Quarter Turn vs. Linear Industrial Valves

Linear control valve (Masoneilan)

Different types of valves are designed and applied for different roles in the process control. Linear valves and quarter-turn valves are two different types of valves utilized throughout industry to regulate and control fluid flow. Their design and construction reflect the intent of the valves application, with each being suited for a different class of use.

All valves operate by providing control of the position of an internal structure that impedes fluid passage to some degree. Generally, fluid flow at the valve can be characterized as one of three conditions, unrestricted (valve fully open), stopped (valve fully closed), and throttled (valve partially open). Process operational requirements will dictate whether just two (fully open and fully closed) or all three of those conditions will be needed. Many aspects of the fluid, the process, and the surrounding environment come into play when making an appropriate valve selection. Not always an easy task.

Solenoid valves are
a type of linear valve.
(ASCO)

Linear valves are generally characterized by their straight line motion that is used to position the valve plug, disc, diaphragm or other flow controlling element. The shape, size, and arrangement of the linear valve trim is generally intended to empower the operator with a range of flow through the valve. Through its positioning, the linear valve is able to regulate fluid flow at a slower, but more accurate rate. The valves can move a disk or a plug into an orifice, or push a flexible material, such as a diaphragm, into the flow passage. Gate valves and globe valves are common examples of linear motion valves. A solenoid valve also acts as a specialized type of linear valve. Linear valves are best applied as flow controllers, and are often suited for frequent operation and repositioning.

Ball valves are examples
of quarter turn valves.
(QTR)

Quarter turn valves traverse from fully open to fully closed by a 90 degree rotation of a shaft connected to the controlling element. Their comparatively simple operation allows for a design that is rugged and compact. One distinction of the quarter turn valves is their ability to quickly reposition from open to closed positions. Torque requirements to operate the valves are generally low to moderate. Ball and butterfly valves are examples of quarter turn valves.

Depending on the specific scenario, linear valves and quarter-turn valves are optimal choices for particular process environments. The accuracy of the linear valve and its ability to move in a linear fashion as opposed to a quarter-turn comes coupled with easy maintenance and decreased likelihood of cavitation. Both valve types enjoy widespread use and should generally not be viewed as competing designs for the same application. Each has a range of applications where it excels.

Contact Classic Controls for any industrial valve requirement by visiting https://classiccontrols.com or by calling 863-644-3642.

CSB Animation and Analysis of Torrance Refinery Explosion

The United States Chemical Safety Board investigates industrial accidents related to chemical processing. It is an advisory agency that provides recommendations for improving safety in chemical related operations.

Some accident events are illustrated with animated reenactment, along with the events determined to be contributory to the cause. In the case of the Torrance, CA refinery explosion, the animation shows how a worn valve that did not provide adequate shutoff was part of the string of events that ultimately led to disaster. Also of concern was the procedure followed in responding to the discovery of an unexpected condition indicating substantial process malfunction.

Fortunately, the flammable gases were detected by personal safety gear, enabling workers to clear the area before ignition occurred.

The video describes how the process operated and what failed. The key takeaway is that a single failure condition can reveal another that may have gone undetected. Also, operating under adverse conditions, trying to formulate strategy, is difficult and may not produce the most effective plan.

Industrial processing can be complicated and dangerous. Diligence in design, installation, and continuing maintenance of process equipment is part of the overall safety plan for every facility.

Consider your own process and where weaknesses may be lurking. Reach out to equipment and instrumentation vendors for advice and expertise regarding specific items of concern.

Valve Control Monitor Adapts to Wide Range of Actuators

Valve monitor control mounted using cast NAMUR bracket
Courtesy Westlock Controls

Combining control components from various manufacturers can sometimes facilitate the most effective or desirable solution to a process control challenge. This can certainly be true when configuring a control valve installation. Getting the feature set and packaging that best fit the application requirements can yield benefits throughout the useful life of the equipment.

