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| Standards Design and manufacture: Cast steel gate valve to API600(ISO10434) or API6D; Cast stainless steel gate valve to API603 or API600; Forged steel gate valve to API602. Inspection and test: API598,API600 or API6D. End flange dimension: ASME B 16.5( for NPS<=24; ASME B 16.47 series B, API605, ASME B 16.47 series A, MSS SP-44 for NPS>24) BW end dimension: ASME B 16.25 Socket-weld dimension: ASME B 16.11 Face to face and end to end: ASME B 16.10 Pressure-temperature ratings: ASME B 16.34 Gasket of cover flange Carbon steel or stainless steel+flexible graphite combined gasket is used for Class 150 gate valve; Stainless steel+flexible graphite wounded gasket is used for Class 300 gate valve; Stainless steel + flexible graphite wounded gasket is also optional for Class 600 gate valve; and ring joint gasket is also optional for Class 600 gate valve; Ring joint gasket is used for Class 900 gate valve; Pressurized seal design is used for Class 1500-2500 gate valve. Packing seal Molded flexible graphite is used for packing material. PTFE or combined packing material can also used if it's requested by the customer. The internal surface of the stuffing box, of which area is contacted with the packing, is of excellent finish(Ra3.2 um). The stem surface, contacting with the packing, should be rolled and pressed after being precisely machined, so as to reach to the high finish and compactness (Ra0.8um) and ensure the reliable tightness of the stem area. Body and bonnet connection The body and bonnet of Classs 150-900 gate valves are usually connected with studs and nuts. The body and bonnet of Class 1500-2500 gate valves are usually of pressurized seal design. Actuation Hand wheel or gear box is usually used for gate valve actuation. Chain wheel and electric actuator can also used if required. Belleville spring loaded packing impact system If being requested by customer, the belleville spring loaded packing impacting system can be adoptefor enhancing the durability and reliability of the packing seal. Design of disc Gate valves with NPS>=2" are of wedge flexible gate; NPS<2" are of wedge solid gate. Back seating design All our gate valves have the back seating deign. In most cases, the carbon steel gate valve is fitted with a separate back seat. For stainless steel gate valve, the back seat is machined directly in the bonnet or is machined after welding. When the gate valve is at fully open position, the sealing of the back seat can be very reliable. However, as per the requirement of API600, it is not advisable to add or change packing by the mean of back seating when the valve is ressure containing. Seat For carbon steel gate valve, the seat is usually forged steel. The sealing surface of the seat is spray welded with hard alloy specified by the customer. Separate thread seat is used for NPS<=10" gate valve, and welded on seat can be also optional if being requested. Welded on seat is used for NPS>=12" carbon steel gate valves. For stainless steel gate valve, integral seat is usually adopted, or to weld hard alloy directly integrally. Threaded or welded on seat is also optional for stainless steel gate valve is required by the customer. Stem design The stem is of intergral forged disign. The minimun diameter of the stem shall per the standard requirement. The connection of the stem and disc is T type. The strength of the connecting area is larger than of the T type threaded part of the stem. The strength test of the part area conform to API591. Stem nut Usually, the material of stem nut is ASTM A439 D2. It's also can be made of copper ally if required. For large size gate valve(NPS 10 for Class 150, NPS 8 for Class 300, NPS 6 for Class 600, NPS 5 for Class 900), rolling bearing is fitted at the two sides of the stem nut in order to minimize the open and close torgue of the gate valve. |
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