double disc gate

Babcock valve’s double disc gate valve detail

DOUBLE DISC GATE VALVES

Double disc gate valves are a special design of gate valves that improves considerably the performance of the unit.

DOUBLE DISC WEDGE ASSEMBLY ADVANTAGES

Main advantages of double disc gate valves vs gate valves are:

RELIABLE OPERATION

upper wedge inclined face The Double Disc Gate Valve has been desig ned to assure reliable operation under the most severe service conditions. Due to the special configuration and geometry of the upper wedge inclined face, any possibility of locking the disc in closed position is eliminated, even when closed quickly or subjected to severe thermal transients.
LOW PRESSURE SEALING
tight seal throughout the entire range of operating differential pressures The wedge assembly is designed to impart sufficient thrust to each disc to maintain low pressure sealing. As the differential pressure across the disc increases, the seating load also increases, thus providing a tight seal throughout the entire range of operating differential pressures. Since the discs are independent of each other and the design is symmetrical, positive sealing can be maintained in either direction.
UNIFORM DISTRIBUTION OF SEALING PRESSURE
UNIFORM DISTRIBUTION OF SEALING PRESSURE   The tight seal is guaranteed even when the valve seats have become out of parallel due to body distortion, due to the uniform distribution of the sealing pressures allowed by the exclusive wedge design.
EASY MAINTENANCE
 EASY MAINTENANCE The four piece double disc wedge assembly can neither be incorrectly assembled nor become disengaged while in service. No special fitting at site is required for maintenance. The repair of minor seat or disc damage is greatly simplified because the seats and discs can be lapped inde- pendently of each other. Disassembly and maintenance can be accomplished without special tools or elaborate rigging.
UNIFORM SEAT WEAR
UNIFORM SEAT WEAR The incorporation of a unique revolving disc feature assures maximum seat life. The two independent discs, during each closing stroke and immediately prior to the disc seating, rotate a few degrees in the plane of the seats. This rotating action forces the disc to seat in a different position on each stroke, equalizing wear on the seats and the discs. This movement of the discs creates a lapping effect whenever the valve is operated, removing particles from the sealing surfaces before they can become wedged between the seats and the disc and cause damage.
RAPID CLOSURE
RAPID CLOSURE Babcock Valve’s Double Disc Wedge system permits rapid closure without seat distortion. Internal moving parts decelerate independently of each other with the result that inertial forces are dissipated in a series of impacts over a period of time. The largest of these is transmitted directly to the bottom of the valve body on a non-sealing surface. Forces transmitted directly to the seats are a small percentage of the total inertial forces. This is a distinct advantage over valve designs in which the total inertial force is absorbed directly by the seating surface 
PARTS 

Double disc gate valve1 Body

Available both in cast and forged steel, it has been designed to meet all the requirements of ASME, API and BS.

The body-bonnet connection is made by a pressure seal gasket. Its pre-stress condition is achieved by means of bolts screwed to the bonnet flange. Ends are normally butt-welding although they can be also flanged on request.

All bodies are provided with integrally cast bosses, located and sized in accordance with ASME B16.34, which allow the provision of drain and by- pass connections, supplied on request.

Four internal guides keep the discs assembly in place, ena- bling operation of the valve with stem in both vertical and horizontal positions.

Two internal bosses in the lower part of the body are machined to create the mechanical stop of the lower wedge.

2 Bonnet

Usually constructed in the same materials as the body, being designed so that the wall thickness always exceeds the requirement of API 600.

A back seat (13) bush is fitted inside the bonnet lower cavity, to provide a closure when de valve is fully open. This permits the valve to be repacked while in service.

The bonnet has a deep stuffing box in which packing rings are placed.

Stuffing box is designed with sufficient space to allow lantern ring to be fitted.

3 Yoke

Separate rigid yoke is provided to withstand the thrust of the actuator. Large windows allow easy access and ventilation of the packing area. The yoke is connected to the body by a two piece clamping ring (193) an four clamp bolts. This connection is very solid and enables easy maintenance at site.

The upper part of the yoke is suitably machined to house the yoke sleeve (11).

The yoke is usually made of cast carbon steel regardless the type of body material, unless otherwise required by the client.

4 Stem

Constructed in stainless steel, machined from solid bar stock. The simple piece stem in threaded in the upper wedge.

A conical shoulder is also provided to ensure effective and tight seal backseat which allows the stuffing box to be replaced with the valve in service. The stem dimensions conform to API 600. Special care is taken in the machining of the stem, including the final polishing of the travelling area (contact with the stuffing box). This allows a low- friction surface and a superior corrosion resistance.

