Showing posts with label Southern Illinois. Show all posts
Showing posts with label Southern Illinois. Show all posts

Monday, July 16, 2018

Why Is Monitoring the Amount of Moisture in a Steam System So Critically Important?

Wet steam is a costly problem across many industries. It causes product quality issues with batch rejection, wet packs and wet loads in sterilizers. Wet culinary steam can make food grade quality of product impossible. Carbon dioxide in a system with wet steam creates carbonic acid that damages pipes. A slug of water causes water hammering, which is destructive and can be deadly. Wet steam causes many flowmeters to be inaccurate, so that if you buy steam from a third party, you may be paying for water rather than steam. Water abrades like sand in a steam pipe and will erode pipes, elbows, valves and other components. Wet steam reduces heat transfer. Wet steam can damage turbines. And wet steam causes thermal stress as condensate cools down.

In fact, steam quality typically refers to the amount of water in the steam, which is also known as dryness fraction. Saturated steam is a mixture of steam and water. The water is often in the form of un-vaporized micro droplets. Dryness fraction is a ratio. The mass of the steam to the mass of the biphasic mixture of water and steam. Part of the difficulty in measuring the steam dryness fraction is that steam systems are dynamic. The steams is moving through the components and conditions change second-by-second. Within this complex system there are many things that contribute to water in the steam. For example, the bursting bubbles from the surface of the boiling water expels small droplets into the flow of steam. Or if there is a sudden increase in demand for steam that reduces pressure above the water, lowering the boiling point and increasing the violence of bubbling. This is sometimes called priming or carryover. Other forms of carryover include water in the system, because the water level in the boiler is too high. Or high concentrations of impurities in the boiler water that reduce the surface tension and so increase the agitation of the water surface. Impurities can also cause the formation of a stable foam above the water surface. This foam causes slugs of water to be intermittently discharged from the boiler along with the steam. Even poor insulation in pipes and valves leads to water in the steam as heat is lost and steam condenses. A steam trap might fail closed, particularly at the bottom of a separator, increasing the amount of condensate in the pipes. The design of steam pipe work and steam traps may be inadequate to handle condensate, or a steam separator may be defective.
Steam QM-1
Armstrong Steam QM-1

Any of these things individually or in combination can cause a problem with dryness fraction. Monitoring the dryness fraction of steam has long been a manual process, time-consuming, inconsistent, unreliable, and presents inherent safety and accuracy risks. Control of your steam quality depends on having consistent, accurate, timely information, and that's where the Armstrong Steam QM-1 comes in.

The Armstrong steam quality monitor steam QM1 provides you with data logging and remote monitoring capabilities. The Steam QM-1 monitors and measures dryness fraction and alerts you of steam quality problems. The video below explains how.

With monitoring by the Steam QM-1 you can:
  • Manage process quality when injecting steam 
  • Ensure foodgrade quality of steam when producing culinary steam 
  • Check dryness of outsource steam 
  • Avoid water hammer 
  • Oversee traps and separators effectiveness 
  • Monitor boiler carryover 
  • Avoid erosion in valves regulators etc 
  • Protect turbine low pressure saturated steam stages 
For more information contact Mead O'Brien by visiting https://meadobrien.com or by calling (800) 892-2769.

Saturday, June 30, 2018

Metso Neles Flow Control Solutions: Valves, Actuation, and Automation

Neles Flow Control SolutionsNeles Controls, a unit of Metso Automation, is a manufacturer of high quality rotary control valves,
on/off valves, actuators, positioners, emergency shutdown valves (ESD), digital valve position
control products and severe service specialty valve products.

Their product mix includes:
  • Control Valves
  • Globe Control Valves
  • On-Off Valves
  • ESD Valves, Engineered Valves
  • Smart Positioners 
  • Analog Positioners
  • Pneumatic Actuators
  • Electric Actuators
  • Limit Switches
Below is their comprehensive Flow Control Solutions catalog. You may review the embedded document, or download a PDF version of the Neles Flow Control Solutions here.

Saturday, June 23, 2018

Mead O'Brien: Total Process Control Solutions Provider

As experts in valve automation, process instrumentation, steam systems and hot water systems, Mead O'Brien provides solutions to industrial companies in Missouri, Kansas, Nebraska, Iowa, Oklahoma, Arkansas, Texas Panhandle, Southern Illinois, Western Kentucky, and Southwest Indiana.

