Technical Requirements and Standardization of Check Valves per API 594
When supplying products marked with the API monogram, manufacturing must be carried out strictly by facilities holding a valid API license, in compliance with all regulatory requirements of Annex A. This standard establishes comprehensive requirements for design, material selection, dimensional characteristics, pressure and temperature ratings, and regulates acceptance testing protocols and supply procedures for the two main categories of check valves.
Category “A” check valves are characterized by a reduced face-to-face dimension as regulated by Table 2. Structurally, they can be designed as wafer, wafer-lug, or double-flanged. Double-flanged models (according to Table 3) are equipped with single or dual plates. Body materials include gray and ductile iron, carbon and alloy steels, nickel alloys, and other corrosion-resistant materials. The products are adapted for installation in piping systems with Class 125 and 250 flanges (ASME B16.1), Class 150 and 300 flanges (ASME B16.42), Class 150–2500 flanges (ASME B16.5), as well as flange connections per MSS SP-44 and ASME B16.47 (Series A).
Category “B” check valves are characterized by an increased face-to-face dimension (according to clause 5.1.2) and are designed for installation via flanged connection or butt-welding. The bodies of these valves are manufactured from steel, nickel-based alloys, and other high-strength materials. The end connections comply with ASME B16.5 (flanged) or ASME B16.25 (butt-welding) standards.
Operating Size Range
Type “A” Valves:
- Class 125 and 250: DN 50 – 1200 (NPS 2 – 48), excluding DN 90 (NPS 3 1/2);
- Class 150 and 300: DN 50 – 1200 (NPS 2 – 48);
- Class 600: DN 50 – 1050 (NPS 2 – 42);
- Class 900 and 1500: DN 50 – 600 (NPS 2 – 24);
- Class 2500: DN 50 – 300 (NPS 2 – 12).
Type “B” Valves:
- Class 150 – 1500: DN 50 – 600 (NPS 2 – 24);
- Class 2500: DN 50 – 300 (NPS 2 – 12).
Note: The use of DN 90 and DN 125 (NPS 3 1/2 and 5) sizes is not recommended due to their impracticality in modern piping systems.
Nominal Diameters
| DN | 50 | 65 | 80 | 100 | 150 | 200 | 250 | 300 | 350 | 400 | 450 | 500 | 600 | 750 | 900 | 1050 | 1200 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| NPS | 2 | 2 1/2 | 3 | 4 | 6 | 8 | 10 | 12 | 14 | 16 | 18 | 20 | 24 | 30 | 36 | 42 | 48 |
Technical requirements that must be specified by the customer when preparing the specification are provided in Annex B of the standard.
API 594 Specifications and Component Nomenclature
A typical nomenclature of valve assemblies and parts is presented in Annex C. Graphical materials (Figs. C.1–C.5) illustrate the design features of Type “A” and “B” valves. These images are for informational purposes and demonstrate the principles of component identification. EV Group China reminds that any valve design is recognized as compliant with the standard only if all technical parameters and tolerances established by API 594 are strictly met.