5-125 Gland bushing and gland flange

They are supplied in two separate self aligning pieces, to ensure uniform pressure is effected during tightening of the packing.

The upper part of the gland, which comes in contact with the gland flange, is spherical in shape.

The gland flange is made of carbon steel but, upon request, materials can be supplied.

22-128 Gland bolts and nuts

The gland studs are of the eyebolt type, which can be swing outwards for ease of gland repacking.

6 Seat rings

They are supplied in forged stainless steel, hardfaced with Stellite-6 (2 mm of minimum thickness). Seat rings are renewable, normally welded to the body.

Sealing contact surfaces, are lapped for a perfect tight seal. Controlled hardness differentials are maintained between the wedge discs and the seat rings, as required by API 600 Std.

9 Discs

The two forged discs are made of the same material than the body, and the seating areas are hardfaced with 2 mm minimum thickness of Stellite-6.

The important benefits of these revolving discs are explained widely in another section of this catalogue.

11 Yoke sleeve

Designed to permit removal from the bonnet or yoke while the valve is in service.

The yoke bushing assembly is mounted in ball bearings. It is normally made of cast aluminium bronze, having high resistance to wear and high melting point. Other materials such as Ni-resist can be supplied on request.

13 Back seat

The back seat can be supplied as a threaded stainless steel bush, welded to the bonnet or of integral type. It can be hardfaced with Stellite-6 or orther materials as required.

This seat allows the valve to be repacked under pressure.

15 Handwheel

The handwheel can be supplied either in cast construction of fabricated from steel tube.

The handwheel is designed to allow easy operation of the valve. Other types of control are available and, in some cases, are indispensable for a good operation, for instance:

  • Chain wheel
  • Gear operator
  • Hammer handwheel
  • Geared hammer handwheel
  • Electric actuator
  • Electro-hydraulic actuator
  • Pneumatic actuator

17 Pressure seal gasket

The pressure seal gaskets are usually supplied of compressed graphite, bordered on the upper and lower edges with braided filaments of carbon fiber.

Gaskets can also be made in stainless steel.

68 Packing

Packing is made of an adequate number of preformed rings.

For general applicatios high grade graphite material is supplied, using compressed rings in the center and braided anti-extrusion rings on top and bottom. Graphite is selected of an approved quality.

Other types of packing are also available for particular services.

80 Disc retainer

The disc retainers are made of the same material than the body. They are firmly connected to the upper wedge and keep the discs in place while allowing their revolving feature.

The system of Stem, Discs, Upper Wedge and Disc retainers are crossed by a Wedge Pin (198) of Stainless Steel, connected by two nuts (129 A) and cotter pints (198 A).

132 Spacer ring

Made of a single piece coverting the upper part of the pressure seal gasket. It is normally manufactured in the same material as the body.

133 Gasket retainer

It is made normally of the same material as the body, and constructed in four pieces, called segments. The segments are sized to minimize the gap among them.

The segmental ring supports all the forces transmitted from the bonnet through the spacer ring. It is calculated to withstand all the force without cracking.

134 Bonnet retainer

Designed sufficiently resistant to withstand the forces transmitted by the bonnet screws (111).

The bonnet retainer is normally made of the same material as the body, but it can be constructed in any other material on request. It is machined to match exactly with the body, what guarantees a perfect alignment of the unit.

193 Yoke clamp

The connection between body and yoke is created by means of a bipartite clamping ring. The internal connection between the clamp, body and yoke is conical, assuring a perfect tightening.

7 & 7A Upper and lower wedges

The wedges ares constructed in forged or cast steel of the same material than the body. The contact surfaces are hardfaced with Stellite-6. The special geometry of these wedges has been designed so that they cannot became disengaged while they are sliding. The wedges impart thrust to the discs which move towards the seat rings (6) assuring a tight seal.

Two wedge springs (56) are located in the cavities between the upper and lower wedges, in order to absorb the inertial forces and permit a soft contact of the sliding inclined part of the wedges.

