Basic Control Theory Tutorial

This basic control theory tutorial looks at on/off and continuous control modes. It introduces proportional, integral and derivative control actions and explains some of the terminology. Courtesy of Spirax Sarco and Mountain States Engineering and Controls.

Topics Include:

• On/off control
• Continuous control
• Proportional control
• The effect of adjusting the Proportional-band
• Reverse or direct acting control signal
• Gain line offset or proportional effect
• Manual reset
• Overshoot and ‘wind up’
• Derivative control - rate action
• PID controllers
• Hunting
• Lag
• Rangeability
• Turndown ratio

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DOWNLOAD THE TUTORIAL FROM THIS MSEC WEB PAGE

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Industrial Control Valve Basics

Understanding industrial control valve design and operation is very important if you work as a process engineer, a plant maintenance person, or if you design process control loops. Control valves are used extensively in power plants, pulp and paper mills, chemical manufacturing, petro-chemical processing, mining facilities, HVAC and steam distribution systems.

There are many types, manufacturers, body styles, and specialized features, but the they all share some basics operating principles. The video below explains components, operation, and fundamentals of how control valves operate.

https://mnteng.com
303-232-4100

Plug Valves - Right For Your Application?

Plug valves incorporate design features making them
a positive choice for many fluid process applications.
Image courtesy Fluoroseal, Inc.

There are common components to be found on almost every process system that involves fluid control. Regardless of the operation's scale, pumps, piping, tanks and valves are likely to be part of the system.

Valves, of which there are many types, provide control over the flow rate, direction and routing of fluids in a processing operation. Flow can be started, stopped or modulated between zero and full rate using a properly sized and configured valve. Some valves enable media flow to be diverted to a selection of outlets, in lieu of a single inlet and outlet pair. Specialized valves regulate inlet or outlet pressure, or prevent fluid flow from going in an undesirable direction. All of these capabilities are packaged into differing valve product offerings that present a very large selection array to a process designer or engineer.

Industrial flow control valve types are generally classified according to the structure or arrangement contained within the valve body that provides obstruction to fluid flow. Some of the common types are ball, butterfly, gate, globe, and plug. Surely, there are more valve types, and this article is not intended to list them all. Some of our previous blogs have discussed selection considerations for gate, ball and butterfly valves. This article will focus on one of the oldest valve types, the plug valve.

Plug valves, like ball and butterfly valves, span from fully open to fully closed positions with a shaft rotation of 90 degrees. The “plug” in a plug valve is installed in the flow path within the valve body and rotated by means of a stem or shaft extending to the exterior of the body. Plugs are often tapered toward the bottom and are fitted to a seating surface in the valve body cavity that prevents fluid from bypassing the plug. An opening through the plug, the port, can be shaped to provide particular flow characteristics. There are numerous variants of the basic plug valve which may make it suitable for particular applications. One common variant is the lined or sleeved plug valve, with an insert or interior lining of material that creates an isolating barrier between the valve body and the media. This allows use of less expensive materials for the body construction that may be otherwise subject to corrosion by exposure to aggressive media.

Positive attributes of plug valves.

• 90 degree rotation from open to closed provides fast operation.
• With proper configuration, can be well suited for frequent operation.
• Availability of corrosion resistant liner may provide comparative cost savings because valve body can be constructed of less expensive material.
• Design is simple and employs a low parts count.
• Valve can be serviced in place.
• Generally, low resistance to flow when fully open.
• Reliable leak-tight service due to tapered plug wedging action, replaceable sleeve, and injection of lubricant in some variants.

Potential issues of concern.

• Higher friction in the plug closure mechanism may require comparatively higher operating torque than other valve types.
• Without a specially designed plug, generally not well suited for throttling applications.
• Rapid shutoff delivered by plug design may not be suitable for some applications where hammering may occur.

Share your fluid control application challenges with a valve and automation specialist. Leverage your own knowledge and experience with their product application expertise to develop an effective solution.