Specializing in Power, Refining, Chemical, Food & Beverage, Oil & Gas, Heavy Industrial, Water & Wastewater, and HVAC,  Mead O’Brien provides it's customers outstanding products, superior customer service, a team of highly skilled technicians, and decades of application experience.

These assets, in combination with their track record of successful outcomes and loyal customer base, positions Mead O'Brien as the perfect partner for all your process control equipment needs.

Give Mead O'Brien a call today.

https://meadobrien.com
(800) 892-2769

Wednesday, June 13, 2018

Electric Valve Actuation

Limitorque Electric Valve Actuator
Limitorque Electric Valve Actuator
Electric actuators use electrical power to actuate a valve. While most of the basic technology used in electric actuators has been around since the 1930s, decades of incremental improvement have significantly increased their functionality while dramatically reducing their cost. In recent years, these advances have reached a tipping point that makes electric actuators the first choice for a wide variety of applications.

Pros
  • Electric power is relatively inexpensive, easy to manage, and normally available to most industrial sites. The capital cost of electric actuators is typically cheaper per equivalent unit of torque/thrust output. They’re also cleaner and safer to operate. 
  • Electric actuators can provide superior positioning accuracy for control or modulating valve functions, which can include provisions for a high degree of process monitoring, data logging and information feedback. 
  • All necessary control functions are integral to electric actuators, reducing capital costs. 
  • Electric actuators significantly reduce control wiring costs by enabling distributed control. They simplify control logic by integrating control commands and feedback into customer SCADA or DCS systems. (Traditional electromechanical control systems require a dedicated wire for each command and feedback signal, leading to cable bundles with seven or more cores as minimum for each actuator. By contrast, a typical bus system can use one twisted pair wire in a daisy chain configuration to carry all required input and output signals.) 
  • As torque and thrust requirements increase, electric actuators weigh less and have smaller footprints compared to pneumatic actuators. 
  • Electric actuators may be combined with external gearboxes to produce extremely high output thrust and torque values.
Cons
  • With the exception of a few specific configurations, electric actuators can’t guarantee a fail-safe stroke but will “fail in the last position.” (Fail-safe stroke refers to an actuator’s ability to move a valve to a predefined safe position when power fails).
  • Electric actuators have more complex and sensitive components than the mechanical parts used in other types of actuators. Electronic technology also requires periodic refreshing to keep pace with component changes and improvements.
  • Beyond a certain size/torque range, electric actuators are less cost-effective and generally have limitations in operating speed when compared to pneumatic and hydraulic actuators.
  • In hazardous areas with potential exposure to explosive process media, electric actuators require more specific certifications and construction features to be considered safe for use.
Recommended applications

Electric actuation is the first choice for most oil and gas applications. They’re ideal for general process valve automation, non-critical applications, and light-duty modulating applications (generally up to 1200 starts per hour), although some can modulate continuously up to 3600 starts per hour.

Tuesday, May 29, 2018

Basic Set up of the Schneider Electric / Foxboro LG01 Guided Wave Radar Level Transmitter

Foxboro LG01 Guided Wave Radar Level TransmitterThe Foxboro Model LG01 Radar level measurement transmitter provides very accurate and reliable level measurement for the widest choice of installation and application.

Guided Wave Radar Technology 

Electromagnetic pulses are emitted and guided along a probe. These pulses are reflected back at the product surface. The distance is calculated by measuring this transit time. This device is perfect for high-end applications. It is suitable for applications with foam, dust, vapor, agitated, turbulent or boiling surfaces with rapid level changes.

This video demonstrates the quick set up of the instrument. 

Tuesday, May 22, 2018

What are In-line Drain Separators?

In-line (drain) separators
In-line (drain) separator.
(Armstrong)
Condensate in steam and air piping reduces thermal efficiency, causes water hammer, corrodes equipment such as valves and pipes, and causes other problems.

In-line (drain) separators separate condensate efficiently by using the centrifugal force of steam or air created by introducing it into a specifically shaped path. Because of the simple structure of the drain separators, pressure loss is minimized, enabling clean, dry steam or air to be fed to equipment.

When steam or air flow enters the drain separator, centrifugal force is generated in the fluid because of the device’s internal structural design. The fluid drains along the wall because of the difference in specific gravity with steam or air, eventually striking the baffle. The baffle guides the fluid to the drain outlet and to the trap, which drains it. As a result, small dirt particles and condensate are separated and removed from the system through the bottom drain.

