Monday, September 28, 2015

Triple Offset Valves - Some Advantages and Considerations

Flowseal brand triple offset butterfly valve
Triple Offset Butterfly Valve
Courtesy Flowseal, Crane CPE
Industrial process control often involves the control of fluid flow, ranging from slurries or petroleum to highly refined liquids and gases. The enormous variety of application specifics has given rise to a wide range of valves with performance characteristics to match those requirements. One common valve type is the butterfly valve. In it's simplest form, it is a disc located in the path of fluid flow that is connected to a shaft. The disc rotates through a 90 degree arc to present either its face (valve closed) or its edge (valve open) to the fluid flow path. I wrote about some advantages and disadvantages of butterfly valves a couple months ago under the title "Is a Butterfly Valve Right for Your Application?".

There is a variant of the simple version of the butterfly valve that provides distinct advantages for many applications. Referred to somewhat officially as a triple offset butterfly valve, it can also be more commonly called simply a triple offset valve.

How is a triple offset butterfly valve different from a basic butterfly valve?


The triple offset valve does away with the centric alignment of the shaft and disc, using instead a shaft mounting arrangement that relocates the shaft axis off both the center of the disc and the center of the bore. This shaft positioning, while creating a larger flow obstruction in the fully open position, sets the disc movement path in the proper alignment to take advantage of the third offset, which is the sealing surface. Triple offset valves have a different seals than other butterfly valve variants. There is an angular sealing surface, the angle of which is determined by sectioning an imaginary right angle cone shape that extends along the bore. However, the apex of the cone does not lie on the center of the bore. This inclination of the seal cone constitutes the third offset. You can see an illustration of this description in the document included below.

What advantages might those differences bring to your application?


  • Triple offset valves have discs that do not contact the sealing surface until the valve is closed. This is in contrast to other butterfly valve designs, which have contact between the disc and resilient seals for part or all of the disc travel, along with the associated friction and wear.
  • Elastomer or other similarly resilient materials are not needed to provide a zero-leakage, bubble tight shutoff. Sealing is generally accomplished with metal-to-metal contact.
  • Friction free stroking of the valve disc. Actuator power requirements may be reduced.
  • All metal construction provides elements of corrosion and heat resistance not found in other butterfly valve designs with resilient seals.
  • This valve is torque sealed, not position sealed like other butterfly variants. Actuator torque forces the seal of the machined metal surfaces to produce tight shutoff.
  • No breakaway torque requirement, since the disc is not contacting resilient seals. 
  • Seating arrangement prevents overstroking of the valve, a potential problem with other butterfly valves.
Different manufacturers may have slightly different feature sets, but this should help you consider the benefits of this butterfly valve variant. Though its initial cost may be higher, the expected lower maintenance requirement, longer service life, and better performance may be well worth it. Talk to a valve product specialist about your application. I've written many times that combining your process expertise with the up to date product knowledge of a professional sales engineer will produce a positive outcome.


Tuesday, September 22, 2015

Mountain States Engineering Reference Library


Mountain States Engineering Reference Library
Industrial Process Control Product Reference Library
Mountain States Engineering 
Business is about getting things done.
In today's pressured environment, it's also about getting things done expeditiously. At Mountain States Engineering, we want our existing and prospective customers to know that we are here to help you get those things done....expeditiously. Our updated website includes a library of links and literature downloads for everything we sell. The goal is to help our fellow engineers in the industrial process measurement and control industry find answers and information quickly, anytime.

No registration, password, or revealing of personal information is required to access the information. Go to our website, select the menu bar item "Library" and you are in.

Mountain States Engineering is dedicated to support of industrial process engineers, technicians, and stakeholders of all types. With top flight products, problem solving, and support, Mountain States Engineering will be the group you turn to for industrial process control solutions. If you need anything not provided in the library, never hesitate to contact one of our engineering sales professionals.

Screen shot of Mountain States Engineering Library Page
Screen Shot for Mountain States Engineering Reference Library
No registration required

Monday, September 14, 2015

No Compressed Air? Use Water to Power Your Valve Actuator.

Hytork XLW Water Powered Valve Actuator
XLW Water Powered Valve Actuator
Courtesy Hytork
Air is everywhere, but very little of it is compressed for our use in powering a valve actuator. Sometimes, possibly at sites located remotely, a reliable source of compressed air is unavailable for process control valve actuation. Installing an air compressor at the site may be an option, but one with impact on the reliability of the installation deemed undesirable. One possible solution is a water powered valve actuator. With mains water available, pressurized within the range of 60 to 100 psi (4-7 bar), actuator power can be derived and valve operation successfully achieved.