Process Tuning

This sliding gate industrial control valve could operate
under the command of a tuned process control loop.
Image courtesy Schubert & Salzer

Controller tuning is a process whereby a controlling device in a process has a response characterized to the needs of maintaining a process condition within certain limits under a range of varying disturbances to the process. Established guidelines for automation standards exist so that every process control operator can experience the same standard of safety and maintenance in a way universally understandable. The International Society of Automation (ISA) promotes different tuning standards based on the particulars of the control process, such as temperature or liquid level control.

Liquid-level control loops are usually considered non-self-regulating processes. They require external moderation to remain uniform and for errors to either be mitigated or corrected. General rules which exist for adjusting and tuning loops for self-regulating process, such as temperature control, are often inapplicable to liquid level loops, making liquid level control loops somewhat unique in their tuning.

In order to address the counter intuitive nature of these process loops, start with a model of the loop’s ideal functionality. This can serve as a reference. After doing so, incorporate potential variables into the ideal loop and evaluate their impact on the model process. Checking equipment, then modeling the process dynamics, allows engineers to observe the manner in which the process reacts in relation to the target or goal performance.

Whereas other loops can be tuned via trial and error, liquid-level control loops should not be due to the nature of their reactions to controller input being different than that of other processes. Instead, the parameters for the control loop need to be carefully engineered, rather than specifically tuned. Liquid level loops are integrating processes, rather than self-regulating. A self-regulating process will, with no disturbances to the variables, reach an equilibrium at which the process value remains constant. Consider a non-self-regulating liquid level control loop where the fill valve is open. No equilibrium point will be achieved, just overflow. The distinction between the two types is key to understanding why tuning liquid level loops is a different process than self-regulating control loops.

Temperature and thermal loops, depending upon the process dynamics, present varying degrees of tuning challenge. PID temperature controllers are employed to adjust the heat input to a process to affect a change in, or maintenance of, a process temperature setpoint. Without proper tuning, the controller output and the resulting process performance can oscillate or be slow to respond, with a negative impact on process performance or yield. Many PID controllers have an auto-tune feature, some of which are more effective than others. The best results achievable by PID controller tuning are accomplished by defining a setpoint prior to the auto-tune process and starting the tuning procedure from a stable process condition. Tuning the controller in the same process environment in which it will operate can also be very helpful.

Share your process measurement and control challenges with experienced application specialists, combining your own knowledge and experience with their product application expertise to develop effective solutions.

Appropriate Application for Pressure Regulator Valve and Back Pressure Regulator

One of many variants of back pressure
regulator valves
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.

Keep Industrial Control System Cybersecurity Top of Mind

Industrial control system cyber security is a 24/7 operation 

Cybersecurity risks should be a concern to any business with an internet connection or data port. Smaller operators may feel their limited size and notoriety renders them generally immune to invasion. This is a falsehood. Every control system should be considered as a potential target. That said, paranoia and fear should not be your primary decision drivers. Cybersecurity is accomplished through awareness, diligence, and collaboration.

Even if you consider yourself a small and insignificant operator, it is useful to begin, then maintain, a connection to the conduits for industrial control system cybersecurity information. Develop your awareness of the potential for intrusion into your control system. Start to become knowledgeable about how cyber threats can impact your operation, how cyber intruders gain access. As you build your knowledge, it is likely you will find ways to improve your level of security without major change or expense.

The U.S. Department of Homeland Security houses the watchdog organizations for industrial control system cybersecurity. There is a group within the department that is dedicated solely to industrial control systems. The Industrial Control Systems Cyber Emergency Response Team, better known as ICS-CERT, works to reduce cyber intrusion risks for industrial control systems. The link for ICS-CERT should be your first stop when delving into industrial cybersecurity. The site provides links to many other resources and activities, all directly related to cybersecurity. You can sign up for newsletters, even receive alerts when new threats are uncovered.

Your steady progress of knowledge building will better prepare your organization for the cybersecurity challenges of the current environment, as well as those that will emerge in the future. A fact sheet from the National Cybersecurity and Communication Integration Center, providing some useful information on their functions and activities, is included below.

Any concerns you may have about the potential vulnerabilities of instruments or equipment currently in place should be shared with vendors as part of the evaluation of your current systems.