Features:
  • Cyclone structure maximizes liquid separation efficiency
  • Pressure loss is extremely low
  • No moving parts means no breakdowns

Sunday, April 29, 2018

Armored Liquid Level Gauges

Armored Liquid Level Gauge
Armored Liquid Level Gauge
(Jerguson)
Sight glass liquid level gauges are a mainstay of fluid processing operations that store raw materials, intermediate, or final product in tanks and other vessels. Having a direct visual indication of fluid level at the tank enhances safety and provides the all important data point about what is happening inside the tank.

These level gauges are installed on the exterior of the tank, exposed to whatever environmental or operational hazards existing or occurring at the location. Armored level gauges are appropriately named because of their construction. They are designed to resist impact and mechanical stress, as well as a range or environmental conditions.

Armored Liquid Level Gauge
Reflex Gauge
There are generally two versions of armored level gauges, reflex and transparent. The names refer to way in which light is handled by the gauge to reveal the liquid level. One manufacturer of armored level gauges and other level instruments, Clark-Reliance, provides a good description of the two gauge types.

"Jerguson® Reflex Level Gauges are ideal for clean total level indication applications for refining, petrochemical and general use applications. The reflex prisms are molded and polished to provide a crisp black-silver bi-color indication of the fluid level. As light passes into the reflex glass, if there is fluid present, the light continues through the glass and reflects off the back of the level gauge, providing a black color for fluid level regardless of the actual color properties of the process fluid. If fluid is not present, the light is reflected off the glass back towards the user, providing a shiny silver or mirror-like appearance to indicate vapor space."

Armored Liquid Level Gauge
Transparent Gauge
"Jerguson® Transparent Level Gauges are selected for interface level indication, dirty service or any application that requires the use of a shield to protect the glass from corrosion. A transparent gage is also known as a “thru-vision” gauge since the gauge is constructed with two pieces of flat polished glass assembled on opposite sides of the level gauge chamber. Since the user can see straight through the gauge, it is also easy to view the fluid properties, such as color, whereas this would not be possible with a reflex gauge. The use of an illuminator is always recommended on a transparent gauge."

Selecting an armored level gauge is an exercise in preparing for known and unknown events that might disable your ability to directly read fluid level. Armored level gauges are employed extensively in chemical, petrochemical, and other industries where reliability under challenging conditions is essential. Wherever there are mechanical hazards, an armored level gauge may ultimately prove to be cheap insurance against downtime or delay.

Share your level measurement challenges with a product application specialist. Combine their product expertise with your process knowledge to produce an effective solution.

Thursday, April 19, 2018

Wireless Process Control Instrumentation

Wireless Process Control Instrumentation
Cost cutting is a fact of life for all industries. Whether it be for more efficient operations, or complying to current regulations, the need to build a better mouse trap is always present.

A very promising cost-cutting technology is wireless instrumentation. Wireless provides a compelling argument to change when you consider installation and overall cost effectiveness. Even more so when the application is located in a harsh environment, or where toxic or combustible situations exist. These robust devices provide critical performance data around the clock in the most inhospitable place in the plant, and operate through rain, wind, high temperatures and high humidity.

Untethered by cables and hard-wiring, wireless instrumentation is easier to deploy and monitor. Wireless transmitters are available for monitoring virtual all process variables such as pressure, temperature, level, flow, density, and acoustics. Networks of up to 100 (900 MHz) field devices can be created and then monitored by a single base radio or access point, with a typical communication range of over 1/2 mile. By communicating through the industry standard, Modbus, compatibility between device manufacturers is ensured.
Wireless Instrumentation
Wireless Instrumentation (Accutech and Foxboro)

The most obvious reason for choosing wireless over hard-wiring is the cost savings associated with running wires and cables. Savings estimates as high as 70% can be realized by deploying wireless field devices, compared to the same application using cables. Additional savings are realized when you consider that these devices use batteries and that the cost of adding to a network is borne only by the cost of the new device.

Wireless instruments also provide significant benefits in safety and compliance by keeping personnel out of hazardous areas. Areas that would require occasional human visitation can be safely monitored through remote monitoring.

So, what's the hold up? If the benefits are so clear, and the argument is so strong, why is there still reluctance to embrace wireless technology?