Westlock Controls, manufacturer of valve control monitors, provides a convenient mounting bracket that adapts the installation of their valve control monitors to actuators employing NAMUR mounting patterns. The cast stainless steel bracket is provided in one of three available mounting kits, each complete with all necessary hardware.

More detail about the adapter bracket is found in the datasheet included below. For more information, share your control valve project requirements and challenges with process control valve experts, combining your own process knowledge and experience with their product application expertise to develop effective solutions.

Stainless Steel Cast NAMUR Mounting Bracket from Classic Controls, Inc.

Electro-Hydraulic Valve Acutators and Damper Drives

X2 Linear Acuator
Courtesy Rexa

Many valves employed in industrial processes are controlled from remote control stations. They may have a manual override mechanism in the form of a lever or handwheel, but the primary operating mechanism, or actuator, is a powered unit that responds to a control signal and provides necessary torque or linear force to position the valve appropriately.

There are several power sources used to drive valve positioning mechanisms, one of which is electro-hydraulic. This self-contained system provides the operating characteristics of a hydraulic drive system by incorporating an electrically powered fluid system into the actuator package.

The video below provides some additional detail. Consider the electro-hydraulic actuator as a candidate for your valve control applications, then share your requirements and challenges with product application experts. The combination of your process knowledge and their application expertise will yield an effective solution.

Limit Switches in Valve Actuators

Valve Position Sensor
Courtesy Westlock Controls

Limit switches are devices which respond to the occurrence of a process condition by changing their contact state. In the industrial control field, their applications and product variations are almost countless. Essentially, the purpose of a limit switch is to serve as a trigger, indicating that some design condition has been achieved. The device provides only an indication of the transition from one condition to another, with no additional information. For example, a limit switch triggered by the opening of a window can only deliver an indication that the window is open, not the degree to which it is open. Most often, the device will have an actuator that is positively activated only by the design condition and mechanically linked to a set of electrical contacts. It is uncommon, but not unknown, for limit switches to be electronic. Some are magnetically actuated, though most are electromechanical. This article will focus on limit switch designs and variants used in the control and actuation of industrial process valves.

Valves, devices used for controlling flow, are motion based. The movable portions of valve trim create some degree of obstruction to media flow, providing regulation of the passage of the media through the valve. It is the movement of critical valve trim elements that limit switches are used to indicate or control. The movable valve trim elements commonly connect to a shaft or other linkage extending to the exterior of the valve body. Mounting electric, hydraulic, or pneumatic actuators to the shaft or linkage provides the operator a means to drive the mechanical connection, changing the orientation or position of the valve trim and regulating the media flow. Because of its positive connection to the valve trim, the position of the shaft or linkage is analogous to the trim position and can be used to indicate what is commonly referred to as “valve position”. Limit switches are easily applied to the valve shaft or linkage in a manner that can provide information or direct functional response to certain changes in valve position.

In industrial valve terms, a limit switch is a device containing one or more magnetic or electrical switches, operated by the rotational or linear movement of the valve.

What are basic informational elements that can be relayed to the control system by limit switches? Operators of an industrial process, for reasons of efficiency, safety, or coordination with other process steps, may need answers to the following basic questions about a process control valve:

• Is the valve open? 
• Is the valve closed? 
• Is the valve opening position greater than “X”? 
• Has the valve actuator properly positioned the valve at or beyond a certain position? 
• Has the valve actuator driven the valve mechanism beyond its normal travel limits? 
• Is the actuator functioning or failing? 

Partial or complete answers to these and other questions, in the form of electrical signals relayed by the limit switch, can serve as confirmation that a control system command has been executed. Such a confirmation signal can be used to trigger the start of the next action in a sequence of process steps or any of countless other useful monitoring and control operations.

