Bellow Sealed Valves are a new breed of Industrial Process valves,designed to eliminate Valves leakage and are also known as ‘Zero Leak Valves’ or ‘Emission Free Valves.’
hese Valve , conventional gland packing is appended/supplemented by a metallic Bellow Cartidge joined to the valve bonnet at one end , and the stem at the other end . A bellow is a long accordion-like tube . As the valve stem strokes,the bellow expands or compresses with the stroke movement .There are no sliding or rotating through which process fluid can pass.
Thus the fluid will enter the valve from the seat of the valve &come in contact with the bellow, but will not come in contact with the stem. Since the stem is the only moving part in the valve, it is a source of potential leakage through the gland due to constant friction by the axial movement.
In a bellow sealed valve this potential leak is totally avoided due to the metallic bellow which blocks the leak path effectively by not allowing the media to come in contact with the stem and thus the gland.
A bellow is the heart of this type of valve.There are two types of bellows:
formed and welded leaf.A formed bellow is made by rolling a flat metal sheet into a tube with longitudinal fusion welding.This tube is then mechanically or hydraulically formed into bellows with rounded and widely spaced folds.
In Welded Leaf-Bellows,washer like plates of thin metal are welded together.Welding is carried out on both inner and outer circumference of the washer like plate .A welded leaf bellow has more folds per unit length in comparison with formed Bellows.
Thus, for the same stroke length ,mechanically formed Bellows are two to three times longer than their welded leaf counterparts. Reportedly mechanically formed bellows fail at random spots,while the welded leaf bellow usually fails at or near weld.
Why Bellow Sealed Valves?
Leakage from the valve gland is often a problem for the maintenance engineer. Losses incurred due to this type of leakage are considerable. Steam at 150 psi escapes through a gland with a clearance of 0.001 in. at a rate of 25 lb/hr. This means a loss of $1.2/8-hr shift and $1,100/yr. A tiny drop of 0.4 mm diameter/sec results in a waste of about 200 l/yr of costly oil or solvent.
Apart from this high cost of energy and material loss, the leakage also results in serious environmental, ecological and oftne hazardous problems. The leaking fluid can be corrosive, explosive or poisonous. Ina any case, it has to be checked before it leaks. A bellows seal valve can be a simple solution to all these problems.
Features Of Bellow Sealed Valves:
• Bellow Seal Valve comply with full condition at high temperature and high pressure.
• Bellow Seal prevents leakage of sensitive media which constitute high fire risk.
• Our bellows are capable of withstanding 8,000 cycles and above without failure under pressure.
• Steam at pressure of 150 p.s.i.escapes through a stem / gland clearance of 1 / 1000th of an inch at a rate of 24 lbs per hour.
