We have decided to write a series of blog posts on the various types of sanitary valves on the market covering their various methods of operations, their process benefits and limitations and their relative costs. Today we thought we would start with one of the most simple and least expensive examples, the sanitary butterfly valve.
Principles of Operation
The sanitary butterfly valve consists of a round, split stainless steel body and a stainless steel disc which is positioned in the center of the pipe. The disc (“butterfly”) has rods on the top and bottom that position the disk in the body and attach to a handle or actuator on the outside of the valve. A rubber donut like seat is positioned between the body and the butterfly. Turning the actuator/handle turns the disc either parallel or perpendicular to the flow. Different from a ball valve, this disc is permanently existing within the flow; consequently a pressure drop is always induced in the flow, regardless of valve position.
The valve seal is affected by the compression of the disk against the interior of the rubber seals. The rubber seal also seals the stem that attaches to the handle. Seal materials are normally available in EPDM, Viton and Silicone. Most sanitary butterfly valve manufacturers supply sizes from 1” through 4”.
The sanitary butterfly valve is clearly not a high pressure valve. Listed below are typical pressure ratings.
Size Pressure Rating @70 F)
1” 140 PSI
1 1/2” 140 PSI
2” 140 PSI
2 1/2” 110 PSI
3” 110 PSI
Most sanitary butterfly valves can be highly automated. Most manufacturers offer stainless steel pneumatic linear actuators for all sizes. Many offer different switch packages to mount to their actuators. Also, as they are ¼ turn valves, sanitary butterfly valves can be automated with double rack and pinion pneumatic actuators. There is a huge offering of different ¼ turn actuators on the market and an equally large offering of switch packs to go along with them. You can also fit electric ¼ turn actuators to them.
Other Sanitary Butterfly Valve Features and Benefits
While the operating principles of the butterfly valve are relatively straight forward, used ubiquitously in both in industrial and sanitary applications, each manufacturer has their own unique offerings. First, it’s important to understand that the butterfly valve market could be considered a commodity market. There is always a cheaper one out there. That being said, for best performance it is critical to select a high performing valve that suits your process requirements at a fair price.
One unique feature that customers should be mindful of are handle style and material type. Not every manufacturer offers 304 and 316L valves. MTRs and C of C’s can also be difficult to obtain. That’s where a good distributor can help you identify the best valve manufacturer for your application.
Continually, not every manufacturer offerings a wide variety of manual BFV handles. Some common handles that are available in addition to the standard quarter turn handle are the infinitely adjustable w/ lock out hub, a pad lock ready handle to lock the valve in place, 9 position handles, and even manual handles equipped with proximity switches.
Other considerations are end connections and valve footprint. Butterfly valves are generally wafer style valves, that being said, overall dimensions should still be verified. End connections available include Triclamp, I line, and butt weld. One important consideration if you will be welding a valve into the process line is maintaining the valve. While rarely done, you do not want to be cutting the valve out of the line every time you need to change the seat. One product offering by APV is a flanged type valve that is welded and then bolted into line to allowing benefits of a weld in valve with the ability to maintain the internal valve wafer.
Are Sanitary Butterfly Valves Clean?
The word sanitary has different meanings for different users. Are sanitary butterfly valves clean? Sort of, depending upon your application. The fact that they are offered with sanitary clamp ends and are made from polished stainless steel and FDA approved elastomers makes sanitary butterfly valves relatively clean. They are a straight through valve so they are relatively drainable. But in some industries, the seals around the stems on the disks are problematic. They often don’t get completely clean in a CIP cycle. So to truly clean the valves, they must be disassembled. Because of this, butterfly valves do not get 3A approval and you rarely see them in biopharmaceutical applications. The ASME BPE does not even address them. But we do see them in food and beverage applications on a daily basis. In the end, what is clean enough is often determined by the end user.
Here in a nutshell is our opinion of the pluses and minuses of sanitary butterfly valve
Inexpensive Cannot take high pressure
Easily automated Won’t completely clean during CIP
Quick Turn Around Difficult to find in ½” and ¾” sizes
Easy to repair/few spare parts
So that is our take on the sanitary butterfly valve. In future posts we will present overviews of the other commercially available sanitary valves including ball valves, diaphragm valves, seat valves, mix-proof valves as well as some of the more niche type valves.