5 replies to this topic

[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

[ankur2061]

irprocess,

Butterfly valves are used in gas service for control applications with pressure drop across control valves less than equal to 5 psi. Special valves are available for high pressure gas service. However, if you are looking for tight shut-off then it is advisable not to go for butterfly valves.

Have a look at the following link for more details:

http://www.weirpower...fly_valves.aspx

Hope this helps.

Regards,
Ankur.

[Qalander (Chem)]

Although our Ankur has given as usual the right advice; but here I just add my little bit in my way

"as we were told on process industry entry to Consider below 150 Psig as low pressure" your reference might indicate a similar concept,I assume!

[Homayun]

IProcess,

When the available pressure drop for your control valve is relatively low, you want to use a control valve that can have a good and reliable controlability with that low pressure drop. Usually a control valve is designed to consume ~ 20-30% of the frictional pressure drop. In your case you have something abour 0.4-0.5 Bar available for control which is quite low. That's why you need to a butterfly valve

[Zauberberg]

What do you want to control with this valve? Pressure (upstream or downstream)? Or flow through e.g. parallel loops? Please provide some basic process information.

Also, regarding your statement that butterfly valves are used in low pressure service, I believe this guideline refers to shut-off or ESD/isolation valves. Butterfly valves are known as valves not resistant to high torque which occurs when high pressure system is to be isolated from a low pressure system. This is a completely different subject from control valve applications. You can use globe valves in low DP application without any problems, but they are more costly, and bigger in size. Butterfly valves are the cheapest but once when installed they cannot be replaced with another type of control valve without significant piping modifications.

[sheiko]

My interpretation of the following quote from Perry's Handbook is that some types of butterfly valves can be considered tight shut-off (in low and high pressure service?):
"API 609 defines two major categories of butterfly valves: Category A and Category B. Category A valves are typically soft seated valves with shell pressure ratings that may be less than the flange rating of the valve. They are typically used for utility services and are commonly referred to as utility valves. Category B may be soft seated or metal seated, and must have shell pressure ratings equal to the full pressure rating of the valve flange, and seat ratings that essentially meet the shell rating within the temperature capability of the seat material. Within Category B, valves may be further divided into concentric shaft, double-offset shaft, and triple-offset shaft designs. Offset refers to the position of the shaft with respect to seat area. With minor exception, double- and triple-offset valve designs are metal-to metal seated. They are distinguished from other designs by their exceptional seat tightness (often "zero" leakage) that is maintained throughout the life of the valve. Their tightness exceeds the seat tightness capability and reliability of wedge-type gate valves".

Edited by sheiko, 11 November 2010 - 05:56 AM.