Difference between ordinary globe valve and bellows seal valve
Ordinary globe valves are linear motion valves and are generally used to start, stop, and regulate the flow of fluid. The operation of these valves can either be done manually or automatically to regulates the flow of medium by moving a disk perpendicular to the seat. However, these valves are not suitable for use in industries dealing with a hazardous medium where even minute leakages can be extremely critical. With the growth of new industries such as the chemical and nuclear industry, 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, a specially designed valve suitable for use in such applications is developed and is known as bellows seal valve.
How are bellows seal valves different from ordinary globe valves?
- The basic difference is in the two valves is of the stem sealing. While ordinary valves use gland packing for stem seal, bellows valve uses metallic bellows as the sealing mechanism.
- When ordinary valves with gland packing are used in the system for heated oil transfers (permeability of heated oil is about 50 times that of steam), chances of hot oil spillage are quite high and can cause loss of equipment and property. In such cases, due to its construction, the bellows valve can ensure absolutely nil leakage. Metallic bellows are designed to last several thousand cycles.
- In ordinary valves, the shape of graphite packing cannot provide 100% effective sealing which is the main reason for frequent leakage of packing valve. As ordinary fillers are manufactured with graphite, if the purity of graphite is not adequate, its oil resistance would below. When heating oil being transferred is soaked in a graphite filler, certain graphite impurities get separated and flows along with it.
- The internal parts of the bellows valve are made of stainless steel, which can withstand a temperature of 425°C. Considering the life span of bellows seal valve, the duration of the general bellows valve is more than three years. Therefore, to maintain the reliability of output and to reduce the direct running costs, a bellow shut-off valve is preferred over ordinary seal valves in case of a system where heated oil is being transferred.
- The loss of flowing media is zero in the case of the bellows seal valve while the amount of leakage from the ordinary globe valve is considerably high.
- Ordinary valves are highly unsafe when the media is hazardous/poisonous but bellows valve can be used safely for almost any media.
- The initial cost of the bellows seal valve may be higher but the maintenance cost is very low. However, the initial cost of an ordinary valve may be low but when compared to the overall cost during its lifecycle it is quite high.
The unique design of bellows seal valve and its efficiency to provide leak-proof operations makes it the best-suited valve over ordinary globe valve for a wide range of applications, especially hazardous materials & where system media is at high temperatures.