Process Flow and Process Instrument Diagrams

To show a practical process example, let’s examine three diagrams for a compressor control system, beginning with a Process Flow Diagram, or PFD. In this fictitious process, water is being evaporated from a process solution under partial vacuum (provided by the compressor). The compressor then transports the vapors to a “knockout drum” where they condense into liquid form. As a typical PFD, this diagram shows the major interconnections of process vessels and equipment, but omits details such as instrument signal lines and auxiliary instruments:

One might guess the instrument interconnections based on the instruments’ labels. For instance, a good guess would be that the level transmitter (LT) on the bottom of the knockout drum might send the signal that eventually controls the level valve (LV) on the bottom of that same vessel. One might also guess that the temperature transmitter (TT) on the top of the evaporator might be part of the temperature control system that lets steam into the heating jacket of that vessel.

Based on this diagram alone, one would be hard-pressed to determine what control system, if any, controls the compressor itself. All the PFD shows relating directly to the compressor is a flow transmitter (FT) on the suction line. This level of uncertainty is perfectly acceptable for a PFD, because its purpose is merely to show the general flow of the process itself, and only a bare minimum of control instrumentation.

Process and Instrument Diagrams

The next level of detail is the Process and Instrument Diagram, or P&ID. Here, we see a “zooming in” of scope from the whole evaporator process to the compressor as a unit. The evaporator and knockout vessels almost fade into the background, with their associated instruments absent from view:

Now we see there is more instrumentation associated with the compressor than just a flow transmitter. There is also a differential pressure transmitter (PDT), a flow indicating controller (FIC), and a “recycle” control valve allowing some of the vapor coming out of the compressor’s discharge line to go back around into the compressor’s suction line. Additionally, we have a pair of temperature transmitters reporting suction and discharge line temperatures to an indicating recorder.

Some other noteworthy details emerge in the P&ID as well. We see that the flow transmitter, flow controller, pressure transmitter, and flow valve all bear a common number: 42. This common “loop number” indicates these four instruments are all part of the same control system. An instrument with any other loop number is part of a different control system, measuring and/or controlling some other function in the process. Examples of this include the two temperature transmitters and their respective recorders, bearing the loop numbers 41 and 43.

lease note the differences in the instrument “bubbles” as shown on this P&ID. Some of the bubbles are just open circles, where others have lines going through the middle. Each of these symbols has meaning according to the ISA (Instrumentation, Systems, and Automation society) standard:

The type of “bubble” used for each instrument tells us something about its location. This, obviously, is quite important when working in a facility with many thousands of instruments scattered over acres of facility area, structures, and buildings.

The rectangular box enclosing both temperature recorders shows they are part of the same physical instrument. In other words, this indicates there is really only one temperature recorder instrument, and that it plots both suction and discharge temperatures (most likely on the same trend graph). This suggests that each bubble may not necessarily represent a discrete, physical instrument, but rather an instrument function that may reside in a multi-function device.

Details we do not see on this P&ID include cable types, wire numbers, terminal blocks, junction boxes, instrument calibration ranges, failure modes, power sources, and the like. To examine this level of detail, we must turn to another document called a loop diagram (not in this post).

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.

Drexelbrook’s ThePoint™ Series Point Level Switch: Settings, Adjustments, and Changing Calibration Modes

The AMETEK Drexelbrook ThePoint™ Series uses No-Cal™ technology to detect the presence or absence of material without calibration or initiation via setpoint adjustments, push-buttons or magnets.

ThePoint™ level measurement switch features both Auto-Cal and manual calibration. The standard Auto-Calibration mode is applicable to most liquid and slurry point level measurements. If preferred, the manual calibration can be used and is recommended for some application. ThePoint electronic unit has auto and manual calibration modes built into the standard unit and can be accessed through the simple routine shown in the video below. The inclusion of these calibration modes allows the Drexelbrook RF Point Level Products application flexibility that is far greater than any other point level product on the market. ThePoint™ level switch can be used in Liquids, Solids, Slurries, and Interface applications.