Fact Sheet From National Cybersecurity and Communications Integration Center from Mountain States Engineering and Controls

Pressure Regulating Valves

PIlot operated pressure regulator
intended for use in a steam system
Courtesy Pentair - Cash Valve

Many processes and equipment employ pressure regulating valves, the function of which is to maintain a desired outlet fluid pressure under varying conditions of supply pressure or outlet flow.

There are many pressure regulating valve variants, specifically designed to address a range of process conditions or offset a performance characteristic deemed undesirable in another design. Each variant has a suitable place in the range of possible applications, with cost, size, and complexity primary differences among the different offerings.

In its simplest form, a pressure regulating valve (PRV) consists of a flow restricting element, a measuring element, and a setpoint element. Outlet pressure applies force to the measuring element, often a diaphragm. As the outlet pressure increases, the diaphragm will move the flow restricting element toward the closed position, reducing the flow from the inlet. The restricting element is commonly a plug, disk, or some other recognizable valve trim arrangement. The setpoint element, likely a spring, provides a counterbalancing force on the diaphragm. When the force applied to the diaphragm by the outlet pressure reaches equilibrium with the counterbalancing force applied by the spring, movement of the restricting element stops. In this way, outlet pressure is controlled without the need for electric power, sensors, transmitters, or even a process controller. The entire assembly is self-contained and requires little attention.

Selecting a PRV for an application requires coordinated consideration of process performance range, desired conditions, and valve attributes to produce a selection that will provide the desired service. A valve improperly selected for an application may perform poorly. Some of the items to be considered include:

• PRV Type
• Body size
• Construction
• Pressure Ratings
• Maximum Flow Rate
• Outlet Pressure Range
• Accuracy
• Inlet Pressure
• Orifice Diameter
• Response Speed
• Turn-Down Ratio

A PRV is not a safety device, so independent means must be provided to protect the system from excessive pressure. Product specialists are a good source of help in selecting a properly sized and configured valve for an application. Share your fluid process control challenges with a product application specialist, combining your process knowledge with their product application expertise to develop effective solutions.

Stainless Steel Globe and Gate Valves For Industrial Process Control

Stainless Steel Gate Valve
CPE-Aloyco

Gate and globe valves see common usage throughout fluid processing industries. The correct procedure for valve selection includes an evaluation of the process media, environment, and how the valve will need to perform.

Gate valves, unless specially adapted, are intended for applications requiring only fully open or closed service. Their slow operation is advantageous at preventing hammering in the piping system and a fully open gate valve presents little pressure drop.

Globe valves are well suited for shutoff and throttling operation, controlling fluid flow at points between fully open or closed. The "Z" pattern of their fluid path does add some pressure drop.

Selecting the right valve construction material is an important element of a successful installation. Aloyco, a Crane brand, recommends consideration of several factors.

• Type of media
• Media temperature range
• Pressure range, including all possible conditions
• Environmental conditions which may affect the valve
• Extraordinary stresses to which the valve may be subjected
• Compliance with safety standards and/or piping codes

Stainless steel valve construction will provide an additional measure of corrosion resistance and may be a selection that extends the useful life of a valve.

More detail is included in the document included below. Share your fluid control requirements and challenges with a specialist, combining your process experience and knowledge with their product application expertise to develop effective solutions.

Stainless Steel Gate and Globe Valves For Industrial Process Control from Mountain States Engineering and Controls

Back Pressure Regulator or Pressure Regulator Valve, Appropriate Application

Pressure Regulator Valve
Courtesy Pentair 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 regulator valves for industrial process control from Mountain States Engineering and Controls

Back pressure valves for industrial process control from Mountain States Engineering and Controls

Operating Principle - Solenoid Valve

Solenoid magnetic field

A solenoid is an electric output device that converts electrical energy input to a linear mechanical force.

At the basic level, a solenoid is an electromagnetic coil and a metallic rod or arm. Electrical current flow though the coil produces a magnetic field, the force of which will move the rod. The movable component is usually a part of the operating mechanism of another device. This allows an electrical switch (controller) to regulate mechanical movement in the other device and cause a change in its operation. A common solenoid application is the operation of valves.

