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 GRAND 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.