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A gate valve, also known as a sluice valve, is a valve that
opens by lifting a round or rectangular gate/wedge out of the path of the
fluid. The distinct feature of a gate valve is the sealing surfaces between the
gate and seats are planar. The gate faces can form a wedge shape or they can be
parallel. Typical gate valves should never be used for regulating flow, unless
they are specifically designed for that purpose. On opening the gate valve, the
flow path is enlarged in a highly nonlinear manner with respect to percent of
opening. This means that flow rate does not change evenly with stem travel.
Also, a partially open gate disk tends to vibrate from the fluid flow. Most of
the flow change occurs near shutoff with a relatively high fluid velocity
causing disk and seat wear and eventual leakage if used to regulate flow.
Typical gate valves are designed to be fully opened or closed. When fully open,
the typical gate valve has no obstruction in the flow path, resulting in very
low friction loss.
Disc Design
Solid and Flexible Wedge
Stem
Gate valves are characterized as having either a rising or a
non-rising stem. Rising stems provide a visual indication of valve position.
Non-rising stems are used where vertical space is limited or underground.
Bonnet
Bonnets provide a leak proof closure for the valve body.
Gate valves may have a screw-in, union, or bolted bonnet. Screw-in bonnets are
the simplest design, offering a durable, pressure-tight seal. Union bonnets are
suitable for applications requiring frequent inspection and cleaning. They also
give the body added strength. Bolted bonnets are used for larger valves and
higher pressure applications.
Another type of bonnet construction in a gate valve is a
pressure seal bonnet. This construction is adopted for valves for high pressure
service, typically in excess of 15 MPa (2250 psi). The unique feature about the
pressure seal bonnet is that the body bonnet joint seals improve as the
internal pressure in the valve increases, compared to other constructions where
the increase in internal pressure tends to create leaks in the body-bonnet
joint.
Body-Bonnet Gasket
Carbon steel or stainless steel + flexible graphite combined
gasket is used for Class150 gate valve; stainless steel + flexible graphite
spiral wound gasket for Class 300 gate valve; stainless steel + flexible
graphite spiral wound gasket for Class 600 gate valve, and ring type joint
gasket is optional for Class 600 gate valve; ring type joint gasket is used for
Class 900 gate valve; pressurized seal design is used for Class1500 to Class
2500 gate valve.
Operation
Hand wheel or gearbox operator are usually applied, if
required, chain wheel is available. Top flange dimension according to ISO 5211
is available for valves to be actuated.
Belleville Spring Loaded Packing
If required, Belleville spring loaded packing can be applied to enhance the durability, reduce fugitive emissions and increase reliability of the packing seal.
If required, Belleville spring loaded packing can be applied to enhance the durability, reduce fugitive emissions and increase reliability of the packing seal.
Packing Seal
Molded flexible graphite is normally used for packing
material. PTFE or combined packing material can be also adopted if required.
The internal surface of the stuffing box, of which area contacts the packing,
is fine finished (Ra 3.2μm). The stem surface, contacting the packing, should
be rolled and pressed after being precisely machined, so as to reach to high
finish and compactness (Ra 0.8μm) and to ensure the reliable tightness of the
stem area.
Back Seat
All GBA gate valves have a back seating design. In most
cases, the carbon steel gate valve is fitted with a renewable back seat while
for stainless steel gate valves, 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 is very reliable. However, according to API
600, the packing shall not be added or changed under line pressure.
Seat
For carbon steel gate valves, the seat material is usually
forged steel. The sealing surface of the seat is overlay welded with hard alloy
specified by the customer. Renewable threaded-in seat rings are used for
gate valves NPS≤10, and welded-on seat rings are optional and can be used
if required. Welded-on seats are used for carbon steel gate valves NPS
≤10. For Stainless steel gate valve, the seat is integral or hard alloy welded
integrally to the body. Threaded-in seat ring or welded-on seat is also
optional for stainless steel gate valves.
Stem
The stem is of one-piece wrought material, welding
fabricated is not permitted for FBV valves. The connection of the stem to the
disc is “T” type. The strength of the connecting area is higher than that of
the T threaded part of the stem. The strength test of the area conforms to API
591.
Stem Nut
Usually, the stem nut is made of copper alloy or ASTM A439
D2. 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), a roller bearing is fitted underside of
the stem nut in order to minimize the opening and closing torque of the gate
valve.