Double disc gate valves with pneumatic actuator

Double disc gate valves with pneumatic actuator

 STANDARD MATERIALS

Part
Denomination
Carbon
steel
Alloy
steel
Stainless
steel
1
BODY
ASTM
A 216 WCB
ASTM
A 217 WC9
ASTM
A 351 CF8M
2
BONNET
ASTM
A 105
ASTM
A 182 F22
ASTM
A 182 F316
3
YOKE
ASTM
A 216 WCB
ASTM
A 216 WCB
ASTM
A 216 WCB
4
STEM
ASTM
A 182 F6A
ASTM
A 182 F6A
ASTM
A 182 F316
5
GLAND
ASTM
A 182 F6A
ASTM
A 182 F6A
ASTM
A 182 F316
6
SEAT
RING
ASTM
A105+STELLITE
ASTM
A182F22+STELLITE
ASTM
A351CF8M+STELLITE
7
UPPER
WEDGE
ASTM
A216WCB+STELLITE
ASTM
A217WC9+STELLITE
ASTM
A351CF8M+STELLITE
7A
LOWER
WEDGE
ASTM
A216WCB+STELLITE
ASTM
A217WC9+STELLITE
ASTM
A351CF8M+STELLITE
9
DISC
ASTM
A105+STELLITE
ASTM
A182F22+STELLITE
ASTM
A351CF8M+STELLITE
11
YOKE
SLEEVE
ALUMINIUM-BRONZE
ALUMINIUM-BRONZE
ALUMINIUM-BRONZE
13
BACK
SEAT
ASTM
A105+STELLITE
ASTM
A182F22+STELLITE
ASTM
A182F316+STELLITE
15
HANDWHEEL
CARBON
STEEL
CARBON
STEEL
CARBON
STEEL
17
PRESSURE
SEAL GASKET
COMPRESSED & BRAIDED
GRAPHITE
COMPRESSED & BRAIDED
GRAPHITE
COMPRESSED & BRAIDED
GRAPHITE
20
SLEEVE
NUT
CARBON
STEEL
CARBON
STEEL
CARBON
STEEL
22
GLAND
NUT
ASTM
A 194 2H
ASTM
A 194 2H
ASTM
A 194 2H
24
YOKE
FLANGE
CARBON
STEEL
CARBON
STEEL
CARBON
STEEL
56
WEDGE
SPRING
AISI
302
AISI
302
AISI
302
68
INTERMEDIATE
PACKING
GRAPHITE
GRAPHITE
GRAPHITE
68A
END
PACKING
BRAIDED
GRAPHITE
BRAIDED
GRAPHITE
BRAIDED
GRAPHITE
75
BEARING
COMMERCIAL
COMMERCIAL
COMMERCIAL
80
DISC
RETAINER
ASTM
A515Gr70
ASTM
A182F6A
ASTM
A182 F316
87
SPRING
WASHER
AISI
304
AISI
304
AISI
304
111
YOKE
FLANGE CAP SCREW
AISI
4140
AISI
4140
AISI
4140
111A
BONNET
CAP SCREW
AISI
4140
AISI
4140
AISI
4140
118
GLAND
RETAINER CAP SCREW
AISI
4140
AISI
4140
AISI
4140
125
GLAND
FLANGE
ASTM
A 515 Gr 70
ASTM
A 515 Gr 70
ASTM
A 515 Gr 70
127
YOKE
CLAMP STUD
ASTM
A 193 B7
ASTM
A 193 B7
ASTM
A 193 B7
128
GLAND
BOLT
ASTM
A 193 B7
ASTM
A 193 B7
ASTM
A 193 B7
129
YOKE
CLAMP NUT
ASTM
A 194 2H
ASTM
A 194 2H
ASTM
A 194 2H
129A
DISC
RETAINER NUT
ASTM
A 194 2H
ASTM
A 194 2H
ASTM
A 194 2H
132
SPACER
RING
ASTM
A 105
ASTM
A 182 F22
ASTM
A 182 F316
133
GASKET
RETAINER
ASTM
A 105
ASTM
A 182 F22
ASTM
A 182 F316
134
BONNET
RETAINER
ASTM
A 515 Gr 70
ASTM
A 515 Gr 70
ASTM
A 515 Gr 70
193
YOKE
CLAMP
ASTM
A 515 Gr 70
ASTM
A 515 Gr 70
ASTM
A 515 Gr 70
194
GLAND
RETAINER
ASTM
A 515 Gr 70
ASTM
A 515 Gr 70
ASTM
A 515 Gr 70
195
GREASE
FITTING
COMMERCIAL
COMMERCIAL
COMMERCIAL
198
WEDGE
PIN
AISI
431
AISI
431
AISI
431
198A
COTTER
PIN
STAINLESS
STEEL
STAINLESS
STEEL
STAINLESS
STEEL

 

OTHER MATERIALS

Other materials are available on request. The trim components are:

  • Stem
  • Seat ring seating surfaces
  • Disc seating surfaces
  • Back seat seating surface

ASME CLASS

Asme class for valves

Notes

  • Ends to end dimensions are for short pattern, long patterns are available on request.
  • The valve weight is for Butt Welding ends.
  • Dimensions in mm. and weights in kg.
  • Dimensions not shown for classes 2500 and 4500 to customer requirements

 

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