月度归档： 2015年8月

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”.

Pressure Ratings

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

4”                            85PSI

Automation

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.

 Conclusion

Here in a nutshell is our opinion of the pluses and minuses of sanitary butterfly valve

Plus                                                                                       Minus

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.

In the sanitary process industry we have specified and applied thousands of sanitary pumps into a huge variety of high purity applications in the food, beverage and biopharmaceutical industries.  To identify the best sanitary pump for the application we rely on a number of analytical tools to assist in the process, including several pump sizing programs, pressure drop calculation software, manufacturers data as well as a lot of tribal knowledge we have developed over the years.

A major key in selecting the proper pump is to get as much application data as possible from the client.  Some clients have a vast knowledge of their product and application, others are much more limited, or sometimes not known at the time of request.  To assist in this process we have published a “Pump Application Datasheet” we request customers fill out to the best of their ability.  In this posting we thought we would review the data we ask for on the datasheet, what it means and why it is important.

• Application Description:  Understanding the application gives us a much better feel for what type of pump will do the job. We’re trying to figure out what you want to accomplish. Case in point:  An application for 20gpm @ 30PSI for a liquid transfer from one tank to another may use a very different pump than one at the same flow rate and pressure that is metering a fluid in a filling application.
• Fluid Description:  Different fluids will require different seal and elastomers. Different fluids also have different vapor pressures that can affect the suction conditions of a pump application.
• Viscosity:  Determining the viscosity of the fluid is critical.  Higher viscosity products won’t work with a centrifugal pump.  Extremely high viscosity fluids can create suction issues that need to be address on positive displacement pump applications. Viscosity is also important in calculating friction loss.
• Density/Specific Gravity:  This can affect centrifugal pump sizing criteria as well as horsepower requirements
• Temperature:  Both the process and cleaning temperatures are very important.  In a sanitary rotary PD pump such and a Waukesha Universal pump, higher temperatures may require the pump to have undersized rotors to prevent them from contacting the casing and front cover as the wetted parts of the pump expand under heat.  Temperatures can be a factor in proper elastomer selection.  Also, elevated temperatures affect the vapor pressure of a liquid and consequently the net positive suction head available.
• Flow Rate:  This one is pretty obvious
• Discharge Pressure:  This is critical in sizing centrifugal pumps in particular.  Proper sizing cannot be completed without a discharge pressure requirement.  Discharge pressure can also affect PD pumps in that all PD pumps have a maximum pressure rating.  The pressure also affects horsepower requirements.  If you don’t know you pressure requirement we will help you determine that using the discharge conditions listed further below on the datasheet.
• Is the Product Sticky or Abrasive?  This directly affects the mechanical seal material selection and whether or not a seal flush will be required.
• Suction Conditions:  A general overview of the suction piping can help to specify a pump that meets the net suction pressure. Are you coming out of a tank? How high off of the ground is the tank? Are there any suction flow restrictions?
• Discharge Conditions:  If you don’t know your discharge pressure requirements, give us the discharge conditions, i.e. a brief description of the process, the piping sizes, lengths and elevations.  We can use that data, along with the flow rate and viscosity information to generate your pressure requirements.  We have developed in house software that will do these calculations quickly and accurately.
• Seal Requirements:  If you know you seal requirements, i.e. single or double mechanical seal, seal materials and elastomers, tell us here.  If you need a recommendation we can do that using the fluid properties and temperatures on the upper part of the form.
• Motor Requirements:  There are a lot of choices in motors (see our earlier blog on different ratings and enclosures for motors).   This section allows you to specify your requirements.  If are unsure, we will walk you through the process.

TAG, Centrifugal Pumps, Sanitary PD Rotary Pumps, Sanitary Pumps