Solenoid valve basic parts

A plunger solenoid contains a movable ferrous rod, sometimes called a core, enclosed in a tube sealed to the valve body and extending through the center of the electromagnetic coil. When the solenoid is energized, the core will move to its equilibrium position in the magnetic field. The core is also a functional part of valve operation, with its repositioning causing a designed changed in the valve operating status (open or close). There are countless variants of solenoid operated valves exhibiting particular operating attributes designed for specific types of applications. In essence, though, they all rely on the electromechanical operating principle outlined here.
A solenoid valve is a combination of two functional units.

• The solenoid (electromagnet) described above.
• The valve body containing one or more openings, called ports, for inlet and outlet, and the valve interior operating components.

Flow through an orifice is controlled by the movement of the rod or core. The core is enclosed in a tube sealed to the valve body, providing a leak tight assembly. A controller energizing or de-energizing the coil will cause the valve to change operating state between open and closed, regulating fluid flow.

Share your control valve requirements and challenges with an application specialist. Combining your process application knowledge with their product expertise will produce the most effective solutions.

Eight Process Control Valve Selection and Application Criteria

Sliding Gate Control Valve
Schubert & Salzer

Fluid processes will employ control valves to regulate flow or pressure in between the extremes of fully open and fully closed. Their function and design is specifically different from shutoff valves, which are designed and intended for isolation of segments of a fluid system. Improperly applying or sizing a control valve can have consequences in operation, productivity, and safety ranging from nuisance level to critical. Here are some items that should always be part of your selection  and application consideration.

• A control valve is not intended to be a an isolation valve and should not be used for isolating a process segment. Make sure you select the appropriate valve for the function to be performed.
• Select materials of construction that will accommodate the media and the process conditions. Take into consideration the parts of the valve that come in contact with process media, such as the valve body, the seat and any other wetted parts. Operating pressure and temperature impact the materials selection for the control valve, too. Conditions surrounding the valve, the ambient atmosphere and specific local conditions that may expose the valve to corrosives should be included in your thinking.
• Install flow sensors upstream of the control valve. Locating the flow sensor downstream of the control valve exposes it to an unstable flow stream which is caused by turbulent flow in the valve cavity.
• Establish the degree of control you need for the process and make sure your valve is mechanically capable to perform at that level. Too much dead-band leads to hunting and poor control. Dead-band is roughly defined as the amount of control signal required to affect a change in valve position. It is caused by worn, or loosely fitted mechanical linkages, or as a function of the controller setting. It can also be effected by the tolerances from mechanical sensors, friction inherent in the the valve stems and seats, or from an undersized actuator.
• Consider stiction. Wikipedia defines it as "the static friction that needs to be overcome to enable relative motion of stationary objects in contact". This can be particularly evident in valves that see limited or no position change. It typically is caused by the valves packing glands, seats or the pressure exerted against the disk or other trim parts. To overcome stiction, additional force needs to be applied by the actuator, which can lead to overshoot and poor control.
• Tune your loop controller properly. A poorly tuned controller causes overshoot, undershoot and hunting. Make sure your proportional, integral, and derivative values are set.  This is quite easy today using controllers with advanced, precise auto-tuning features.
• Avoid oversizing control valves. They are frequently sized larger than needed for the flow loop they control. If the control valve is too large, a small percentage of travel or position change could produce an unduly large change in flow, which in turn can make stable control difficult. Unstable control can result in excessive movement and wear on the valve. Try to size a control valve at about 70%-90% of travel.
• Think about the type of control valve you are using and its inherent flow characteristic. Different types of valves, and their disks, have very different flow characteristics. The flow characteristic can be generally thought of as the change in rate of flow in relationship to a change in valve position. Globe control valves have linear characteristics which are preferred, while butterfly and gate valves tend to have non-linear flow characteristics, which can cause control problems.  In order to create a linear flow characteristic through a non-linear control valve, manufacturers add specially designed disks or flow orifices which create a desired flow profile.

These are just a few of the more significant criteria to consider when selecting and applying a process control valve. Consider it good practice to discuss your selection and application with a product application expert to confirm your final selection. Combing your process knowledge with their application expertise will provide the best outcome.

