APCO CDD Double Door Wafer Check Valve

Compact non-slam check valve for refineries, process plants and HVAC

The APCO CDD double door check valve is made by DeZURIK to let flow pass in one direction and block it in the other. Spring-loaded split doors open when downstream flow builds the required pressure drop and are closed by spring torsion as the flow stops, so the shutoff is positive before reversal and surge and water hammer are minimized.

The bulletin recommends the valve for clean liquids and gases and says it has an excellent performance reputation in refineries, petrochemical and gas liquefaction plants, other process industries and HVAC. Its low weight and short laying length cut cost and installation effort against full-body swing check valves while keeping heavy-duty, continuous operation.

CDD technical specification

Design points from the bulletin

Shutoff is automatic and spring assisted near zero flow velocity. Lightweight split doors give a positive seal ahead of flow reversal and help limit slam and surge. The contoured body gives a short, straight flow path with little turbulence, and the very low cracking pressure of the spring-loaded doors reduces the energy needed to open the valve.

Resilient seats provide a bubble-tight seal that meets or exceeds API 598, and lapped metal seats also meet or exceed API 598. Carbon steel and stainless steel CDD valves meet ASME B16.10 and API 594 face-to-face dimensions and ASME B16.5 flange dimensions. Wafer valves from 2 to 6 in are dual rated for Class 150 and 300, while 8 in and larger wafer valves and all lugged valves are rated to Class 150.

Materials of construction

The ductile iron body keeps the anti-corrosive properties of cast iron while reaching a yield strength comparable to carbon steel and higher pressure-temperature ratings than cast iron. Carbon steel and stainless steel bodies are chosen for higher pressure or corrosion resistance. The bulletin also tabulates valve weights by size for ductile iron and for carbon or stainless steel bodies, which helps with handling and pipe support.

Selecting and installing a CDD

Order codes start with style CDD and size, then body material, door material and seat material; EPDM, NBR and FKM are the seat choices, with metal for the carbon steel body. Lifting eye bolts are supplied on 10 in and larger ductile iron valves and on 8 in and larger steel valves.

This is general practice: install a wafer double door check valve between flanges with the hinge pin horizontal when the manufacturer recommends it, keep straight pipe upstream, and avoid a velocity so low that the doors flutter. Check the line velocity against the 5 to 10 ft/s window in the bulletin, and review the flange gasket choice for the seat type.

Applications, related items and documents

As general engineering context, double door check valves protect pump discharges, compressor lines and header connections in Gulf refining, gas and HVAC chilled water systems, where weight and laying length matter. Confirm service fluid, temperature and flange rating against the table above.

See other check valves in Check Valves. The attached bulletin (10/2023) lists the weights per size and the materials of construction for ductile iron, lugged and wafer carbon or stainless bodies. Send size, body, door and seat when requesting a quotation from Seven Star LLC.

Using the CDD in Oman and the GCC

Double door wafer check valves are used in the region’s refineries, petrochemical plants, gas processing facilities, power stations and district cooling plants, where a short, light check valve fits between flanges in compact pipe racks. They are also used on cooling water, utility and HVAC lines in large buildings. The spring-assisted closure reduces slam and water hammer, which protects pumps and pipework.

For seawater cooling and desalination service, confirm the body, door, spring and seat materials against the water chemistry. Install the valve with enough straight pipe upstream, away from elbows and pump discharge turbulence, as recommended in the installation instructions, so the doors open fully and do not flutter. For gas service, check the minimum flow needed to keep the doors open.

Where the valve replaces an existing check valve, send its face-to-face length and flange data so the new valve fits the existing pipework.

Information to send with an enquiry

• Size, pressure class and flange standard
• Fluid, pressure, temperature and flow
• Body, door, spring and seat materials
• Any API or project specification
• Quantity