API St 594:2010 pdf free download.Check Valves: Flanged, Lug, Wafer, and Butt-welding
5.1.14 Type B valves shall have a bolted cover design that meets the requirements of ASME BPVC, Section VIII, flat covers shall conform to UG 34 and dished covers shall conform to Appendix I-6. Cover and cover flanges shall be circular except DN 50 and DN 65 (NPS 2 and NPS 2 1 / 2 ) may be of non-circular design. Body-to-cover joint shall be flanged with a flat face (Class 150 only), raised face, tongue and groove, spigot and recess, or ring joint per ASME B16.5.
5.1.15 The body-to-cover joint of Type valves shall have at least four through type bolts of the following minimum sizes:
3 / 8 in. when 50 DN 65 (2 NPS 2 1 / 2 );
1 / 2 in. when 80 DN 200 (3 NPS 8);
5 / 8 in. when 250 DN (10 NPS).
The total cross-sectional area of the bolts shall be in accordance with the requirements of ASME B16.34.
5.1.16 When valve design utilizes a stem that extends beyond the pressure boundary, stem retention shall be in accordance with Paragraph 6.5.1 of ASME B16.34. The design shall not rely on actuation components (e.g. gear operators, actuators, levers, etc.) to prevent ejection.
5.1.17 Type B swing check valves shall be equipped with single contact stop point, to prevent the possibility of disc getting stuck in the open position.
5.2 Plates and Disc
5.2.1 Valves are classified as follows.
A single-plate valve has a plate or disc that closes the valve when flow reversal or gravity forces the plate or disc against the valve-body seat. This closure may be aided by the use of springs or other devices.
A dual-plate valve has plates that close the valve with the assistance of one or more springs when flow reversal forces the plates against the valve-body seat. 5.2.2 For Type single-plate valves and Typevalves, when a nut is used to assemble the disc or plate to the hinge arm, the nut shall be positively secured to prevent separation of the connecting parts; the use of a single tack weld, lock washer or lock nut are not acceptable means. The closure assembly materials and design shall not limit the overall corrosion resistance of the valve.
5.2.3 The disc assembly design shall limit disc rotation to less than 360 degrees.
5.3 Seating Surfaces
5.3.1 The body and plate or disc seating surfaces may be of deposited weld metal, integral metal, mechanically retained metal, or a resilient material. On Type single-plate valves and Type valves, a resilient seal ring may be fitted either to the body or plate or disc seat as specified by the purchaser. The resilient seal ring shall be designed to give a full metal to metal seal if the resilient seal is inoperative or removed.
5.3.2 Welding is not permitted on cast iron or ductile iron.
5.3.3 Brazing is permitted on cast iron and ductile iron only for attaching seating surfaces to the body or the plate and only if agreed to by the purchaser and the manufacturer. Furnace brazing is the only type of brazing permitted and may be used only if the parts are heated under closely controlled conditions, in a uniform manner, and to a temperature no higher than the lower critical temperature of the base material. Cooling shall be in the furnace or in still air.
5.4 External Bolts and Threaded Holes
5.4.1 Bolts and threaded holes with a diameter 1 in. or smaller shall have coarse (UNC) threads. Those larger than 1 in. diameter shall be of the eight-thread series (8 UN). Bolt threads shall be Class 2A, and nut threads shall be Class 2B. Threads shall conform to ASME B1.1.
5.4.2 For bolts 1 in. diameter or smaller, threaded body-flange bolt holes shall be drilled and tapped according to the requirements for coarse thread series Class 2B in ASME B1.1. For bolts larger than 1 in. diameter, such holes shall be drilled and tapped according to the requirements for eight-thread series Class 2B in ASME B1.1.
5.4.3 For Type valves, cover flange bolts shall be continuously threaded stud bolts with heavy, semifinished hexagon nuts conforming to the requirements of ASME B18.2.2. Hex bolts or cap screws conforming to ASME B18.2.1 may also be used for DN 65 (NPS 2 1 / 2 ) and smaller valves. Hex bolts and cap screws shall be suitable for external wrenching only. 5.5 Flow Indication The valve body shall be furnished with a clearly visible cast, forged, machined-in, or die-stamped arrow to indicate the direction of flow through the valve.API St 594 pdf download.API St 594:2010 pdf free download