There are three main concerns:

Reliability
Wireless instrumentation must provide the same reliability (real and perceived) as traditional wired units. Every engineer, operator and maintenance person knows wires. Troubleshooting wires is easy, and understanding the failures of wires is basic - the wire is either cut or shorted. With wireless however, air is the communication medium and radio signals replace wires. Radio signals are more complicated than wires in terms of potential problems. For instance, signal strength, signal reflection and interference are all possible impediments to reliable links.

The good news is that radio frequency design is continuously improving, and the use of new and advanced technologies, such as frequency hopping receivers and high gain antennas, are enabling wireless devices to create highly reliable links.

Adapting to Existing Infrastructure
Wireless instrumentation networks have to adapt to the existing environment and the placement of structures and equipment. Most times it's just not practical to relocate equipment just to create a reliable wireless link. This can make it challenging to find the optimum location for a base radio or access point that is capable of providing a reliable communication link to your wireless instruments. Furthermore, accommodating the best strategy for one wireless device could negatively affect links with other devices on the same network.

The challenges of adaptability are being overcome by providing better frequency bands (such as 900 MHz). These bands provide longer range, the ability to pass through walls, and offer more saturating coverage. Other ways to overcome adaptability concerns are through the use of external, high gain antennas mounted as physically high as possible, and also by using base radios with improved receiving sensitivity.

Integration with Existing Communications
Engineers, operators, and maintenance crews are challenged by integrating wireless instrumentation networks with other, existing, field communications systems. The issues of having to manage and troubleshoot multiple networks adds levels of complexity to existing systems. This creates a conflict between the financial argument to adopt wireless instrumentation and the possible costs to increase the data gathering capabilities of an existing system. For instance, SCADA systems need to be able to handle the additional data input from wireless devices, but may not have the capacity. Adding the additional data capacity to the SCADA system can be expensive,  and therefore offset the wiring and cabling savings.

The financial argument for industry to adopt wireless instrumentation networks is persuasive, but its acceptance in the process control industry is slow. Reliability, acclimation, and integration are all challenges that must be overcome before widespread adoption occurs. Eventually though, the reality of dramatically reduced deployment and maintenance costs, increased safety, and improved environmental compliance will tip the scale and drive wireless as the standard deployment method.

Always consult with an experienced applications engineer before specifying or installing wireless instrumentation. Their experience and knowledge will save you time, cost, and provide another level of safety and security.

Thursday, April 12, 2018

Mead O'Brien: Problem Solver, Innovator, and Best Total Cost Provider

Mead O’Brien specializes in valves & valve automation, steam & hot water products and systems, instrumentation products, skid designs, field services, surveys, assessments, and consulting. The extensive product and application knowledge possessed by the Mead O'Brien sales force projects to all or part of ten states in the Midwest which includes Missouri, Kansas, Nebraska, Iowa, Oklahoma, Arkansas, Texas Panhandle, Southern Illinois, Western Kentucky, and Southwest Indiana.

Saturday, March 31, 2018

How Your Steam Trap Selection Affects Your Bottom Line Profits: Inverted Bucket Trap vs.Thermodynamic Trap

Steam Trap Selection
Below is a white paper, courtesy of Armstrong International, describing how steam trap selection affects profitability. This document compares Inverted Bucket Traps and Thermodynamic Traps.

The ability to monitor and maintain your facility’s steam trap population directly affects your bottom line. Armstrong’s Steam Testing and Monitoring Systems give you the means to achieve best practice steam system management by proactively monitoring your steam trap inventory.

For more information on Armstrong steam and hot water products, visit Mead O'Brien at https://meadobrien.com of call (800) 892-2769.


Monday, March 26, 2018

Process Instrumentation and Noise

Protect instrumentation from electrical noise.
Protect process instrumentation from
electrical noise.
Instrument noise, and eliminating instrument noise, is important to consider in process control instrumentation. Noise represents variations in process variable measurement that is not reflective of actual changes occurring in the process variable. Typically, electrical devices such as high voltage wiring, electric motors, relays, contactors, and radio transmitters are the primary sources of instrument noise.

No matter the cause for the process noise, the measurement signal in the process is being distorted and is not reflecting the true state of the process at a certain time. Accuracy and precision of process measurements are negatively affected by noise, and can also contribute to errors in control system. Controller output can reflect the noise affecting a process variable.