Cast Steel Gate Valve
Normative reference
API 600 Bolted Bonnet Steel Gate Valve for Petroleum
and Natural Gas Industries
BS 1414 Specification for Steel Wedge Gate Valves
(Flanged and Butt-welding Ends) for the Petroleum, Petrochemical and Allied
Industries
ASME B16.34 Valves Flanged, Threaded and Welding Ends
ASME B16.5 Pipe Flanges and Flanged Fittings: NPS 1/2
through 24
ASME B16.47 Series A Large Diameter Steel Flanges: NPS
26 Through NPS 60 Metric/Inch
Standard
ASME B16.25 Buttwelding Ends
ASME B16.10 Face to Face and End to End Dimensions of
Valves
MSS SP-25 Standard Marking System for Valves, Fittings,
Flanges and Unions
Size available
NPS 2 to NPS 36 (DN50 to DN900)
Pressure rating available
Class 150 to Class 2500
Standard Material Specification
Part Name
|
Material
|
||||||||||
Carbon Steel
|
Stainless Steel
|
||||||||||
Body
|
A216 WCB
|
A352 LCB
|
A217 WC1
|
A217 WC6
|
A217 WC9
|
A217 C5
|
A217 C12
|
A315 CF8
|
A351 CF8M
|
A351 CF3
|
A351 CF3M
|
Seat Ring
|
A105
|
A350 LF2
|
A182 F304
|
A182 F304
|
A182 F304
|
A182 F304
|
A182 F304
|
A182 F304
|
A182 F316
|
A182 F304L
|
A182 F316L
|
Wedge
|
A216 WCB
|
A352 LCB
|
A217 WC1
|
A217 WC6
|
A217 WC9
|
A217 C5
|
A217 C12
|
A351 CF8
|
A351 CF8M
|
A351 CF3
|
A351 CF3M
|
Stem
|
A182 F6
|
A182 F304
|
A182 F6
|
A182 F6
|
A182 F304
|
A182 F6
|
A182 F6
|
A182 F304
|
A182 F316
|
A182 F304L
|
A182 F316L
|
Bonnet Bolt
|
A193 B7
|
A320 L7
|
A193 B7
|
A193 B16
|
A193 B16
|
A193 B16
|
A193 B
|
A193 B7
|
A193 B7
|
A193 B7
|
A193 B7
|
Bonnet Nut
|
A194 2H
|
A194 4
|
A194 2H
|
A193 2H
|
A194 2H
|
A194 2H
|
A194 2H
|
A194 2H
|
A194 2H
|
A194 2H
|
A194 2H
|
Gasket
|
Stainless steel and graphite spiral wound
|
||||||||||
Bonnet
|
A216 WCB
|
A352 LCB
|
A217 WC1
|
A217 WC6
|
A217 WC9
|
A217 C5
|
A217 C12
|
A351 CF8
|
A351 CF8M
|
A351 CF3
|
A351 CF3M
|
Backseat Bushing
|
A182 F6
|
A182 F304
|
A182 F6
|
A182 F6
|
A182 F304
|
A182 F6
|
A182 F6
|
A182 F304
|
A182 F304
|
A182 F304L
|
A182 F316L
|
Stem Packing
|
Grafoil
|
||||||||||
Lantern Ring
|
A182 F6
|
A182 F6
|
A182 F6
|
A182 F6
|
A182 F304
|
A182 F6
|
A182 F6
|
A182 F304
|
A182 F304
|
A182 F304L
|
A182 F316L
|
Pin
|
Carbon steel
|
||||||||||
Gland
|
A182 F6
|
A182 F6
|
A182 F6
|
A182 F6
|
A182 F6
|
A182 F6
|
A182 F6
|
A351 CF8
|
A351 CF8M
|
A351 CF3
|
A351 CF3M
|
Gland Flange
|
A105
|
A350 LF2
|
A105
|
A105
|
A105
|
A105
|
A105
|
A351 CF8
|
A351 CF8M
|
A351 CF3
|
A351 CF3M
|
Gland Eyebolt
|
A193 B7
|
A320 L7
|
A193 B7
|
A193 B7
|
A193 B7
|
A193 B7
|
A193 B7
|
A193 B8
|
A193 B8
|
A193 B8
|
A193 B8
|
Gland Nut
|
A194 2H
|
A194 4
|
A194 2H
|
A194 2H
|
A194 2H
|
A194 2H
|
A194 2H
|
A194 8
|
A194 8
|
A194 8
|
A194 8
|
Stem Nut
|
C63000 or A439 D2
|
||||||||||
Retaining Nut
|
Carbon Steel
|
||||||||||
Handwheel
|
Ductile lron or Steel
|
||||||||||
H.W.Lock Nut
|
Carbon Steel
|
||||||||||
Yoke
|
A216 WCB
|
||||||||||
Nipple
|
Carbon steel
|
||||||||||