Pressure and Temperature Switches for Demanding Industrial Applications

Industrial Temperature Switch
for Hazardous Location
Courtesy CCS

Industrial process control applications, by their very scale and nature in financial, operational, and safety terms, call for rugged and well performing devices and equipment. In the area of temperature and pressure related control, switches are often employed to achieve or respond to an enormous range of possible conditions.

Temperature and pressure switch reliability is especially critical in applications located within hazardous zones or locations. Custom Control Sensors (CCS) manufactures pressure and temperature switches for the most demanding applications in hazardous environments.

Products are designed to provide high cycle life through the use of a Belleville spring to reduce mechanical wear on the switch element. The switches have no moving parts, other than the actuating mechanism which has a limited movement of 0.01 inch.


CCS products for hazardous locations are routine deployed on

• Oil Platforms
• Pump Control
• Refineries
• Control and Annunciator Panels
• Relay Alarm Systems
• Pipelines
• Gas/Steam Turbines
• Oil Filtration

Included below is a short form catalog illustrating the CCS line of pressure and temperature switches for hazardous and non-hazardous locations. In addition to the suitability of the industrial switches for use in hazardous areas, CCS temperature and pressure switches exhibit these main features:

• High Cycle Life
• Wide Range of Set Points
• Protection Against Environment
• High Over-Pressure Capability
• No calibration needed
• Maintenance free
• High vibration resistance

Consider your temperature and pressure related applications and share your challenges with a product application specialist for the best solutions.

Temperature and Pressure Switches For industrial Applications from Mountain States Engineering and Controls

Solenoid Valves - A Staple of Process Control

Series I Solenoid Valve
Courtesy Granzow

The Granzow line of fluid control products for industrial and commercial application includes an extensive array of solenoid valves that are suited for a wide variety of applications. The short video below illustrates the company's offering that covers a broad range of flow rates, orifice and connection sizes, materials of construction, and control options.

More detailed product and application information is available from product specialists. Share your application challenges and work together to develop the best solution.

Video Tutorial of Direct Acting and Pilot Operated Pressure Relief Valve Operation

Safety Valve

Here is a clear and well illustrated tutorial video detailing the operational principals of pilot and direct acting pressure relief valves.

There are many available configurations of pressure relief and safety valves, each tailored to accommodate a particular set of application criteria. Understanding how these valves work is important to their proper selection and application to industrial processes and their control.

Product performance and selection information, as well as application assistance, is available from product specialists.

LOGIIC - Confederation of Government & Industry for Cybersecurity

Oil and gas industry partners with US DHS for cybersecurity

In response to the challenges presented by malicious or mischievous cyber operatives, a number of organizations joined together to collaborate in the design, testing, and implementation of tools and techniques to protect critical industrial systems on a global scale. LOGIIC (Linking Oil and Gas Industry to Improve Cybersecurity), as its name implies, focuses on the oil and gas industry. We should all know, however, that a substantial portion of the automation and process control devices we regularly utilize throughout many industries today were originally developed in the oil and gas industry, where the operational scale and risk level are sufficiently high to justify the costs of developing new technology, methods, and equipment.

LOGIIC participants include the Automation Federation, which brings the resources of world class device and software manufacturers to bear on cybersecurity issues of the day. The Cyber Security Division of the Science & Technology Directorate in the US Department of Homeland Security is also involved. Currently, five major oil companies are members.

Since its inception, LOGIIC has successfully completed eight major projects, with plans for many more. Upon completion of selected projects, LOGIIC delivers public reports to help elevate best practices across the entire industry. Both the member companies and the government are putting funds towards these projects which benefits not only the private sector, but also the public interest. Companies are applying the results within their organizations, because it helps bridge the gap between information technology and the industrial-environment sides of the organization.

LOGIIC is an organization that conducts activities and disseminates information that can be useful throughout your own organization and that of your customers and suppliers in the industrial process control field. Below is a video highlighting the organization and its work.