Grounding allows for the reduction of noise stemming from electrical systems. Shielded cabling and separating signal cabling from other wiring, as well as replacing and repairing sensors, allows for noise reduction. Low-pass filters are a way to compensate for noise, and much of the instrumentation used in process systems incorporates noise dampening features automatically. Determining the best kind of filter to use depends heavily on cut-off frequency, alpha value, or time constant.

The ideal low-pass filter would eliminate all frequencies above the cutoff frequency while allowing every frequency below the cut-off frequency to be unaffected. However, this ideal filter is only achievable mathematically, while real applications must approximate the ideal filter. They calculate a finite impulse response, and also must delay the signal for a bit of time. To achieve better filter accuracy, a longer delay is needed so that the filter computation “sees” a bit further into the future. The calibration of these filters heavily relies on the desired accuracy level of the process, while also taking specific steps in calibration to best fit a particular process.

Noise is important to mitigate because the noise observed while measuring the process variable can produce “chatter” in the final control element of a process. The resulting “chatter” increases the wear of mechanical control elements, such as valves, and will generate additional cost for the process as a whole. The filtered signal lagging behind the dynamic response of the unfiltered signal is a result of the filtered signal’s increased dead time, meaning that signal filters add a delay in sensing the true process state. The solution is to find a mid-point between signal smoothing and information delay, which allows for elimination of noise while not negatively affecting the speed by which information is delivered.

For question about any process control application, or challenge, visit https://meadobrien.com or call (800) 892-2769

Saturday, March 17, 2018

What Are Isolation Rings?

Isolation Rings
Isolation Rings (Ashcroft)
Isolation Rings are used for protection of sensitive and expensive pressure instrumentation, such as pressure switches, transmitters, and transducers. They isolate the instrument from an aggressive or viscous process. The Isolation Ring is mounted inline with process piping and fits between the process line pipe flanges, similar to wafer butterfly valves.

The ring design includes ring has a  flexible inner cylinder that prevents process media from collecting in the instrument, and therefore assuring reliable and continuous pressure measurement. An integrated needle valve allows for fast and easy removal for instrument repair, replacement, or calibration without interrupting the process media flow. The needle valve can also be used for pulsation dampening.

Watch the video below for a more in-depth understanding of how Isolation Rings are installed and operate.

For more information, contact Mead O'Brien by calling (800) 892-2769 or visiting https://meadobrien.com.

Tuesday, February 27, 2018

Commissioning a Glass Level Gauge with a Safety Ballcheck Valve

Safety ballcheck valves are intended to safely isolate boiler and tank level gauges from the process media. Jerguson, a premier manufacturer of safety ballcheck valves and liquid level gauges has put together this video to explain how to commission a glass level gauge with a safety ballcheck valve.

https://meadobrien.com
(800) 892-2769


Tuesday, February 20, 2018

Steam Trapping and Steam Tracing Equipment

Inverted Bucket Steam Trap
Inverted Bucket Steam Trap
(Armstrong)
An efficient steam trap wastes less energy, which means you burn less fuel and reduce emissions. The results are energy savings and a cleaner, healthier environment. By helping companies manage energy, Armstrong steam traps are also helping protect the world we all share.

As a steam trap wears, it loses efficiency and begins to waste energy. But Armstrong inverted bucket traps last years longer than other traps. They operate more efficiently longer because the inverted bucket is the most reliable steam trap operating principle known.

Clearly, the longer an efficient trap lasts, the more it reduces energy wasted, fuel burned and pollutants released into the air. It’s an all-around positive situation that lets the environment win, too. Bringing energy down to earth in your facility could begin with a renewed focus on your steam system, especially your steam traps. Said another way: Zeroing in your steam traps is an easy way to pay less money for energy—and more attention to the environment.

Companies around the world are beginning to realize that rather than being separate challenges, energy and the environment are and have always been a single mission. And that quality management in one area will surely impact the other.

The catalog below should be utilized as a guide for the installation and operation of steam trapping equipment. Selection or installation should always be accompanied by competent technical assistance or advice. Armstrong and its local representatives are available for consultation and technical assistance. We encourage you to contact your Armstrong Representative for complete details.

