The globe valves, unlike the gate valves, allow the fluid to be regulated or controlled at the same time that they isolate the line. They have a movable disk-type element and a stationary ring seat in a spherical body.
Their spherical body shape is divided in two halves, separated by an internal baffle. This has an opening that forms a seat onto a movable plug, also called disk, that can be screwed in to shut the valve.
Globe valves are used for applications that requires throttling and frequent operation. They are normally used as sampling valves, that are normally shut, except when liquid flows are taken, because since the baffle restricts flow, they are nor recommended where full, unobstructed flows are required.
Straight pattern globe valves are the most commonly used. They are also the ones with a smaller permissible pressure drop.
PARTS OF A STRAIGHT PATTERN GLOBE VALVE
Available both in cast and forged steel, it has been designed to meet all the requirements of ASME, API and British Standards.
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 connections, supplied on request.
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.
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 pieces clamping ring (193) and 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.
Constructed in stainless steel, machined from solid bar stock. The single piece non rotating stem is connected to the disc (8) by a rounded head connection trough bearing ring (31A), and a stem retainer (29) and disc nut (18) assure the integrity of the kit.
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 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, other materials can be supplied.
22-128 Gland bolts and nuts
The gland studs are of the eye-bolt type, which can be provided with live load systems, by means of belleville rings.
6 Seat ring
Supplied in forged stainless steel, hardfaced with Stellite-6 (2 mm of minimun thickness). Seat ring is renewable, normally welded to the body.
Sealing contact surface is lapped for a perfect tight seal. Contolled hardness differentials are maintained between the disc and the seat ring, as required by API 600 Std.
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 Hand wheel
The handwheel is normally supplied of Hammer type, made of cast construction.
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.
- 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 and inconel wire.
Gaskets can also be made in stainless steel.
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.
132 Spacer ring
Made of a single piece covering 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 pressure seal gasket and 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 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 pefect alignment of the unit.
193 Yoke clamp
The body-yoke connection is created by means of a bipartite clamping ring. The internal connection between the clamp, body and yoke is conical, assuring a perfect tightening.
Constructed in forged stainless steel.
Disc is of swivel type, allowed to turn round freely upon the stem. Normally is of loose, Plug type, though can also of Ball, Needle and Parabolic shapes (equal percentage). Contact face is overlayed with Stellite-6 (2 mm of minimun thickness).
The stem-disc combination can be adapted to Stop-Check function.
Other materials are available on request. The trim (•) components are:
- Seat ring seating surfaces
- Disc seating surfaces
- Disc nut
- Back seat seating surface
Source: Babcock Globe Valve