Developing a Useful Alarm Strategy for Industrial Process Control

Pharmaceutical process operation

Industrial process control operators and designers have the capability to measure many aspects of machine operation and process performance. Determining the elements to measure, method of measurement, and how to handle and process the derived information can be challenging, but can also impact the security, performance, and safety of an operation. A plan for monitoring, reporting, and responding to abnormal process conditions, if properly developed and executed, can yield real benefits to a process operator. A protocol that is not well conceived may produce a negative operational impact by creating events that unnecessarily draw resources away from productive endeavor. That protocol, or plan, is often referred to as an alarm plan.

There are numerous forces that can influence the development and implementation of an alarm plan. Each operation must incorporate its own set of external regulatory requirements, internal procedures and policies into a complete alarm protocol. Distilling that macro description down to a workable set of procedures and response tasks is where the real work begins. There is, however, a basic framework that can help organize your thinking and focus on what is most important.

• What parameters define the process or operation?
  Produce a schedule of every non-human element that is required to make the process function. This will require drilling down through every machine and material that is part of the operation. Expect the schedule to be extensive, even huge. If it is not, consider that your analysis may not be reaching deep enough. The goal here is to create an overview of what makes the process work and provide a tool for systematically studying the process elements and gleaning possible commonalities or relationships among them. Consider disregarding things that cannot be measured, since that prevents the derivation of data for evaluation. Review the completed schedule and decide which parameters shall be measured and evaluated for proper performance.
• What level of measurement is needed for each monitored parameter?
  An assessment of the needed accuracy, frequency, and resolution for parameter measurement will help define the requirements for instrumentation or other devices used to monitor a particular item. The goal is to make sure the monitoring device is capable of detecting and delivering information of sufficient quality to make decisions.
• Define the limits of acceptability for each monitored parameter.
  Until the endpoint of the process or operation, each step is likely dependent in some way on previous steps. The output of each step becomes the input of the next. While this, in many cases, may be an oversimplification, it is important to consider the relationships between the
   tasks and operations that comprise the process. Monitored parameters should relate to the successful completion of a process step, though not necessarily be a direct indicator of success. The maintenance of the parameter within certain bounds may be used as an indicator that a component of successful completion was properly attained. Defining limits of acceptability may involve an element of subjectivity and will likely be customized to accommodate the process. Each organization shall evaluate their operation and determine limits based upon intimate process knowledge and experience.
• Define abnormal operation for each monitored parameter.
  Abnormal operation may not necessarily be any value not within what is considered acceptable. Consider abnormal to be the range of values that would be cause for notification of the operator, or even automated or human intervention. Note that the definition of unacceptable or abnormal operation might appropriately include filters or defined relationships with other parameters. An example of a simple filter is a time delay. If the measured variable exceeds the specified limit for 2 seconds, it make not be significant. If the threshold is exceeded for 2 minutes, it may be cause to take action. As with the limits of acceptability, developing the definition of abnormal operation for each parameter will be customized for each process.
• Provide a defined response for every alarm occurrence.
  If it is important to monitor something, then it is likely important to do something when things get out of hand. Human executed alarm response should be concise and uncomplicated, to reduce the probability of error. Automated response should be designed in a manner that provides for functional testing on a regular basis. The scope of the response will be specific for each process, with the level of response depending upon factors determined by the process operators. Response can be as simple as annunciating the condition at a monitoring station, or as dire as shutting down part or all of the process operation.
• Review every alarm occurrence
  Each alarm event should be logged and reviewed. Consider whether the event detection and response was adequate and beneficial. If the results were less than expected or desired, assess whether changes can be made to provide improved results in the future. The alarm plan is unlikely to be perfect in its first incarnation. Be prepared to reevaluate and make changes to improve performance.

The exercise of developing a comprehensive alarm plan will help to build understanding of process operation for all involved parties. This article is but a brief synopsis of the subject, intended to get the reader on the path of developing a useful alarm plan. Your alarm plan should an extension of process operation decision making, and have a goal of enhancing safety and reducing loss.   

A Framework For Thinking About Process Instrument Protection

Provide adequate levels of protection for instruments
and controls that keep your process running

The performance of every process is critical to something or someone. Keeping a process operating within specification requires measurement, and it requires some element of control. The devices we use to measure process variables, while necessary and critical in their own right, are also a possible source of failure for the process itself. Lose the output of your process instrumentation and you can incur substantial consequences ranging from minor to near catastrophic.

