Butterfly valves, as you may already know, are a type of quarter-turn valve with disc-shaped seatings. The disc sits perpendicular to flow of when the valve is closed and parallel to flow when the valve is open. These valves are handle-operated, gear-operated, or mechanically/pneumatically actuated. While the operation of butterfly valves is straightforward, most people do not know about the different types of butterfly valves that exist.
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With butterfly valve options such as different body types, materials, and operation methods, many types of butterfly valves are available. First, let's examine the different body types, then move on to materials and operation methods. These factors tell you what the valve is capable of. Choosing butterfly valves for your application can be difficult, so we will attempt to make it easier with this blog post!
Butterfly Valve Body Types
Butterfly valves are popular because of their low-profile designs. They are thin, usually taking up much less space in a pipeline than ball valves. The difference in the two main variations of butterfly valves is how they attach to the pipeline. These body styles are lug and wafer style. What's the difference between lug and wafer style butterfly valves? Keep reading to find out.
Lug style butterfly valves (shown below) act much like a true union ball valve. They allow either of the adjacent pieces of piping to be removed while the system is still in operation. These valves do this by using two different sets of bolts, one attaching to each of the adjacent flanges. The remaining set of bolts keeps a strong seal between the valve and one piece of piping. Lug butterfly valves are perfect for applications where cleaning and other maintenance needs to be done regularly.
Wafer style butterfly valves (shown below) do not have the multitude of bolt mounts that make lug BF valves obvious. They usually have just two or four holes to secure and align the valve with the pipeline. They sit very securely, typically giving them twice the pressure rating of comparable lug-style valves. The major downside of wafer butterfly valves is that they do not allow easy maintenance like lug valves. Any maintenance in or around a wafer style butterfly valve requires a system shutdown.
Each of these butterfly valve choices has its own strengths, so choosing one depends on what you need it to do for you! We have looked at the different body types available, but what are our material options?
Butterfly Valve Materials
Like other types of valves, butterfly valves come in a wide range of materials. From stainless steel to PVC, the choices are basically limitless. A few materials are especially popular though, so let's take a look at them!
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PVC is one of the most common plastics for butterfly valves. A few qualities make them ideal for many moderate-to-low intensity applications. First, they are lightweight while still possessing impressive structural integrity. Second, they have wider ranges chemical compatibility than most metals. Finally, PVC and CPVC are both inexpensive compared to their metal counterparts. Check out our wide range of PVC butterfly valves or CPVC butterfly valves by clicking the links!
Cast iron is a go-to metal for butterfly valves. Cast iron has considerably more structural integrity and temperature range than PVC or CPVC, which makes it a great option for industrial processes that require something tougher. Among metals, iron is the inexpensive option, but this does not make it ineffective. Cast iron butterfly valves are versatile, which makes them perfect for a wide range of applications. Our parent company Commercial Industrial Supply carries butterfly valves for industrial applications.
How to Operate Different Types of Butterfly Valves
Method of operation also distinguishes butterfly valves from each other. The two manual methods are handles and gear wheels. Automated actuation is also possible, depending on the model! Lever-operated butterfly valves use a quarter-turn lever, often with a locking mechanism, to turn the valve's stem, thus opening and closing it. This is the simplest form of BF valve operation, but it is impractical and difficult for larger valves.
Gear wheel operation is another common method for opening/closing butterfly valves! A hand-operated wheel rotates a gear, attached to the stem, to move the disc. This method is used for all different types of butterfly valves, both big and small. By using a mechanically intuitive method to turn the disc instead of just human strength, gear wheels make butterfly valve operation even easier.
The final method of butterfly valve operation, typically reserved for high demand industrial applications, is actuation. This is automated opening and closing, which is necessary with large butterfly valves. Actuators only fit on specially-made valves that meet certain mounting standards. That is a different blog post, so we won't attempt to cover those standards here.
You now know everything you need to know about the different types of butterfly valves! They are extremely useful for all kinds of applications, so it makes sense that so many different varieties exist.
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I apologize if this topic has been discussed before. I could not find it using the search tool. I work for a water supplier and I am responcible for writing specs. We have repeatedly argued over what valve is superior in a distribution system and a transmission system. Our system is over 100 years old. We have pressures ranging from 40-PSI to 150-PSI. We originally installed double disc gate valves with integral bypass valves. We are seeing failures of some of these valves and are writing specs to replace them. Should we go with butterfly valves? What are the pros and cons to each? We are also considering resilient wedge gate valves, but some are questioning the life expectancy of the rubber. Is that an issue?
Thanks in advance for any help!!!
That is a good point penpiper, but it is deeper than that. Valves made in the 19th century were not built to a standard flange-to-flange dimension, and virtually any modern valve that you buy will require piping modification--adding a 1-inch pup is pretty similar to adding a 6-inch pup.
