What Bellow sealed Gate Valves?
Definition of Valve:Valves are mechanical devices specifically designed to direct, start, stop, or regulate the flow, pressure of a process fluid. Valves can be designed to handle either liquid or gas applications.By nature of their design, function, & application, valves come under wide variety of styles, sizes & pressure classes. Valves can be manufactured from different types of materials, like steel, alloys of steels, nickel alloys, iron or number of special alloys
Gate Valves: – A gate valve is a linear-motion valve that uses a typically flat closure element perpendicular to the direction of flow, which slides into the flow stream to provide shutoff. Overall, the simplicity of the gate valve design & its application to a large number of general, low-pressure drop services makes it one of the most common valves in use today. It can be applied to both liquid & gas services, although it is mostly used in liquid services. Gate valves do have some limitations. Gate valves do not handle throttling applications well because they provide inadequate control characteristics. Therefore, they are most commonly applied in simple on-off services as a block valve. The wedge shaped gate valve uses two inclined seats & inclined gate that allows for tight shutoff, even against high pressures. The inclined seats are designed 5 degree to 10 degree from the vertical plane.
Bellow Sealed Gate Valves: –The large volume & wide variety of hazardous & toxic materials in use, coupled with increasingly stringent regulatory requirements, makes positive containment & control mandatory. One of the serious valve problems is gland leakage resulting in waste & increased plant downtime. Apart from the high cost of energy losses, gland leakage can also cause serious environmental ecological & often health problems to the plant workers & personnel’s. Leakage of sensitive materials can constitute a fire hazard. There could be the risk of explosion, or corrosive materials could damage other equipments & also be harmful to the employees. Air entering the pipeline could produce inflammable explosive or poisonous mixtures.
- “Zero-stem” leakage eliminates product losses, hazards to humans, the environment & costly downtime ordinarily required for packing maintenance. SG brand gate valves with bellow seal construction eliminates the gland leakage absolutely & valve spindle is sealed with Stainless steel / Hastelloy-C 276 / Inconel-625 . Bellow either in single ply or multiply construction. Bellow with bottom bellow collar is welded to valve spindle at lower side & the top bellow collar at the upper side. This top bellow collar is held in between the body & bonnet joints or top bellow collar is directly welded to bonnet & glands are sealed to have Absolute Zero-Leakage. These metallic bellows can withstand
high pressure & temperature also. Body bonnet joints are with metallic gaskets to prevent the leakage or with welded type design.
Series of Valves
M/s SG Valves Pvt. Ltd produces wide range of Gate Valves. Classification of the Gate Valves will be done on the basis of,
- Types of valve:
- Gate Valves
- Bellow Seal Gate Valves
- Size & Class:
- ANSI / ASME CLASS 150,Sizes from ½” NB to 24”NB
- ANSI / ASME CLASS 300,Sizes from ½” NB to 24”NB
- ANSI / ASME CLASS 600,Sizes from ½” NB to 14”NB
- ANSI / ASME CLASS 800,Sizes from ½” NB to 2”NB
- ANSI / ASME CLASS 900,Sizes from ½” NB to 14”NB
- ANSI / ASME CLASS 1500,Sizes from ½” NB to 6”NB
- ANSI / ASME CLASS 2500,Sizes from ½” NB to 4”NB
- Type of construction:
- Casting valves
- Forging valves
- Fabricated valves
- Body –Bonnet connection:
- Bolted connection
- Welded connection
- Screwed connection
- End connections:
- Flanged end
- Butt weld end
- Socket weld end
- Screwed end
Bellow sealed Gate Valve:Gate valve is a linear motion valve in which the closure element is flat. The wedge slides up and down on the seating surfaces, found on both sides of the body. Gate valves are normally used for on-off service. Overall, the simplicity of the Gate valve design and its application to a large number of general, low-pressure drop services makes it one of the most common valves in use today. It can be applied both to liquid and gas services, although it is mostly used in liquid services. As an on-off block valve, it can be designed for full area flow to minimize the pressure drop and allow the passage of a pipe cleaning pig. When compared to other types of manual valves, the gate valve is relatively inexpensive as well as easy to maintain and disassemble
- Body:The design of the Body shall be such that it has to provide ample resistance to distortion under the maximum cold working pressure & under specified pressure at the maximum temperature. Body is the major pressure-retaining component of valve that houses the closure device, as well as inlet and outlet parts.
- Body End connection: The part of a valve that matches and joins with the matching piping.
- Bonnet: A pressure retaining part that house the packing box and guides, as well as seals the top works of a valve body. It has got a flange used to retain the Bonnet to the body or cylinder.
- Gate / Wedge: A flat and broad closure element that interrupts the flow stream. Gate shall be designed so that all parts can function properly independent of the installed valve orientation. Guide shall be provided in the wedge and shell, and shall be designed so as to minimize seat wear and maintain gate to stem alignment in all valve orientation. Gate to shell design shall consider wear that may be caused by corrosion, erosion and abrasion. Wedge gate shall be designed to account for seat wear.