To learn more specific instructions on the (8) calibration modes ThePoint™ has available, download the "Drexelbrook ThePoint Series Point Level Switch Installation and Operating Instructions" from this link.

Piping Specialties / PSI Controls: New England's Preferred Source for Industrial Valves, Valve Automation, and Process Instrumentation

Founded in 1975, with offices in Portland, Maine and Danvers, Massachusetts, PSI has earned their reputation as New England's premier supplier of industrial valves, valve automation, process instrumentation and specialty process equipment.

PSI specializes in engineered products for these industries:

• Power Generation
• Pulp & Paper
• LNG / LPG / Natural Gas / Gas Storage & Distribution
• Pharmaceutical / BioTech
• Food and Beverage
• HVAC
• Water & Wastewater

Piping Specialties, Inc / PSI Controls
https://psi-team.com
800-223-1468

Top 5 Considerations in Selecting Pressure Gauges

Pressure gauges are ubiquitous in industry and installed on machinery around the world. While there are millions of possible combinations of shapes, sizes, options and materials, careful attention needs to be given to the following five criteria for safe use and long product life.

1) Process Media
Direct exposure of the sensing element to the process media is a possibility, so attention must be given to any corrosive media, media with particulate, or media that can solidify and clog the pressure gauge element. For non-clogging media, a direct connection and Bourdon tube sensor can be applied. For process media that could potentially cause clogging, a diaphragm seal should be used.

2) Process Media Temperature

Gauge with
diaphragm seal.
(AMETEKUS Gauge)

Very hot media, such as steam or hot water, can elevate the gauge's internal temperature leading to failure or an unsafe condition. For high temperature application, the use of a gauge "siphon" or diaphragm seal be applied.

3) Ambient Operating Temperature and Environment
It is important to know the rated ambient environment for any instrument. Elevated ambient temperatures, moisture, vibration, and corrosive atmospheres can all affect accuracy, calibration, and safety. Choose the proper case and mechanism materials if oxidizing or reducing atmospheres exist, and consider the addition of ancillary devices, such as remote diaphragm seals, to relocate the gauge.

4) Possibility of Severe Pressure Fluctuations

In applications where dramatic line pulsations or strong over-pressure conditions are a possibility the use of pressure restrictors, snubbers, or liquid-filling will extend the service life of the pressure gauge.

5) Mounting

Snubbers & restrictors

Pressure gauges are standardly available with bottom (radial) and back connections. NPT (National Pipe Thread Taper) threaded connections are generally the standard. Many other process connections are available though, such as straight threads, metric threads, and specialized fittings. Make sure you know how the gauge is being connected. When mounting, pressure gauges should be almost always be mounted upright.

For more information about pressure gauges, contact PSI Controls by visiting https://psi-team.com or by calling 800-223-1468.

What is an External Spring, Lever & Weight Single Disc Check Valve

Single disk check valve animation.

According to Wikipedia, "Check valves are used in many fluid systems such as those in chemical and power plants, and in many other industrial processes."

Check valve symbol

As shown in the animation to the left, the single disc (swing) check valve use the directional flow to push open a swinging disk. As long as flow continues, the disk stays raised. But as flow stops, gravity allows the disk to re-seat itself and any reverse flow is prevented by the closed disk. As reverse flow pressure increases, the swing check valves seating increases as well.

Single disc check valves also use springs, levers and/or weights mounted on the valve to allow for better control of surge and to prevent the valve from slamming closed. These assemblies are used to vary the valve’s closing operation in order to reduce the severity of the closing water hammer.

External spring, external spring & lever, and external spring, level & weight designs (left to right).
Courtesy of Champion Valve.

For more information on any industrial check valve, contact Piping Specialties, Inc. by visiting https://psi-team.com or calling 800-223-1468.

An Introduction to Triple Offset Butterfly Valves

Triple Offset Butterfly Valve
(Pratt Industrial)

Triple offset butterfly valves are designed to fill the demand for an alternate solution to gate valves and ball valves. They are preferred when weight, space, performance, and the ability to modulate to the process flow are an issue. Typically available in sizes 3" through 48", and in 150, 300 and 600 pressure classes, they're rated for operation from -50 deg. F. through 750 deg. F.