Monday, February 12, 2018

The Orifice Plate: Great for Gases, Clean Liquids, and Low Velocity Steam

Orifice Plate
Orifice plate mounted in flange and alone.
Courtesy of Armstrong International.
An orifice plate, at its simplest, is a plate with a machined hole in it. Carefully control the size and shape of the hole, mount the plate in a fluid flow path, measure the difference in fluid pressure between the two sides of the plate, and you have a simple flow measurement setup. The primary flow element is the differential pressure across the orifice. It is the measurement from which flow rate is inferred. The differential pressure is proportional to the square of the flow rate.

Orifice plates are the most commonly used differential pressure measurement device and are applicable for measurements in gases, clean liquids, and low velocity steam.  Orifice plates allow for relatively easy installation and replacement if necessitated by changes in process parameters or life cycle deterioration.

An orifice plate is often mounted in a customized holder or flange union that allows removal and inspection of the plate. A holding device also facilitates replacement of a worn orifice plate or insertion of one with a different size orifice to accommodate a change in the process. While the device appears simple, much care is applied to the design and manufacture of orifice plates. The flow data obtained using an orifice plate and differential pressure depend upon well recognized characteristics of the machined opening, plate thickness, and more. With the pressure drop characteristics of the orifice fixed and known, the measuring precision for differential pressure becomes a determining factor in the accuracy of the flow measurement.
Orifice plate configurations
Orifice plate configurations (click for larger view).
There are standards for the dimensional precision of orifice plates that address:
  • Circularity of the bore
  • Flatness
  • Parallelism of the faces
  • Edge sharpness
  • Surface condition
Orifice plates can be effectively "reshaped" by corrosion or by material deposits that may accumulate from the measured fluid. Any distortion of the plate surface or opening has the potential to induce measurable error. This being the case, flow measurement using an orifice plate is best applied with clean fluids.

Certain aspects of the mounting of the orifice plate may also have an impact on its adherence to the calibrated data for the device. Upstream and downstream pipe sections, concentric location of the orifice in the pipe, and location of the pressure measurement taps must be considered.
orifice plate
Orifice plate between two flanges.
Properly done, an orifice plate and differential pressure flow measurement setup provides accurate and stable performance. Share your flow measurement challenges of all types with a specialist, combining your own process knowledge and experience with their product application expertise to develop an effective solution.

Download a cut sheet for Armstrong orifice plates and flanges from this Mead O'Brien link.

For more information, call (800) 892-2769 or visit https://meadobrien.com.

Wednesday, January 31, 2018

Industrial Valve Actuators

Valve actuators are selected based upon a number of factors including torque necessary to operate the valve and the need for automatic actuation. Types of actuators include manual handwheel, manual lever, electrical motor, pneumatic, and solenoid. All actuators except manual handwheel and lever are adaptable to automatic actuation.

Handwheel
Handwheel (Metso)
Manual Actuators

Manual actuators are capable of placing the valve in any position but do not permit automatic operation. The most common type mechanical actuator is the handwheel. This type includes handwheels fixed to the stem and handwheels connected to the stem through gears.

Electric Motor Actuators

Electric Actuator
Electric Actuator (Limitorque)
Electric motors permit manual, semi-automatic, and automatic operation of the valve. Motors are used mostly for open-close functions, although they are adaptable to positioning the valve to any point opening. The motor is usually a, reversible, high speed type connected through a gear train to reduce the motor speed and thereby increase the torque at the stem. Direction of motor rotation determines direction of disk motion. The electrical actuation can be semi-automatic, as when the motor is started by a control system. A handwheel, which can be engaged to the gear train, provides for manual operating of the valve. Limit switches are normally provided to stop the motor automatically at full open and full closed valve positions. Limit switches are operated either physically by position of the valve or torsionally by torque of the motor.

Pneumatic Actuators

Pneumatic Actuator
Pneumatic Actuator
(Metso Neles)
Pneumatic actuators provide for automatic or semi-automatic valve operation. These actuators translate an air signal into valve stem motion by air pressure acting on a vane, diaphragm, or piston connected to the stem. Pneumatic actuators are used in throttle valves for open-close positioning where fast action is required. When air pressure closes the valve and spring action opens the valve, the actuator is termed direct-acting. When air pressure opens the valve and spring action closes the valve, the actuator is termed reverse-acting. Double acting actuators have air supplied to both sides of the vane, diaphragm, or piston. The differential pressure across the diaphragm positions the valve stem. Automatic operation is provided when the air signals are automatically  controlled by circuitry. Semi-automatic operation is provided by manual switches in the circuitry to the air control valves.


