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●Standards
Design and Manufacture: Cast steel gate valve to API 600 (ISO 10434) or API 6D; Cast stainless steel gate valve to API 603 or API 600;
Forged steel gate valve to API 602.
Inspection and Test: API 598, API 600 or API 6D.
End flange dimension: ASME B16.5 (for NPS≤24)、ASME B16.47 series B、API 605 or ASME B16.47 series A、MSS SP-44 (for NPS＞24).
BW end dimension: ASME B16.25.
Socket-weld dimension: ASME B16.11.
Face to face and end to end: ASME B16.10.
Pressure-temperature ratings: ASME B16.34.
●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 and bonnet of
Class 1500～Class 2500 gate valves are usually of pressurized 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～Class 2500 gate valve.
●Actuation
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.
●Packing 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 contacted with the packing, is of excellent finish (Ra 3.2 μm). 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 (Ra 0.8 μm) and ensure the reliable tightness of the stem area.
●Belleville Spring Loaded Packing Impacting System
If being requested by the customer, the Belleville spring loaded packing impacting system can be adopted for enhancing the durability
and reliability of the packing seal.
●Back Seating Design
All our gate valves have the back seating design. In most cases, the carbon steel gate valve is fitted with a renewable 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 API 600, it is not
advisable to add or change packing by the mean of back seating when the valve is pressure 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. Renewable threaded seat is used for NPS≤10 gate valves, and welded on seat can be also optional if being
requested by the customer. Welded on seat is used for NPS≤10 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 if being requested by the customer.
●Stem Design
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 API 591.
●Stem Nut
Usually, the stem nut is made of ASTM A439 D2. It is also can be made of copper ally if being requested by the customer. For large
sized gate valves (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 torque of the gate valve.
●Special Gate Valve
Besides the common gate valves, Williamson Company also makes cryogenic gate valve, Jacketed Gate Valve, Bellow Sealed Gate
Valve, EXtension Stem Gate Valve for underground application, Flat Gate Valve, etc.
●Standards
Design and Manufacture: API 600 (ISO 10434) or API 6D
Inspection and Test: API 598, API 600 or API 6D
End flange dimension: ASME B16.5 (for NPS≤24)、ASME B16.47 series B、API 605 or ASME B16.47 series A、MSS SP-44 (for NPS＞24)
BW end dimension: ASME B16.25
Face to face and end to end: ASME B16.10
Pressure-temperature ratings: ASME B16.34
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