Designed with metal-to metal seats, triple offset butterfly valves provide distinct advantages over traditional gate valves, namely lower weight, zero-leakage, ease in automation, and capable of being used for modulating service.

Industries Using 

• Chemical
• Refinery
• Power
• Steam Generation
• Petrochemical
• Water/Waste Water Treatment

Click on image for larger view.

Triple Eccentric Disc-Shaft Design (diagram above)

• Offset 1: It is accomplished by moving the centerline of the shaft away from the seating plane.
• Offset 2: It is accomplished by moving the centerline of the shaft offset from the centerline bore of the valve.
• These two design features cause the disc to open and close relative to the body seat in a “camming” action and effectuate the position seated valve design which is typical of the High Performance Butterfly Valve, however there is still contact between the disc and the seat in the first several degrees of opening and closing which can cause premature wear of the seat in the general areas.
• In order to achieve an API 598 Shut Off classification a 3rd offset needed to be introduced to make the valve a “torque seated” design with graphite and metal seating surfaces.
• Offset 3: It is accomplished by adjusting the cone angle created by the 1st and 2nd offset angles at some point downstream of the valve in the center of the piping to the adjacent piping wall as depicted in the illustration below “Sticking tendency”. By incorporating the 3 offsets into one design typical of gate valves is eliminated with seat contact throughout the entire stroke reducing run torques and improving actuator modulating performance at the same time.

For more information, contact Piping Specialties by visiting https://psi-team.com or by calling 800-223-1468.

What is a Piping and Instrumentation Diagram (P&ID)?

Piping and  instrumentation diagrams (P&ID's) are schematic representations of a process control system and used to illustrate the piping system, process flow, installed equipment, and process instrumentation and functional relationships therein. They are also known as "process and control flow diagrams".

They are intended to provide a “picture” of all the process piping, including the physical branches, valves, equipment, instrumentation and interlocks. By using a standard set of internationally recognized symbols, each component of the process system - instruments, piping, motors, pumps - is recognized on paper or computer screen.

P&ID’s may be very detailed and are generally the primary source from where instrument and equipment lists are generated. They are also used as a handy reference for maintenance planning and system upgrades. Furthermore, P&ID’s also play an important early role in plant safety planning by providing a thorough understanding of the operability and relationships of all components in the system.

Watch the short video below for more information.

For more information contact:
Piping Specialties / PSI
https://psi-team.com
800-223-1468

Continuous and Point Level Control Selection Guide

Drexelbrook Continuous and Point Level Control Products

Based on experience from of thousands of inquiries about level measurement, most questions boil down to "What is the best level measurement instrument for my application? That depends on quite a few application considerations, such as:

• Will the measured media add coating to the probe?
• Can the probe have contact with the media?
• Are there explosion hazards?
• What is the physical type of application, well, tank, open channel or floating roof tank?

This document can help deliver the perfect continuous level transmitter or level switches for your application.

Download a PDF version of the Drexelbrook Continuous and Point Level Control Selection Guide here, or view the embedded document below.

https://psi-team.com
800-223-1468

Drexelbrook Continuous & Point Level Selection Guide from Piping Specialties, Inc and PSI Controls

Considerations for Choosing Industrial Butterfly Valves

High Performance Butterfly Valve
(Pratt)

Industrial process control valves are available in uncountable combinations of materials, types, and configurations. An initial step of the selection procedure for a valve application should be choosing the valve type, thus narrowing the selection field to a more manageable level. Valve "types" can generally be classified by the closing mechanism of the valve.

A butterfly valve has a disc that is positioned in the fluid flow path. In the most common form of butterfly valve, the disc rotates around a central axis, the stem, through a 90 degree arc from a position parallel to the flow direction (open) to perpendicular (closed). A variety of materials are used in the valve body construction, and it is common to line the valve with another material to provide special properties accommodating particular process media.

What attributes might make a butterfly valve a beneficial selection over another valve type?