Hydraulic Actuators

Hydraulic actuators provide for semi-automatic or automatic positioning of the valve, similar to the pneumatic actuators. These actuators use a piston to convert a signal pressure into valve stem motion. Hydraulic fluid is fed to either side of the piston while the other side is drained or bled. Water or oil is used as the hydraulic fluid. Solenoid valves are typically used for automatic control of the hydraulic fluid to direct either opening or closing of the valve. Manual valves can also be used for controlling the hydraulic fluid; thus providing semi-automatic operation.

Solenoid Actuated Valves

Solenoid Valve
Solenoid Valve (ASCO)
Solenoid actuated valves provide for automatic open-close valve positioning. Most solenoid actuated valves also have a manual override that permits manual positioning of the valve for as long as the override is manually positioned. Solenoids position the valve by attracting a magnetic slug attached to the valve stem. In single solenoid valves, spring pressure acts against the motion of the slug when power is applied to the solenoid. These valves can be arranged such that power to the solenoid either opens or closes the valve. When power to the solenoid is removed, the spring returns the valve to the opposite position. Two solenoids can be used to provide for both opening and closing by applying power to the appropriate solenoid.

Single solenoid valves are termed fail open or fail closed depending on the position of the valve with the solenoid de-energized. Fail open solenoid valves are opened by spring pressure and closed by energizing the solenoid. Fail closed solenoid valves are closed by spring pressure and opened by energizing the solenoid. Double solenoid valves typically fail "as is." That is, the valve position does not change when both solenoids are de-energized.

One application of solenoid valves is in air systems such as those used to supply air to pneumatic valve actuators. The solenoid valves are used to control the air supply to the pneumatic actuator and thus the position of the pneumatic actuated valve.

Mead O'Brien can handle any valve actuation requirement you have. Contact them by calling (800) 892-2769 or by visiting https://meadobrien.com.

Tuesday, January 30, 2018

Steam Boiler Water Level Control

Steam boiler level control diagram.
Steam boiler level control diagram.
Click on image for larger view.
Steam boilers are very common in industry, principally because steam power is so useful. Common uses for steam in industry include doing mechanical work (e.g. a steam engine moving some sort of machine), heating, producing vacuums (through the use of “steam ejectors”), and augmenting chemical processes (e.g. reforming of natural gas into hydrogen and carbon dioxide).

The process of converting water into steam is quite simple: heat up the water until it boils. Anyone who has ever boiled a pot of water for cooking knows how this process works. Making steam continuously, however, is a little more complicated. An important variable to measure and control in a continuous boiler is the level of water in the “steam drum” (the upper vessel in a water-tube boiler). In order to safely and efficiently produce a continuous flow of steam, we must ensure the steam drum never runs too low on water, or too high. If there is not enough water in the drum, the water tubes may run dry and burn through from the heat of the fire. If there is too much water in the drum, liquid water may be carried along with the flow of steam, causing problems downstream.

The first instrument in this control system is the level transmitter, or “LT”. The purpose of this device is to sense the water level in the steam drum and report (“transmit”) that measurement to the controller in the form of a signal. In this case, the type of signal is pneumatic: a variable air pressure sent through metal or plastic tubes. The greater the water level in the drum, the more air pressure output by the level transmitter. Since the transmitter is pneumatic, it must be supplied with a source of clean, compressed air on which to operate. This is the meaning of the “A.S.” tube (Air Supply) entering the top of the transmitter.

This pneumatic signal is sent to the next instrument in the control system, the level indicating controller, or “LIC”. The purpose of this instrument is to compare the level transmitter’s signal against a setpoint value entered by a human operator representing the desired water level in the steam drum. The controller then generates an output signal telling the control valve to either introduce more or less water into the boiler to maintain the steam drum water level at setpoint. As with the transmitter, the controller in this system is pneumatic, operating entirely on compressed air. This means the output of the controller is also a variable air pressure signal, just like the signal output by the level transmitter. Naturally, the controller requires a constant supply of clean, compressed air on which to run, which explains the “A.S.” (Air Supply) tube connecting to it.

The last instrument in this control system is the control valve, operated directly by the air pressure signal output by the controller. Its purpose is to influence the flow rate of water into the boiler, “throttling” the water flow more or less as determined by controller. This particular type of control valve uses a large diaphragm and a large spring to move the valve further open with more signal pressure and further closed with less signal pressure.

