Bellow Seal Valve 2

[bmoorthy]

What are Bellow seal Valves. Under what circumstances this requirement is called for. Is this related to the sealing requirement near the Gland packing area or it an alternative to that. Are there any International standards which specifies design method for this bellow seal valves?

 

[jte]

bmoorthy-

Bellows seal valves are essentially valves which are less likely to have fugitive emissions problems by containing the valve stem mechanism in a bellows. Thus a valve stem packing leak will not leak to atmosphere. Due to the required flexibility of the bellows, the stems of these valves are LONG. They can be designed in for new construction, though that can be painful. Retrofitting into existing installations can be virtually impossible due to interferences.

Take a look at page 7 (in the .pdf, page 6 of the catalog)in

http://www.velan.com/products/pdfs/vel-bs-2001-web.pdf

for a good cutaway drawing of a bellows seal valve. A picture is worth a thousand words...

jt

 

[dancar]

In the High Purity Gas industry, bellows seal valves (sizes from 1/4' thru 2") are preferred in applications where long cycle life, metallic body sealing, ease of operation and low particulate generation are required. For instance, the average bellows valve design would have a cycle life of 10,000 cycles or more where a metal diaphragm valve would have a cycle life of aprox. 1000 cycles. However, in the smaller sizes the simplicity and strength of the springless packless valve (designed in 1982) would be preferred in applications where there is a limited cycle requirement. The pressure rating and purity levels are similar and the installation space and product cost are usually much less.

 

[NGiLuzzu]

Regarding the fugitive emissions, it must be observed that the German administrative regulation on air pollution called “Technische Anleitung zur Reinhaltung der Luft” (better known as TA-LUFT; latest edition: June 2002) takes "bellow sealing systems" as a reference: in fact, the acceptance criteria for all types of valves is to be "equivalent" to bellow sealing systems.
Such an equivalence is defined, in quantitative terms, by the German Engineers’ guideline VDI 2440 (November 2000) about emission control in oil refineries.

Hope this helps, 'NGL

 

[NGiLuzzu]

Please take also a look at Thread408-99985 about a related issue.

Thanks, 'NGL