In particular chemical processes, the fluids in the pipes are often toxic, radioactive, and hazardous. Bellow sealed valves are used to prevent leakage of any toxic chemical into the atmosphere. The bellow can be supplied in different materials like 316Ti, 321, C276, or Alloy 625. Body material can be selected from all available materials.

Leakage at various points in pipelines found in chemical plants creates emissions. All such leakage points can be detected using various methods and instruments and should be noted by the plant engineer. Critical leakage points include flanged gasket joints and the Valve/pump gland packing, etc. Today the chemical process industry is gearing itself towards safer technology for better environmental protection and it has become every process engineer’s responsibility to design plants that limit damage to the environment through the prevention of leakage of any toxic chemicals.

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What is Bellow Seal Gate Valve?

A Bellow Seal Gate Valve is a specially designed valve suitable for use in industries dealing with a hazardous medium where even minute leakages can be extremely critical. With the exponential growth of new industries such as the chemical and nuclear industries, there is a growing abundance of flammable, hazardous, extremely poisonous, and toxic media flowing through the pipelines. This creates a high risk of leakage, explosion, and health hazards. So, the valves used in such pipes and systems have specific stringent leakage and sealing requirements.

Bellow Construction of Bellow Sealed Gate Valve

The bellow cartridge is welded to both the Valve Bonnet and the Valve stem. The bellow cartridge has a number of convolutions and these convolutions become compressed or expanded depending upon the movement of the Valve stem. (Scientifically speaking the bellow gets compressed when the Valve is in the open position and expanded when the Valve is in the closed condition). It is important to properly install the Valve bodies. The bellow can be sealed to the Valves in two different ways. Firstly, the bellow can be welded to the Valve stem at the top and the Valve body at the bottom. In this case, the process fluid is contained inside the bellow, or in the second method the bellow is welded to the Valve stem at the bottom and the body on the top. In this case, the process fluid is contained in the annular region between the Valve Bonnet and bellow (from the outside).

The bellow is a critical component and forms the heart of the bellow seal Valves. To avoid any twisting of the bellow the Valve must have a stem with linear movement only. This can be achieved using a so-called sleeve nut at the Yoke portion of the Valve Bonnet. A handwheel is fitted onto the sleeve-nut which effectively transfers a rotary motion of the handwheel into a linear motion in the Valve stem.

Bellow types of Bellow Seal Gate Valve

There are two main types of bellow.. the Forged Bellow and the Welded Bellow. Formed-type bellows are made by rolling a flat sheet (thin wall foil) into a tube which is then longitudinally fusion welded. This tube is subsequently mechanically or hydrostatically formed into a bellow with rounded and widely spaced folds. The welded leaf type bellow is made by welding washer-like plates of thin metal together at both the inner and outer circumference of the washers – like plates. A welded leaf bellow has more folds per unit length as compared to forged bellows. Thus, for the same stroke length, forged bellows are two to three times longer than their welded leaf counterparts.

Reportedly, mechanically forged bellows fail at random spots, while the welded leaf usually fails at or near a weld. To ensure full penetration of bellow ends and end coller welding it is advisable to fabricate using micro plasma welding.

Bellow Design of Bellows Seal Gate Valve

The multi-ply bellow design is preferred for handling higher-pressure fluids (generally two or three plies of the metal wall). A two-ply bellow can increase its pressure rating by 80% to 100% as compared to a single ply bellow of the same thickness. Alternatively, if a single ply bellow of a thickness equivalent to a pressure rating of a two-ply bellow is used, the stroke length is reduced. Thus, a multi-ply bellow design offers a distinct advantage over a single ply bellow. It is clear that the bellow is subject to metal fatigue and this fatigue can induce weld failure. The bellow fatigue life is affected by the material of construction, fabrication technique, stroke length, and stroke frequency, in addition to the usual parameters such as fluid temperature and pressure.

Specification of Bellow Seal Gate Valve

• Design standard: ASME B16.34
• Face to face dimension: ASME B16.10
• Flanged ends: ASME B16.5
• Test & inspection: API 598
• Nominal Size: NPS 1/2～16
• Pressure Rating: CL.150～CL.1500
• End Connection: RF/RTJ/BW/SW
• Body Material: Casting & Forging(Carbon Steel, SS, Duplex, Hastelloy)
• Trim Material: As per standard or order requirement
• Bellow Material：304/304L/316/316L/Inconel600/625/718

Features of Bellows Seal Gate Valve

• Long cycle life bellows (3000 cycles): Designed and qualification tested for high pressure/temperature service.
• Bellows monitoring port (optional): A plug can be connected to the space above the bellows to monitor performance.
• Two secondary stem seals: a) Backseat in an open position; b) Graphite packing.
• Superior seating faces: Seats CoCr alloy hardfaced and the wedge is solid CoCr alloy.
• Each valve is tested per API 598.
• Every bellow assembly is helium leak-tested to assure zero leakage.
• Non-rotating stems prevent torsion of bellow.
• Secondary stem seals include:
• Stem backseat
• API 624 stem packing
• Lubricant fittings to ensure proper lubrication of stem bushing for efficient opening and closing.
• Multiple bellows materials are available: 316Ti, Hastelloy, Inconel, Monel, etc.
• All bellows are hydroformed with a minimum of two layers.
• Available in pressure classes 150-1500 (All body materials available)

Applications of Bellow Sealed Gate Valve

The hot oil system, steam system, hot and cold water system, etc.