When the controller is placed in the “automatic” mode, it will move the control valve to whatever position necessary to maintain a constant steam drum water level. The phrase “whatever position necessary” suggests the relationship between the controller output signal, the process variable signal (PV), and the setpoint (SP) is complex. If the controller senses a water level above setpoint, it will close off the valve as far as necessary to decrease the water level down to setpoint. Conversely, if the controller senses a water level below setpoint, it will open up the valve as far as necessary to raise the water level up to setpoint.

What this means in a practical sense is that the controller’s output signal (equating to valve position) in automatic mode is just as much a function of process load (i.e. how much steam is being used from the boiler) as it is a function of setpoint (i.e. where we wish the water level to be). Consider a situation where the steam demand from the boiler is very low. If there isn’t much steam being drawn off the boiler, this means there will be little water boiled into steam and therefore little need for additional feedwater to be pumped into the boiler. Therefore, in this situation, one would expect the control valve to hover near the fully-closed position, allowing just enough water into the boiler to keep the steam drum water level at setpoint. If, however, there is a high demand for steam from this boiler, the rate of evaporation will be much greater. This means the control system must add feedwater to the boiler at a much greater flow rate in order to maintain the steam drum water level at setpoint. In this situation we would expect to see the control valve much closer to being fully-open as the control system “works harder” to maintain a constant water level in the steam drum. Thus, we see how the controller automatically positions the control valve to react to different boiler operating conditions even when the setpoint is fixed.

A human operator supervising this boiler has the option of placing the controller into “manual” mode. In this mode the control valve position is under direct control of the human operator, with the controller essentially ignoring the signal sent from the water level transmitter. Being an indicating controller, the controller faceplate will still show how much water is in the steam drum, but it is now the human operator’s sole responsibility to move the control valve to the appropriate position to hold water level at setpoint – in manual mode the controller takes no corrective action of its own. Manual mode is useful to human operators during start-up and shut-down conditions. It is also useful to instrument technicians for troubleshooting misbehaving control systems. Placing a controller into manual mode is akin to disengaging the cruise control in an automobile, transferring control of engine power from the car’s computer back to the human driver. One can easily imagine an automobile mechanic needing to throttle a car’s engine “manually” (i.e. with the cruise control turned off) in order to properly diagnose an engine or drivetrain problem. This is true for industrial processes as well, where instrument technicians may need to place a controller into manual mode in order to properly diagnose transmitter or control valve problems.

Reprinted from Lessons In Industrial Instrumentation by Tony R. Kuphaldt – under the terms and conditions of the Creative Commons Attribution 4.0 International Public License.

Wednesday, January 24, 2018

Two Point Calibration of the Foxboro IDP-10-T Pressure Transmitter

The Foxboro / Schneider Electric I/A Series Electronic Pressure Transmitters are a complete family of D/P Cell, gauge, absolute, multirange, multivariable, and premium performance transmitters, as well as transmitters with remote or direct connect seals, all using field-proven silicon strain gauge sensors and common topworks.

A common HART electronics module is used for all HART Pressure Transmitters. Also, because all configuration and calibration data is stored in the sensor, you can replace a HART module with another HART module without transmitter reconfiguration or recalibration.

The video below provides step-by-step instructions for two point calibration of the IDP-10-T pressure transmitter.

Tuesday, January 16, 2018

Flowserve Limitorque WG Series Gear Operator Installation, Maintenance, and Operation Guide

WG Series Gear Operator
WG Series Gear Operator (Limitorque)
The most basic function of a valve is to be opened and closed, allowing or preventing a process media to flow. Gearboxes, such as the WG series, provide the mechanical advantage to make hand operation possible for most valves.

The Flowserve Limitorque WG series of worm gearboxes is designed for quarter-turn butterfly, ball, and plug valve applications as well as quarter-turn and multi-turn dampers and offers unsurpassed quality and longevity in a wide variety of weatherproof, submersible and buried-service applications.

The following installation and maintenance manual (IOM) explains how to install and maintain the Flowserve Limitorque WG operator. Information on installation, disassembly, reassembly, lubrication and spare parts is provided in the embedded document below.

Alternatively, you can conveniently download the Limitorque WG Series Installation, Operation, and Maintenance in PDF here.