Design and Manufacture
Cast Steel Gate Valve to API 600 (ISO 10434) or API 6D
Cast Stainless Steel Gate Valve to API 603 or AP1600
Forged Steel Gate Valve to API 602.
Inspection and Test: API 598, API 600 or API 6D.
Pressure Temperature Ratings:ASME B16-34.
Face to Face and End to End:ASME B16.10.
Flange End Dimensions: ASME B16.5 (for NPS< 24): ASME B16.47
Series B,API 605 or ASME B16.47 Series A,MSS SP-44 (forNPS>24)
BW End Dimension:ASME B16.25.
Socket-Weld Dimension:ASME B16.11.
Design of Disc
Gate Valves with NPS > 2 are of wedge flexible gate:Gate valves: with NPS < 2 are of wedge solid gate.
Body and Bonnet Connection
The body and bonnet of Class 150 - Class 900 gate valves are usually connected with studs and nuts. And the body bonnet of Class 1500 - Class 2500 gate valves are usually of pressure seal design.
> 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 used 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.
Hand wheel or gear box is usually used for gate valve actuation. Chain wheel and electric actuator can be also used for gate valve actuation if being requested by the customers.
Belleville Spring Loaded Packing Impacting System
If being requested by the customer,the Belleville spring loadedpacking impacting system can be adopted for enhancing the durability and reliability of the paching seal.
Molded flexible graphite is used for packing material.PTFE or combined packing material can be also used if being requested by the customer. The internal surface of the stuffing box, of which area is connected with the packing, is of excellent finish (Ra3.2 m). 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 (Ra0.8 m) and ensure the reliable tightness of the stem area.
All our gate valves have the backseat design. In most cases the carbon steel gate valve is fitted with a renewable backseat. For stainless steel gate valve, the backseat is machined directly in the bonnet or is machined after welding. When the gate valve is at fully open position, the sealing of the backseat can be very reliable. However, as per the requirement of API 600, it is not advisable to add or change packing by the mean of backseat when the valve is Pressure containing.
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. Renewable threaded seat is used for NPS8 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 stainlees steel gate valve if being requested by the customer.
The stem is of integral forged design. The minimum 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 bigger than that of the T threaded part of the stem. The strength test of that area conforms to API591.
Usually, the stem nut is made of copper alloy it is also can be made of ASTM A439 D if being requested by the customer.For large sized gate valves (NPS10 for Class 150,NPSA 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 torque of the gate valve.
Special Gate Valve
Besides the common gate valves, nab also makes cryogenic gate valve,Jacketed Gate Valve,Extension Stem Gate Valve for underground application, Slat Gate Valve,etc.