Applying limit switches to industrial valve applications should include consideration of:

• Information Points – Determine what indications are necessary or useful for the effective control and monitoring of valve operation. What, as an actual or virtual operator, do you want to know about the real time operational status of a valve that is remotely located. Schedule the information points in operational terms, not electrical switch terms. 
• Contacts – Plan and layout a schedule of logical switches that will provide the information the operator needs. You may not need a separate switch for each information point. In some cases, it may be possible to derive needed information by using logical combinations of switches utilized for other discrete functions. 
• Environment – Accommodate the local conditions and hazards where the switch is installed with a properly rated enclosure. 
• Signal – The switch rating for current and voltage must meet or exceed those of the signal being transmitted. 
• Duty Cycle – The cycling frequency must be considered when specifying the type of switch employed. Every switch design has a limited cycle life. Make sure your selection matches the intended operating frequency for the process. 
• Auxiliary Outputs – These are additional contact sets that share the actuation of the primary switch. They are used to transmit additional signals with specifications differing from the primary signal. 
• Other Actuator Accessories – Limit switches are often integrated into an accessory unit with other actuator accessories, most of which are related to valve position. A visual local indication of valve position is a common example. 

Switches and indicators of valve position can usually be provided as part of a complete valve actuation package, provided by the valve manufacturer or a third party. It is recommended that spare contacts be put in place for future use, as incorporating additional contacts as part of the original actuation package incurs comparatively little additional cost.

Employing a properly configured valve automation package, with limit switches delivering valve status or position information to your control system, can yield operational and safety benefits for the life of the unit. Good advice is to consult with a valve automation specialist for effective recommendations on configuring your valve automation accessories to maximize the level of information and control.

Pressure Regulator Valve or Back Pressure Regulator - Appropriate Application

One of many available configurations
for a pressure regulating valve.
Courtesy Cash Valve

Fluids move throughout processes, driven by pressure produced with mechanical or naturally occurring means. In many cases the pressure generated by the driving source is substantially greater than what may be desired at particular process steps. In other cases, the operation may dictate that a minimum pressure be maintained within a portion of the process train. Both cases are handled by the appropriate valve type, designed specifically to regulate pressure.

A pressure regulating valve is a normally open valve that employs mechanical means, positioning itself to maintain the outlet pressure set on the valve. Generally, this type of valve has a spring that provides a countervailing force to the inlet pressure on the valve mechanism. An adjustment bolt regulates the force produced by the spring upon the mechanism, creating an equilibrium point that provides flow through the valve needed to produce the set outlet pressure. A typical application for a pressure regulator is to reduce upstream or inlet pressure to a level appropriate for downstream processing equipment.

Back pressure valves are normally closed, operating in a logically reversed fashion to pressure regulators. Where pressure regulators control outlet pressure, a back pressure valve is intended to maintain inlet pressure. Similar internals are present in the back pressure valve, with the valve action reversed when compared to a pressure regulator. An inlet pressure reduction in the back pressure valve will cause the valve to begin closing, restricting flow and increasing the inlet pressure. A representative application for a back pressure valve is a multi-port spray station. The back pressure valve will work to maintain a constant setpoint pressure to all the spray nozzles, regardless of how many may be open at a particular time.

Both of these valve types are available in an extensive array of sizes, capacities, pressure ranges, and materials of construction to accommodate every process requirement. Share your fluid control challenges with a process control specialist. Combining your process knowledge with their product application expertise will produce effective solutions.

Pressure Regulating Valve - Type G-4 Cash Valve from Classic Controls, Inc.

High Performance Butterfly Valves Meet Special Application Challenges

High Performance
Butterfly Valve
ABZ Valve

Industrial process control applications can present stringent and challenging performance requirements for the physical equipment and components that comprise the process chain. The valves employed in fluid based operations need to be resistant to the impact of extreme fluid conditions, requiring careful design and selection consideration to assure proper performance and safety levels are maintained in a predictable way.

Industrial valves intended for extreme applications are generally referred to as severe service or high performance valves. While there are plenty of published and accepted standards for industrial valves, one does not exist to precisely define what constitutes a severe service valve.