- Seat Rings: It is hard or soft material. Used to seal a joint from the process fluid. They are used between the Body and Bonnet.
- Bellow: Bellow is a metallic component. It is flexible device that is welded to a stem or a shaft to provide a solid barrier between the process fluid and the atmosphere. The bellowsseal arrangement shall prevent leakage past the stem to atmosphere. The bellow shall have minimum of two plies.
- Bellow Collar: Bellow Collar is used as a supporting ring to weld the bellow to the stem. The bellow collar material is same as that of bellow material.
- Stem: The component attached to the closure device and the actuation device. Stem shall have a wedge attachment at one end and an external ACME thread form at the other end. The stem shall be one-piece material. Welded fabrication is not permitted.
- Back Seat:In linear valves, a special design that permits a portion of the stem to seat against the bottom of the bonnet to help prevent process flow from migrating into the packing box.
- Gland Bush: A part found at the top of the packing box that protects the packing Box from atmospheric elements and transfers force from the gland flange bolting to the packing.
- Gland Flange: Valve part used to retain & compress, packing by applying Bolting Load.
- Packings: A soft material used to prevent the leakage of process fluid from around a valve stem or shaft and the bore of the Bonnet.
- Yoke Sleeve: In Globe/Gate Valves, the part that provides a sliding seal surface for a pressure balanced plug.
- Eye Bolt / Nut: Eye Bolt / Nut is used to connect the Gland Flange to the Bonnet. By tightening the eye bolt nut proper sealing of the packing can be done through the Gland Bush
- Hand Wheel: A manual operator with a wheel that turns clockwise or counter clockwise to manually operate the valve. Normally clockwise to close the valve.
- Hand wheel Nut: Hand wheel nut is fitted to the yoke sleeve. Outer portion of the threading that prevents the movement of Hand wheel coming out from the yoke sleeve.
- Yoke Nut: Yoke nut fitted the top of bonnet, which resists the upward movement of the yoke sleeve due to upward force creating due linear motion of the stem.
- Top Bellow Collar (TBC):TBC is the supporting ring for the Bellow to weld at top side. It is placed in between the body and the bonnet /cylinder. The material is same as that of bellow material. In some cases the TBC is directly welded to the Bonnet.
- Cylinder: Cylinder is a connection between the bonnet and body in case of Bellow Seal Gate Valve. The Bottom flange of the cylinder is fitted to the body top flange with the help of studs and nuts or by welded construction. Cylinder may be made from sand casting or fabricated one, and cylinder is also known as extended bonnet.
- Stud/Fasteners: A threaded rod in which both ends are secured with a nut. Used to connect various joints of valves such as Body, Bonnet, Cylinder, Side Flanges etc.
- Gasket: A Gasket produced with simple inside & outside diameters with even, flat surfaces. A gasket consisting of alternate layer of metallic & non-metallic materials would together.
- Hand Wheel Key: Hand Wheel Key is used to transfer the rotary motion of the hand wheel to yoke sleeve, which in turn moves the stem linearly
- Screw/washer: Holds the eye bolt firmly with the Bonnet. It is placed at the bonnet rib provided
- Grub Screw: Grub Screw is fitted at the Top Flange of the Bonnet to prevent rotation of the yoke nut.
- Grease Nipple: Grease Nipple is fitted at the Top Flange of the Bonnet where the Yoke Sleeve seats. With the help of Grease Nipple we can provide proper lubrication to the rotating Yoke Sleeve, which in turn reduces the friction between the mating parts.
Bellow sealed Gate Valve Operation: In the full open position, as flow enters into the inlet of the valve and passes out through the outlet, there is no pressure drop. Any pressure drop that occurs is due to the geometry of the seats, body guides or cavities. When the wedge is in open position, the flow opening of the gate is exposed to the full flow
When the valve begins to close, the wedge begins its downward travel into the flow stream. Since gate valves operate in low pressure or low-pressure drop applications; the introduction of the gate into the flow stream is met with only moderate resistance.
As gate valve closes wedge begins to seal the flow as the upstream pressure builds. In the gate design the upstream pressure acts upon the floating seat, pushing the seat against the seating surface of the gate providing the necessary seal. In the wedge gate design, when the wedge reaches the seat, thrust applied by the manual operator pushes the gate into the seat. As additional thrust is applied, the wedge gate is pushed harder into the seats, providing tighter shut-off.
While the parallel valve requires minimum thrust to close upon opening, it must overcome a greater breakout force because of the upstream pressure pushing against the floating seat, especially if the valve has been in the closed position for some time. Once the flow begins to move through the seat and velocity builds, the upstream pressure is reduced and the gate slides easily to the full open position without much resistance from the flow