Bellows Sealed Valve

In this article, the author Mr. Satish Chidrawar (at the bottom of this page you will find more about the author) first reviews the construction, design and operation of the bellow seal. He then provides various examples of where bellow seal Valves are use.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.

 

We are an ISO 9001:2008,ISO 9001-2008, ISO 14001-2004, OHSAS 18001-2007, NSIC-CRISIL, EEPC, and QA-UKAS (ISO 9001-2008), SSI Certified company that follows total Quality Management System. and have been recognized as one of the world’s leading stockists and manufacturer of quality metals for over two decades and are committed to quick responses, unsurpassed quality, competitive pricing, reliable deliveries and an exhaustive inventory.Globe Valves are extensively employed to control flow. The range of flow control, pressure drop, and duty must be considered in the design of the valve to avert premature failure and to assure satisfactory service. Valves subjected to high-differential pressure-throttling service require specially designed valve trim.Generally the maximum differential pressure across the valve disc should not exceed 20 percent of the maximum upstream pressure or 200 psi (1380 kPa), whichever is less. Valves with special trim may be designed for applications exceeding these differential pressure limits.

Globe valve Specification

Type	Globe Valve
Standred	DIN 3352 F5
Material	Industrial-grade steel, carbon steel, stainless steel, alloy steel and special steel, A105, A182, F304, F316
Size	1/2"-2"
Diameter	1”to13”
Order	Accept custom order

 

Bellow types

Plug valves are available in a nonlubricated or lubricated design and with several styles of port openings. The port in the tapered plug is generally rectangular, but they are also available with round ports and diamond ports.Plug valves are also available with cylindrical plugs. The cylindrical plugs ensure greater port openings equal to or larger than the pipe flow area.Lubricated Plug valves are provided with a cavity in the middle along there axis. This cavity is closed at the bottom and fitted with a sealant-injection fitting at the top. The sealant is injected into the cavity, and a Check Valve below the injection fitting prevents the sealant from flowing in the reverse direction. The lubricant in effect becomes a structural part of the Valve, as it provides aflexible and renewable seat.

Nonlubricated Plug valves contain an elastomeric body liner or a sleeve, which is installed in the body cavity. The tapered and polished plug acts like a wedge and presses the sleeve against the body. Thus, the nonmetallic sleeve reduces the friction between the plug and the body.

 

Bellow design

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.

Bellow materials

The most popular stainless steel bellow material is AISI 316Ti which contain Titanium to withstand high temperatures. Alternatively, Inconel 600 or Inconel 625 improve fatigue strength and corrosion resistance as compared with stainless steel bellows. Similarly, Hastalloy C-276 offers greater corrosion resistance and fatigue strength than Inconel 625. Fatigue resistance can be improved by using a multiply bellows system and reducing the stroke length; this can significantly increase the bellow service life.

Valve options

The most common Valve types to be fitted with bellow seals are the gate and globe designs (see Figure 1).These are very suited for use with bellows due to their internal construction and axial movement of the Valve stem.
Based on available information, it seems that current bellow seal Valves range in size from 3 mm NB to 650 mm NB. Pressure ratings are available in from ANSI 150# to 2500#. Material options for the Valves include carbon steel, stainless steel and exotic alloys.

Applications

• Heat Transfer media: hot oil is commonly used in industries such as synthetic fibres / POY (Partially Oriented Yarn). However, there is always a risk of fire due to hot oil spillage on highly inflammable chemicals. Here, bellow seal Valves can stop the leakage.
• Vacuum / ultra high vacuum: some applications require a vacuum pump to continually extract air from a pipeline. Any conventional Valves installed on the pipeline can allow external air to enter the pipeline thorough the Valve stuffing box. Hence the bellow seal Valve is the only solution to prevent air from passing through the stuffing box.
• Highly hazardous fluids: for media such as chlorine, hydrogen, ammonia and phosgene, the bellow seal Valve is an ideal design as leakage through the gland is totally eliminated.
• Nuclear plant, heavy water plant: in instances where radiation leakage is to be prevented at all times, the bellow seal Valve is the ultimate choice.
• Costly fluids: in some applications leaks need to be avoided simply because of the high cost of the fluid. Here, an economic assessment often favours the use of bellow seal Valves.
• Environmental standards: around the world, standards regarding emissions and the environment are getting more stringent day by day. It can therefore be difficult for companies to expand within existing premises. With the use of bellow seal Valves, expansion without additional environmental