So, how do you know when to focus valve selection activities on severe service or high performance valves, as opposed to those rated for general purpose? There are a number of basic criteria that might point you in that direction:

• Extreme media or environmental temperature or pressure
• High pressure drop operation that may cause cavitation
• Rapid or extreme changes to inlet pressure
• Certain types or amounts of solids contained in the fluid
• Corrosive media

Certainly, any of these criteria might be found in an application serviceable by a general purpose valve, but their presence should be an indicator that a closer assessment of the fluid conditions and commensurate valve requirements is in order. The key element for a process stakeholder is to recognize when conditions are contemplated that can exceed the capabilities of a general purpose valve, leading to premature failure in control performance or catastrophic failure that produces an unsafe condition. Once the possibility of an extreme or challenging condition is identified, a careful analysis of the range of operating conditions will reveal the valve performance requirements.

There are numerous manufacturers of severe service or high performance valves, each with specialized product offerings focusing on a particular performance niche. ABZ Valve manufactures high performance butterfly valves ranging from 2-48 inches and 150-600 psi. The valve design is ideal for manual or automated actuation, installed with a manual hand gear, electric actuator, or a pneumatic actuator. Seats are available as soft, metal, and fire safe, and body types include wafer, double flanged, and butt-welded. Construction materials include carbon steel and 316 stainless steel. A range of options and variants are available to customize the valve build to suit a replacement or new installation.

More information about the ABZ  Valve high performance offering is included below. You can always get more information and discuss your special requirements with a valve specialist. They have application experience and access to technical resources that can help with selecting the right valve components to meet your severe service and high performance applications.

Double Offset High Performance Butterfly Valves from Classic Controls, Inc.

New Website For Classic Controls

Home page on Classic Controls new website

Classic Controls, distributor of industrial process measurement and control equipment and instruments throughout Florida, Georgia, Puerto Rico, and the Caribbean, has a new website that is live now. The new site provides simple and rapid access to Classic Controls' represented lines and products, as well as the company's social media outlets, all organized in an intuitive and useful fashion to save users time in their search for solutions.

Visit the new site and see the products and capabilities of Classic Controls.

Electric Actuators for Industrial Valve Automation

Multi-turn Electric Actuator
AUMA

Electric actuators bring automation to industrial valve operation, allowing complex processes to be managed and controlled by remotely located control systems. There are other motive forces used for valve actuators, including hydraulic and pneumatic, but electric actuators carry their own particular set of operating characteristics that make them an advantageous choice for many applications.

Valve actuators are available in uncountable variants to suit every application scenario. There are three basic valve actuation motions.

• Multi-turn, with repeated rotations of the valve shaft needed to move the valve trim from fully open to fully closed. A gate valve is a multi-turn valve. These are also called linear, with respect to the motion of the closure element. The term "linear", in this case, refers only to the movement of the valve trim and not the flow characteristics of the valve.
• Part Turn, where a 90 degree rotation of the valve shaft produces a change from opened to closed. Ball valves are in this category.
• Lever, generally associated with damper control.

An electric actuator is a combination of motor and gearbox with sufficient torque to change valve trim position. A local self-contained control commands the motor and provides feedback to the process master controller regarding position, travel, torque, and diagnostics. Several interface options are available to facilitate communication between actuator and master controller.

There are numerous considerations to take into account when selecting an electric actuator.

• Torque needed to effectively operate the subject valve.
• Actuator enclosure type - wash down, hazardous area, dust, etc.
• Service area for the assembly - corrosive environment, temperature extremes, and more
• Valve movement - linear, multi-turn, part turn, lever
• Operation mode - open and close only, positioning, modulating
• Frequency or duty cycle - infrequent, frequent, or almost continuous positioning
• Communication - How will the local controller communicate with the central control system?
• Electrical - What electric power characteristics are available for operation?
• Protections - Motor overload, torque limit, others
• Process Safety - Among other things, what happens if power fails? 

There are certainly other elements to consider when applying an electric actuator for industrial use. You can see more detail about electric actuator operation and available configurations in the document included below. It is well illustrated and clearly describes the various aspects mentioned in this article. Share your valve and actuator requirements and challenges with product specialists, combining your process knowledge with their product application expertise to forge the most effective solutions.

Electric Actuators for Industrial Valve Automation from Classic Controls, Inc.