Resilient Seated Butterfly Valve
(Pratt)

• The closure arrangement allows for a comparatively small size and weight. This can reduce the cost, space, and support requirements for the valve assembly.
• Generally low torque requirements for valve operation allow for manual operation, or automation with an array of electric, pneumatic, or hydraulic actuators.
• Low pressure drop associated with the closure mechanism. The disc in the flow path is generally thin. In the fully open position, the disc presents its narrow edge to the direction of flow.
• Quarter turn operation allows for fast valve operation.
• Some throttling capability is provided at partially open positions.
• Small parts count, low maintenance requirements.

What may be some reasons to consider alternate valve types?

• Butterfly valve throttling capability is generally limited to low pressure drop applications.
• Cavitation can be a concern.
• Some sources mention the possibility of choked flow as a concern under certain conditions.

Butterfly valves, like other valve types, have applications where they outperform. Careful consideration and consultation with a valve expert is a first step toward making a good selection. Combine your process know-how with the product application expertise of a professional sales engineer to produce the best solutions to your process control challenges.

For more information regarding an type of industrial valve, contact Piping Specialties, Inc. by visiting https://psi-team or by calling 800-223-1468.

MOGAS Severe Service Ball Valve "Mate Lap" Seal Demonstration

The video below demonstrates the effectiveness of the MOGAS "Mate Lap" seal provided on MOGAS severe service ball valves.

MOGAS valves have outperformed others worldwide in some of the most severe service conditions, including: Extreme temperatures; High pressures; Abrasive particulates; Acidic products; Heavy solids build-up; Critical plant safety; Large pressure differentials; Velocity control; Noise control.

Best Practices Document for the K-Patents PR-23-SD Safe-Drive™ Process Refractometer

This document is intended for individuals installing, commissioning, operating, and/ or servicing the Safe-DriveTM Process Refractometer PR-23-SD, generation 2.1 model. The purpose of this document is to provide a quick guide for the abovementioned tasks in the form of K-Patents recommended best practices.

This document is intended for PR-23-SD applications that have a steam wash system (typical application for black liquor) and applications that have high pressure water wash system (typical application for green liquor).

NOTE: These instructions are for quick reference only. For more thorough guidance, please refer to the K-Patents user manual and documentation that came with your equipment.

Review the embedded document below, or download a PDF version of Safe-Drive™ Process Refractometer PR-23-SD Generation 2.1 Best Practices here.

Safe-Drive™ Process Refractometer PR-23-SD Generation 2.1 Best Practices from Piping Specialties, Inc and PSI Controls

Operating Principles and Application of Vortex Flowmeters

Animation of vortices*

To an untrained ear, the term "vortex flowmeter" may conjure futuristic, potentially Star Wars inspired images of a hugely advanced machine meant for opening channels in warp-space. In reality, vortex flowmeters are application specific, industrial grade instruments designed to measure an important element of a fluid process control operation: flow rate.

Vortex flowmeters operate based on a scientific principle called the von Karman effect, which generally states that a fluid flow will alternately shed vortices when passing by a solid body. "Vortices" is the plural form of vortex, which is best described as a whirling mass, notably one in which suction forces operate, such as a whirlpool. Detecting the presence of the vortices and determining the frequency of their occurrence is used to provide an indication of fluid velocity. The velocity value can be combined with temperature, pressure, or density information to develop a mass flow calculation. Vortex flowmeters exhibit high reliability, with no moving parts, serving as a useful tool in the measurement of liquid, gas, and steam flow.

Photograph of vortices **

While different fluids present unique challenges when applying flowmeters, steam is considered one of the more difficult to measure due to its pressure, temperature, and potential mixture of liquid and vapor in the same line. Multiple types of steam, including wet steam, saturated steam, and superheated steam, are utilized in process plants and commercial installations, and are often related to power or heat transfer. Several of the currently available flow measurement technologies are not well suited for steam flow applications, leaving vortex flowmeters as something of a keystone in steam flow measurement.