Water always presents its own set of special considerations, not the least of which is that it tends to corrode most metals used in construction of actuator parts over time. Of additional concern are the particulates present in water systems which can cause premature deterioration of seals and scoring of cylinders in the actuator. Directional control solenoid valves will also function more reliably with a water supply free of larger particulates. While this is a concern, the solution is simply to place an inexpensive filter upstream of the devices, eliminating the contaminates from the water supply.

While it is possible to employ some "standard" actuators in a water powered setting, there are special adaptations that can be applied to common actuator design to better suit the use of water power. One manufacturer, Hytork, has done just that with their XLW Series of water operated actuators. The XLW Series is a water powered adaptation of the company's successful XL Series actuators. Special coatings are applied to critical parts to provide necessary protection for water applications. There are other differences between the compressed air and water versions of the actuator, detailed in the installation and operating instruction manual shown below. The manual is short enough to be read in a couple minutes (really, just a couple minutes) and provides useful and illustrative information about actuator construction, operating characteristics, and maintenance requirements.

Contact a valve application specialist for more information, or to discuss any of your fluid control application needs.


Monday, September 7, 2015

When is a Diaphragm Valve Your Best Choice?

Gemu Industrial Diaphragm Valve Metal Body Hand Operated
Hand Operated Metal Body Diaphragm Valve
Courtesy Gemu
Industrial process control, as a field of endeavor, covers an incredibly broad range of applications, all highly specialized in their own way. The control and handling of fluids is a prevalent activity in process control, leading to a wide variety of valves from which to choose for your application. Figuring out which flow control valve will best meet the needs of a particular application requires a detailed assessment of the physical elements to which the valve will be exposed, and under what conditions it will need to operate. In other words, know your process fluid, know your operating environment. A solid understanding of your process will make valve selection a simpler task, since there will likely be a small segment of your requirements able to be fulfilled by only one or two valve types.

When referring to valve types, common terminology generally describes the means utilized to control the flow. Some prevalent valve types, though certainly not an exhaustive list, include ball, plug, butterfly, diaphragm, gate, needle, and globe. Each of these basic designs have characteristics that make them more suitable than others for certain application conditions. Let's look at diaphragm valves.

A diaphragm valve controls fluid flow through the movement of a flexible membrane, unsurprisingly called a diaphragm. Numerous means can be employed to apply force to the diaphragm and a seal is created when the membrane compresses against a targeted portion of the valve body. A prominent feature of this valve type is the isolation, by the diaphragm, of the valve operation mechanism from the fluid. Two general body styles are available, referred to as weir and straight through. The weir design requires less extensive movement of the diaphragm than the straight through type, resulting in a longer expected life for the diaphragm. The straight through style, when open, provides little obstruction to the fluid flow and may be more suitable for some media.

Some diaphragm valve characteristics that might prove advantageous:

Pneumatically Operated Diaphram Valve, Plastic Body
Pneumatically Operated Diaphram
Valve, Plastic Body
Courtesy Gemu

  • Isolation of the valve operating mechanism from the fluid.
  • Design is easier to sanitize or sterilize in place than other valve types.
  • Throttling or shutoff service. Throttling generally limited to weir type.
  • Fast operation with powered actuators on weir type.
  • Valves can be lined with materials suitable for abrasive, corrosive, high purity, or other media.
  • Diaphragms available in wide variety of materials to suit application.
  • Leak tight shutoff.
  • Valves can be serviced in-line.
  • Suitable for many high purity applications with proper lining and membrane materials.

Diaphragm valve limitations that may be significant to your application:

  • Limited operating pressure range, when compared to many other valve types.
  • Flexing of diaphragm during operation limits usable life of the membrane and creates maintenance event.
  • Temperature range is limited to that of the membrane and liner material.
  • Range of available sizes is generally less than other valve types.
  • Manual operation is generally slow, requiring multiple turns of a handwheel.
Consider your process environment, consider your process fluid, consider if a diaphragm valve will provide the performance you need. I always recommend taking the time to discuss your application with a valve specialist. Their extensive knowledge base and application experience will enhance your solo valve selection performance.