Just as your PLC or other master control system emulates decision patterns regarding the process, the measurement instrumentation functions as the sensory input array to that decision making device. Careful consideration when designing the instrumentation layout, as well as reviewing these five common sense recommendations will help you avoid instrument and process downtime.

Process generated extremes can make your device fail.

Search and plan for potential vibration, shock, temperature, pressure, or other excursions from the normal operating range that might result from normal or unexpected operation of the process equipment. Develop knowledge about what the possible process conditions might be, given the capabilities of the installed process machinery. Consult with instrument vendors about protective devices that can be installed to provide additional layers of protection for valuable instruments. Often, the protective devices are simple and relatively inexpensive.

Don't forget about the weather.

Certainly, if you have any part of the process installed outdoors, you need to be familiar with the range of possible weather conditions. Weather data is available for almost anywhere in the world, certainly in the developed world. Find out what the most extreme conditions have been at the installation site....ever. Planning and designing for improbable conditions, even adding a little headroom, can keep your process up when others may be down.

Keep in mind, also, that outdoor conditions can impact indoor conditions in buildings without climate control systems that maintain a steady state. This can be especially important when considering moisture content of the indoor air and potential for condensate to accumulate on instrument housings and electrical components. Extreme conditions of condensing atmospheric moisture can produce dripping water.

Know the security exposure of your devices.

With the prevalence of networked devices, consideration of who might commit acts of malice against the process or its stakeholders, and how they might go about it, should be an element of all project designs. A real or virtual intruder's ability to impact process operation through its measuring devices should be well understood. With that understanding, barriers can be put in place to detect or prevent any occurrences.

Physical contact hazards

Strike a balance between convenience and safety for measurement instrumentation. Access for calibration, maintenance, or observation are needed, but avoiding placement of devices in areas of human traffic can deliver good returns by reducing the probability of damage to the instruments. Everybody is trained, everybody is careful, but uncontrolled carts, dropped tools and boxes, and a host of other unexpected mishaps do happen from time to time, with the power to inject disorder into your world. Consider guards and physical barriers as additional layers of insurance.

Know moisture.

Electronics must be protected from harmful effects of moisture. Where there is air, there is usually moisture. Certain conditions related to weather or process operation may result in moisture laden air that can enter device enclosures. Guarding against the formation of condensate on electronics, and providing for the automatic discharge of any accumulated liquid is essential to avoiding failure. Many instrument enclosures are provided with a means to discharge moisture. Make sure installation instructions are followed and alterations are not made that inadvertently disable these functions.

Developing a thoughtful installation plan, along with reasonable maintenance, will result in an industrial process that is hardened against a long list of potential malfunctions. Discuss your application concerns with your instrument sales engineer. Their exposure to many different installations and applications, combined with your knowledge of the process and local conditions, will produce a positive outcome.

Valve Preparation For Oxygen or High Purity Service

Oxygen is used extensively throughout a wide range of industrial processes. Medical, deep-sea, metal cutting, welding, and metal hardening are a few examples. The steel industry uses oxygen to increase capacity and efficiency in furnaces. As a synthesis gas, oxygen is also used in the production of gasoline, methanol and ammonia.

Odorless and colorless, oxygen is concentrated in atmospheric air at approximately 21%. While O2, by itself, is non-flammable, it vigorously supports  combustion of other materials. Allowing oils or greases to contact high concentrations of oxygen can result in ignition and possibly explosion. Oxygen service preparation of an industrial valve calls for special cleaning processes or steps that remove all traces of oils and other contaminants from the valve to prepare for safe use with oxygen (O2). Aside from the reactive concerns surrounding oxygen, O2 preparation is also used for applications where high purity must be maintained and valves must be free of contaminants.

Gaseous oxygen is noncorrosive and may be used with a variety of metals. Stainless steel, bronze and brass are common. Liquid oxygen presents unique challenges due to cryogenic temperatures. In this case, valve bodies, stems, seals and packing must be carefully chosen.

