits dual plate designs offer when compared to swing check valves are leaking path prevention, efficient seating to prevent seat scrubbing, independent springs for balanced seating, overlaid metal seats in 410 stainless steel, or 316 stainless steel for hard-faced seating on metal-to-metal applications. Resilient seats offer seat scrubbing prevention not inherent in overlaid metal seats. High-performance designs incorporate pressure classes (150, 300, 600, 900, 1500, and 2500) with end connections in weld end (include bore schedule), ring joint (include flange class), and double-flanged (include flange class). 

What is a Duo-Chek Part? 

A Duo-Chek Part is a general-purpose or high-performance check Part, with a short face-to-face design. Unlike swing check Parts, the Duo-Chek Part is typically flangeless but is also made in a retainer less lug design, or double flanged retainer less design. Marlin is now owned by Crane Energy. The Marlin catalog is viewable at Authorized Parts, Inc. website. See:

Duo-Chek Part Types

Commonly known as dual disc check Parts, or Duo-Check Parts, dual plate designs have universal features common to Duo-Check Parts. They are spring-loaded and operate equally well in horizontal or vertical positions. Spring tension can be customized to accommodate low, minimum, standard, or high torque springs. Additionally, seating surfaces can be specified to meet service demands. Parts manufactured by Marlin Part Company, Houston, Texas conform to API 594, API 598, API 6D, API 6A, and ANSI B16.34 specifications.

True Duo Chek Wafer Check Valve Manufacturers

When identifying True Duo Chek Wafer Check valves, there are only a few names linked with this design of the valve. They include Stockham Valve Company, Marlin Valve Company, Mission Valve Company, Crane Valve Company, and TRW Mission. The size range is from 2” to 72” diameters.

Retainerless Duo-Chek

Beyond the basic style retainer less, there is lugged retainer less, double-flanged retainer less, and extended body. All styles of Duo-Check Parts are assembled with different material combinations, depending upon the service conditions. Body materials in Alloy 20, Cast Iron, Ductile Iron, WCB Cast Steel, 316 Stainless Steel, Bronze, Monel, Hastelloy C, WC6 Chrome-Moly alloy steel, Duplex stainless steel, and low-temperature LCB.  Seat material options are metal-to-metal seats, Buna-N, Viton, Teflon, Neoprene, EPDM, and Hypalon, for bubble-tight seating. Spring material options are Inconel 600, Inconel x-750, 316 stainless steel, or Monel. Request a material recommendation based on the service media. 

High-performance Part bodies are cast in finishes of a flat face, raised face, ring joint, or butt weld end in Pressure classes 125, 150, 175 UL/FM, 250, 300, 600, 900, 1500, and 2500 in pipe sizes 2” thru 88”. 

What is a Retainerless Duo-Chek Part Design? 

For critical applications, to prevent body penetration is the retainer less design, lugged retainer less, and double-flanged retainer less Duo-Check Parts that feature a one-piece body with no pin retainer penetration through the body. The internal design is the same as the basic Duo-Chek Part but offers no leak path due to the unique retainer-less feature. Special service Parts for hazardous or lethal service applications are most suitable for the retainer less design to prevent a possible leak through the Part body into the atmosphere. The design utilizes a one-piece body without pipe plugs, pin retainers, or outside bolting.

Typical applications to prevent body penetration of retainer less dual plate designs are Bleaching Lines, Black Liquor, Chemical Recovery, Chlorine Service, Aromatics, Acids, wastewater pulp, gas production chemicals, and Caustics. 

Duo-Chek Part Replacement Parts

Parts for Marlin Parts can be quoted if the Part size is specified, the figure number, and the serial number. Submit an RFQ with a list of parts that may include the Part Body, Plates, Stop Pins, Hinge Pin, Springs, Pin Insert, Snap Ring, Body Bearing, Plate Bearing, and Spring Bearing. 

Use Authorized Parts RFQ form at:

How to Order Duo-Check Parts

Duo-Check Parts employ a smart Figure Number System that allows for custom combinations of sizes and materials, or existing popular Figure Numbers. The first designation specifies Size, then Design Style, Pressure Class, Body & Plate material, Seat or Seal selection, Spring Alloy, and End Connection. 

For example: 18M300CSPSR = 18” Style M, Class 300, CS Body, SS Plates, SS Spring, Raised Face

See the figure number system at


Specify the Part size and figure number if possible. Include the serial number if available, then submit a list of parts: Part Body, Plates, Stop Pins, Hinge Pin, Springs, Pin Insert, Snap Ring, Body Bearing, Plate Bearing, and Spring Bearing can normally be supplied. Submit your RFQ on Authorized Parts website easy to use form at:

Yes, Duo Chek valves cross-reference to other manufacturer’s dual plate designs. However, not all design features are the same, so care should be taken when evaluating. There are a limited number of manufacturers associated with this design of valve. Stockham Valve, Gulf Valve Company, Marlin Valve Company, Mission Valve Company, Crane Valve Company, Goodwin Valve Company, Mueller Valve, Davis Valve, TRW Mission, Keckley, and Nibco. For fire protection systems please specify the valve as UL, FM or UL/FM.

Yes. All valve testing requirements can be made available for Wafer Check valves, including MTR’s, NDE, Pressure Testing, Radiography Testing, Magnetic Particle, Dye Penetrant, PMI, Positive Material Identification, Hardness Testing, and Failure Analysis.


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