Butterfly valves verses ball valves

Generally a Butterfly valves can open faster

Ball Valves have a bit more linear control of flow and less flow resistance

See previous discussion:

http://cr4.globalspec.com/thread/7118/Application-and-Advantages-of-Ball-valve-Diaphram-valve-Butterfly-valve

Butterfly valve dimension as per API 594 (Dual Plate Check Valve dimension) which will be less space and weight suitable to be use in Offshore Oil & Gas Platform compare to Ball Valve which is heavier and dimension as per ASME B16.10 similar to Gate, Globe & Swing Check Valve (2" and above). However, Butterfly Valve limititation is on Size & Pressure Class even for High Performance Butterfly Valve (Triple Offset) compare to Ball Valve.

'Advantages and disadvantages' is probably not an ideal description.

In simple terms:

Ball valves are generally used on smaller diameters of metal piping where screwing or welding are the means of assembling the piping system. They are suitable for higher pressures as may be found in these diameters. A butterfly valve is generally difficult to make below, say, 40mm diameter, whereas ball valves down to say 10mm diameter are as 'cheap as chips'.

As size increases and flanges begin to appear, the ball valve becomes expensive compared to the butterfly valve. Although large diameter ball valves are made, the butterfly uses far less material and is lighter than a ball valve or any given diameter, and will have a correspondingly lower value.

Butterfly valves associated with large diameter systems (e.g. municipal water supply where 600mm diameter is common) will have a relatively low pressure rating, which is related to the pressures to be found typically in these applications. A ball valve would probably not be justifiable in this situation because of its very high value.

Flanged butterfly valves can be a nuisance if the downstream piping is to be removed from the valve. Typically the valve is held between pipe flanges using the flange bolts, and removing the bolts also removes the closure; effective isolation will be required elsewhere.

However, for plastic piping systems, the ball valve may be found in diameters up to, say, 100mm, typically, as the change in pipe diameter causes little change in value for the valve.

Last weekend, our local fire department went round and tested some hydrants and spulled out the lines. They closed the ball valves rather quickly though with full mains pressure and the resulting hammer found 3 weak spots and caused major leaks!!

Boy were they popular with the water guys on saturday!!

They have been asked not to turn off the water so abruptly, but you know fire department folks!!! They know best!

Ball valves typically have a one of the smoothest interior fluid

flow profiles with minimum fluid turbulence [ fairly good

throttling characteristics]for

high pressure, high temperature,

[700 - 10000 PSI/700 - 7000 F ]

and corrosive chemical (severe

service) applications. The operating plug (the ball) is almost

always stainless steel that is mounted within a Teflon or Nylon

seat/disc.

The typical butterfly valve's main advantage is quick action in

shutting or opening flow of the fluid it services. The main

disadvantage is the butterfly disc is a major point of turbulence

once it is opened ( and subsequently does NOT function well as a

throttling valve because of this reason!! ... It is best to have a

butterfly valve fully shut or fully open.). The normal operating

pressure ranges of butterfly valves tend to be low to medium

pressures/temperatures (50 - 600 PSI )

try pigging a flutterby valve!!!!!!