Butterfly Valve

[irprocess]

In practice of TOTAL(Franch) company explained that butterfly valve is commonly used in low pressure gas lines,but not indicated which pressure is defined as low pressure.if everyone have any experience,pls share here.

also,I have a gas stream which the pressure in upstream and downstream of butterfly is 71.5 bara and 71.2 bara,please let me know this is applicable to use butterfly valve as control in system or no?

gas flowrate is 230 MMSCFD
temperature is 54.2 oC
and gas is H2S free
pipe size is 16 inch

Tanx

 

[JLSeagull]

The term low-pressure is not very specific but could apply to the top end of ASME Class 150.

The pressure rating generally declines as the line size increases. Triple offset butterfly valves rated ASME Class 600 are common up to NPS 12; some are available to NPS 16. Class 300 triple offset butterfly valves are available to NPS 36 (DN 900).

I think that triple offset butterfly valves can open and close with full ASME pressure class differential as a generalization. That would not be as likely for conventional butterfly valves.

 

[uu78hswang]

Butterfly valves may be used to control flow in pipes if
they are throttled in angles where the valve works stable
without noise or vibration or cavitation free.

So you may get the vlave cavitation coefficients compared
with reference s fot different valve sizes and use the maximum allowable pressure drop and flowrates through the valves to run without cavitation.

 

[jajam007]

We at our Ammonia Plant using butterfly valves as control valves on high pressure line i.e. 1800psig(124bar)at the inlet to Ammonia Converter and they are working well. But they are not good for perfect isolation especially at high pressure.

 

[dcasto]

In control service, the general rule of thumb is the control globe valve is 1 size smaller than the line. If you use a butterfly, its 2 sizes smaller, rule of thumb.

I use butterfly valves as the valve of choice for a by-pass around a filter. I won't use them where the pressure on each side exceeds about 150 psig. I won't use them where a leak could present issues.

 

[RODesigner]

In control valve selection is predominently depent on the type of control required. i.e. linear control or non linear control. Then comes the required isolations and operating parameters. Based on these type of control valve will be selected.

If you are looking for the fine control with great isolation; then globe valves are the choice. However these valves are expensive.

If the cost is main criteria for the selection then Butterfly valve is cheap and best.

POwer and Water Engg