Various types of valves are available for oxygen service, along with a wide array of connections, including screwed, socket weld, ANSI Class 150 and ANSI Class 300, DIN PN16 and DIN PN40 flanged ends. Body materials include 316 stainless steel, monel, bronze and brass. Ball and stem material is often 316 stainless steel or brass. PTFE or glass filled PTFE are inert in oxygen, serving as a common seat and seal material employed for O2 service.

Common procedures for O2 service are to carefully deburr metal parts, then meticulously clean to remove all traces of oil, grease and hydrocarbons before assembly. Valve assembly is performed in a clean area using special gloves to assure no grease or dust contaminates the valve. Lubricants compatible with oxygen must be used. Seating and leakage pressure tests are conducted in the clean area, using grease free nitrogen. Specially cleaned tools are used throughout the process. Once assembled, the valves are tested and left in the open position. A silicone desiccant pack is usually inserted in the open valve port, then the valve ports are capped. A warning label about the desiccant pack's location is included, with a second tag indicating the valve has been specially prepared for oxygen service. Finally, valves are individually sealed in polyethylene bags for shipment and storage. Different manufacturers may follow slightly differing protocols, but the basics are the same. The valve must be delivered scrupulously contaminant free.

The O2 preparation of valves is one of many special production variants available to accommodate your special application requirements. Share your valve requirements and challenges with a valve specialist to get the best solution recommendations.

Multiport Valve Block Demonstration Video

Stainless Steel Multiport Valve Block
Courtesy Gemu

Industrial fluid processing operations routinely include distribution, mixing, and dosing operations on the path to a finished product. With numerous valves, fittings, pipe sections, supports, and other components required to form the fluid path combinations needed to accomplish the process goal, designs can easily become complex and installations unwieldy. Greater parts count puts upward pressure on the probability and frequency of leakage or other types of failures that will divert resources from otherwise productive tasks.

The traditional method of fluid routing through a process may have involved one or more valve stations consisting of manually constructed piping and valve assemblies with numerous fittings, pipe sections, and support structures. These assemblies are often sizable, due to the nature of their manual assembly and required space allowances for field service and maintenance.

Designers and builders of fluid processing equipment should consider an alternative with some distinct advantages. 

A multiport valve block can combine numerous valves into a single compact unit. By doing this, large counts of fittings, pipe lengths, and supports are eliminated, substantially reducing the parts count and number of potential failure points. Of equal importance is the reduction in the required installation space provided by the compact form factor of  the valve block. There is also potential for reduction of dead leg space and volume of fluid retained in portions of the system.

Muliport valve block starts with a solid metal block
which is machined and polished to finished form.
Courtesy Gemu

There are endless configurations of multiport valve blocks that can be designed and configured to match the requirements of simple to highly complex valve networks. Materials of construction range from plastics to stainless steel. Variants are suitable for CIP and SIP operations.

The video below shows real world (not animated) functioning of a demonstration unit designed for a mixing operation. Essentially, a multiport valve block allows the installation of a whole lot of valves in a comparatively small space, reducing parts count and associated risk.

Watch the short video. Think about how this modern and effective method of valve networking can bring benefits to your operation. There is much more application detail available from product application specialists. Share your process challenges with them and work together to generate the best solutions.

Chemical Flow Meters for Hazardous Environments

Chemical Flow Meters for Industrial Process Measurement
Courtesy ISTEC

ISTEC Corporation’s Aquametro Domino line of Chemical Flow Meters provide accurate measurement of water and liquid chemical flows using rotary piston or vane wheel technology. Versions of the instruments are designed for use in safe and hazardous areas (ATEX). The Domino line has flexible mounting configurations to minimize installation space, and is suitable for conductive or non-conductive liquids. Proper operation and accuracy of the instrument is not diminished by flow disturbances. The rugged units are manufactured in a wide array of sizes and configurations to accommodate every application.

Review the product literature below, or contact a product specialist to discuss your water or liquid chemical flow measurement requirement.

ISTEC Aquametro Chemical Flowmeter - Domino Series from Mountain States Engineering and Controls