6 replies to this topic

[Raj Mehta]

I have studied that diaphragm valves provide tight shutoff compared to butterfly valves. But in most large line cases we find butterfly valves and the reason highlighted is the cost factor.

Can someone compare between Butterfly & diaphragm valve in various aspects like cost, application areas, selection criteria, thumb rules, operating conditions etc. ?

Many Thanks,

Raj

[ankur2061]

Raj,

There is lot of information that you can collect from the internet related to butterfly and diaphragm valves and collate this information for a one-to-one comparison based on a wide range of parameters. One such link is provided below:

http://www.valvias.c...erfly-valve.php
http://www.valvias.c...hragm-valve.php

A very good link for valve type selection along with demonstrative videos is given at the following link:
https://controls.eng...eTypesSelection

Hope this helps.

Regards,
Ankur.

[kkala]

Butterfly valves were tried in phosphoric acid service of a fertiliser plant (~1979) and judged unsuitable due to leakages during shut off. These were due to gypsum contained in the acid, which caused a lot of deposits. On the contrary diaphragm valves, Saunders type, were satisfactory. Most suitable for the case was Saunders straight through valve (KB type).
We used butterfly valves on cylindrical air ducts (even dusty), since tight shutoff was not critical.
Indeed diaphragm valves of about 12" size could be hardly found in the market, bigger sizes (if existed) would have been even more rear (thus expensive).
However Saunders valves are not suitable for all types of slurries. For instance liquors in alumina industry create hard deposits, needing valves of Lunkenheimer type to "grind" them as they close (according to my information).
Above can give an idea on using these two kinds of valves for slurries. Butterfly seems to have drawbacks on slurry service. However valve application is quite specific, a (special) butterfly valve may have good references for a specific slurry. On the other hand Saunders valves have not been seen on clear liquid pipes.

Edited by kkala, 17 January 2013 - 05:31 PM.

[kkala]

Perry, Chapter of Transport and storage of fluids, Process plant piping contains a lot of information on valves (p. 10-87 to 10-91 in 7th edition), including Diaphragm and Butterfly valves.
Diaphragm valves are limited to pressures of about 3.5 barg (I remember a bit higher) and are excellent for fluids with suspended solids.
Butterfly valves occupy less space on the line than any other valve.
Note: Contrary to diaphragm, butterfly valves to control flow (manually) have been seen.

[breizh]

consider this resource .

Hope this helps

Breizh

[Art Montemayor]

Mehta28:

I don't believe that you can logically compare diaphragm valves with butterfly types for a specific service. I have, for many years applied both - but always in different services (which is the main reasor for their development and use).

For example, as Kkala points out, Saunders valves are reknown for having sucessful shutoff features when dealing with certain fluids containing solids. However, there are exceptions within this application due to particle size and other properties. One would never attempt to employ or even consider using butterfly valves in this application.

Similarly, employing a Saunders diaphragm valve in cooling water service is not only uneconomical, but a total "overkill". I doubt that anyone suggesting a diaphragm valve for cooling water service would be considered seriously.
Your basic query is devoid of practical aspects and is theoretical in concept. To my thinking, no one can compare between butterfly and diaphragm valves in cost, application, and operating conditions.

[Raj Mehta]

I thank everyone for providing their valuable inputs, sharing materials to read and giving me direction for further reading. Mr. Art: I now understand that every application is different and proper analysis needs to be done before selection. While theoretical knowledge is critical in deciding the options.