Leakage from the valve gland is often a problem for the maintenance engineer.
Losses incurred due to this type of leakage are considerable. For e.g. (in a 15mm valve) Steam at a pressure of 150 psi escapes through a gland with a clearance of 0.001 in. at a rate of 25 lb/hr. This translates to a loss of approx $ 1.2/8-hr shift $1,100/yr.
A tiny drop of 0.4mm diameter/sec results in a waste of about 200 l/yr of costly oil or solvent. That translates to a loss of approx $1200/yr of a commonly used heating fluid like Dowtherm. And all this for $100 valve!!!
A part from this high cost of energy and material loss, the leakage also results in serious environmental, ecological and containment problems. The leaking fluid can be corrosive, inflammable, explosive or poisonous. In any case, a check needs to be kept on all leaks.
All bellow sealed valve can be a simple solution to all these problems.
Irrespective of proper selection, installation and periodic and preventive cares on conventional valves, leakages cannot be totally eliminated. Though performance seems to be satisfactory initially, they are bound to leak through gland after some operations. Selection of Bellow Sealed Valves is the only solution for this problem.
Therefore, use of bellow seal valve is on the increase.
Bellow Seal Valves because they Aid, help and complement-
- Stringent fugitive emission Laws
- Environment Protection Laws
- Air Purification or Clean Air Act.
- Greenhouse Effect Prevention Bill
- Energy conservation Law
Available in Gate / Globe / Angle valves versions. They incorporate a Metallic SS316Ti, Inconel 625, Hastelloy C276, etc which is flexible welded to the shaft at the lower end and to the Body-Bonnet Flange at the other thus effectively shutting off any leak/emission to the atmosphere.
TYPES OF BELLOWS
There are two main types of bellows viz “Welded Bellows” and “Formed Bellows”.
The following table will tell you just why :
|Type||Formed Bellow||Welded Bellows|
|Shape of Convolution||Sharp Edge||Round Edge|
|Durability||Reliable durability because bellows are produced from a single piece of metal. Guaranteed 10,000 cycles or more life cycle.||Of doubtful reliability because of a number of welded joints. Plies can be effected by Heat, and thus cycle life is hard to predict.|
|Suitability for use in valve||Because of wide opening between plies of bellows, bellow compression function will not be impaired by bits of foreign matter in fluid.||Wedge-shaped opening between plies will trap foreign matter in fluid, leading to bellow failure.|
|Quality Control||Easy to test for quality, bellow can be produced with uniform quality.||Very difficult to inspect welded spots for quality, hence quality difficult to control.|
The latter is made by a relatively newer technology in which a uniform bellow is produced from a thin tube. The shaping of the metal is carried out in a collapsible die under high fluid pressure.“SG ” prefers Formed Bellows From WITZENMANN hydra brand are imported from Germany incorporated in SG valves .