My experience with gate valves (both as an operator and a designer) is that they are quite tedious to operate. A quarter turn valve is a lot less tedius (even with a gear operator). You've limited your universe to gate valves and butterfly valves. Some reason you've excluded ball valves? If long-term maintenance is a driving characteristic I would bet that ball valves would give you superior performance for about the same money as gate valves.
I'm not a fan of butterfly valves in most applications. My experience with them has been that the resilliant seat doesn't last decades, and that for high-velocity flows, the von Karmen streets downstream of the open flapper can represent a lot of force on the rod holding the flapper in place. A lot of people use them "successfully" (whatever their individual definition of "success" is), I just never have.
David
Biggest con I see with butterfly valves vs gate valves is that you have the disc sitting in the stream with butterfly valves which means less flow and wear on the disc. I would imagine that the maintenance on them is much greater.
the pros is that they are lighter weight and only quarter turn so they operate faster and since they are usually soft seated they have a better shutoff vs metal seated gate valves.
I think it depends on the size when talking ball valves. On smaller sizes I think the extra cost of the ball might be worth the switch But large diameter ball valves are quite expensive and I'm not sure the switch from gate valves is worth the extra cost.
You didn't really say but it appears that the gate valves in your system lasted quite a long time so another fact to consider is it worth changing the system parameters for something you know worked for decades?
Thanks so far!!!
I think a little clarification is needed. Valves were mostly direct bury with either bell by bell or spigot ends with poured lead joints. Replacing those we would cut the cast iron pipe on each side and replace with mechanical joints. Small spool pieces of ductile iron would be inserted into the mechanical joints and couplings would secure the new valve to the old cast iron. In addition, some type of clamp, such as the steel restraint clamps supplied by Ford, and 1-inch threaded rods all wrapped with wax paper for restraint.
Valves in vaults may have been flange by flange, so the above about spacing and cost could be correct.
We still have the ongoing disagreement over which valve is superior or more correctly which valve should be used when and for what reasons.
Here are some of the arguments I have to address:
butterfly valves are easier to operate, they cost less, they do not seal tightly, they can be throttled, the seats could be damaged during throttling
gate valves are hard to operate, they cost more, they are designed to seal tightly, they can not be throttled,
the rubber used for resilient wedge gate valve and/or the resilient seat on butterfly valves may not have a design life of 100 years and may be as little as 30years
Should I be considering going back to a metal seated double disc design???
I see you fail to mention the common diameters of the valve, and also your country. By watermains in Europ with longlife requirement, it is most common to use double eccentric butterfly valves, but not!from high-quality producers.
Mains in this case would be pipelines for pressure class PN10, PN16 and PN25 (bars) and dimensions from about DN150/DN200 or somewhat higher, for instance from DN250
See for instance (several others)
Note: with lifetime IP68 gear.
With gear placed correctly (when ordered), valve stem will remain horizontal with gear-operaator spindle up.
For theese types of double eccentric butterfly valves the quality of valve, gear, sealing construction and general flow charecteristic, way of operation and lifetime expectancy will be far above centric butterfly valves, and much cheaper than ballvalves.
The seat sealing construction (seals with integrated sealrings secured adjustable and mounted on the disc) will not be ripped out by waterhammer for this type of valve.
Valves might be throtteled for smaller delta Ps with slightly better charecteristics than a common centric valve, and somewhat increased range, but will of course cavitate by throtteling at higher delta Ps' as centric valves.
The geometrical and seal construction will give thight lifetime sealing.
For 100 years lifetime for theese dimensions the double eccentric ballvalve (sample: same factory) could also be considered.
For smaller valves in the street distribution net: different type of gatevalves or ballvalves.
You need to do a cost over lifetime study before you choose types, but overall valve quality is highly important, and when asking for (preliminary?) bids you should ask for alternative types and quotes from all suppliers and a technical argumentation following the bid, and also references.
Very often today quotes tend or have to be ordered from cheapest offer, not highest quality of else (only seemingly) socalled 'equal types' from different manufacturors.
Advice: do not stress your inquiries with 'overspecification', stress instead lifetime and standtime importance and let the factory suggest or offer additions, materials and even types of solutions to give the best result.
An easy understood example: a 'gear' on a valve can be many different things, but in reality vastly different in operational torque, construction, materials and protection.
If you look at a commen valvesheet this will very often be described as 'with gear and (x) length extension.'
See the point?
If you do not ask for alternatives of highest available quality, or allow for this in competition comparison, you will end up with the cheapest gear available - not the best cost/lifetime solution.
- and for the valves it is even more complicated: small differences in construction can give large differences over 100 years, for instance exposed or not exposed inner bolts, and details on bolts and material quality.
Good luck!