Rangeability, defined as a ratio of maximum to minimum flow, is an important consideration for any measurement instrument, indicating its ability to measure over a range of conditions. Vortex flowmeter instruments generally exhibit wide rangeability, one of the positive aspects of the technology and vortex based instruments.

The advantages of the vortex flowmeter, in addition to the aforementioned rangeability and steam-specific implementation, include available accuracy of 1%, a linear output, and a lack of moving parts. It is necessary for the pipe containing the measured fluid to be completely filled in order to obtain useful measurements.

Vortex flowmeter
(Azbil)

Applications where the technology may face hurdles include flows of slurries or high viscosity liquids. These can prove unsuitable for measurement by the vortex flowmeter because they may not exhibit a suitable degree of the von Karman effect to facilitate accurate measurement. Measurements can be adversely impacted by pulsating flow, where differences in pressure from the relationship between two or more compressors or pumps in a system results in irregular fluid flow.

When properly applied, the vortex flowmeter is a reliable and low maintenance tool for measuring fluid flow. Frequently, vortex flow velocity measurement will be incorporated with the measurement of temperature and pressure in an instrument referred to as a multivariable flowmeter, used to develop a complete measurement set for calculating mass flow.

Whatever your flow measurement challenges, share them with a flow instrument specialist, combining your process knowledge with their product and technology expertise to develop effective solutions.

* Animation of vortex creation credit Cesareo de La Rosa Siqueira via Wikipedia.
** Photograph of vortices credit Jürgen Wagner via Wikipedia.

Providing New England Industry with Process Instrumentation, Valves, and Unsurpassed Service for Over 40 Years

PSI operates under one single mission: To provide specialty valves, instruments, control systems and mechanical products to industrial users throughout the Northeast, and to do so by providing unsurpassed customer service.

Covering the states of Maine, Vermont, Massachusetts, New Hampshire, Rhode Island, and Connecticut through offices located in Portland, Maine and Danvers, Connecticut, PSI is well situated to provide quick delivery, on-site services, and engineering support all through New England.

Piping Specialties, Inc. provides industrial valves, including ball, butterfly, gate, globe, safety relief, and control vales; and mechanical specialties including, steam traps, condensate recovery systems, steam water heaters, site level gauges, jet pumps, expansion joints, and modular pipe seals.

PSI Controls provides automated industrial and commercial valve packages that include quarter-turn and linear valves, pneumatic and electric actuators, limit switches and valve communications; and process instrumentation & controls including level, pressure, temperature and flow  instrumentation.

PSI Services provides installation of valve automation systems, valve repair, instrument repair, instrument calibration, turnkey systems and field support services.

Floating Roof Tank Spill Prevention

Floating Roof Tank Spill Prevention (Drexelbrook)

One of the most difficult and critical applications is measuring the high alarm or potential overfill condition on a floating roof tank containing liquid petroleum products such as crude oil or refined products such as fuel. It normally is comprised of a cylindrical steel tank equipped with an internal or external floating roof, that floats on the surface of the stored liquid. Floating roof tank systems are especially beneficial in eliminating the evaporative losses of the liquids. As opposed to a fixed roof tank there is no vapor space in the tank. This helps to reduce risk in highly explosive vapor environments. This is an extremely high cost of failure application, and one in which only the safest and most trusted products are accepted.

Drexelbrook's
Intellipoint

Safe operation of the tank farm relies on critical real time continuous level measurements of the liquids in the tank, as well as detecting when a high level condition exists. Products used in this application are typically required to meet the API 2350 Overfill Protection Standards, as well as SIL Safety Integrity Level performance standards to IEC 61508.

The challenges to reliably detect a high level condition on a floating roof tank are long sensor length requirements, and the variability of what is being measured. The floating roof may be dry in which case you need to detect the position of the physical metal roof. Or there may be a few inches of rain water or petroleum liquids on the roof. Measuring instruments need to determine very accurately, usually within a few millimeters, when the position of the floating roof has reached a high level alarm condition.

Drexelbrook's Intellipoint, with its unique floating roof probe, can accurately detect and alarm on the position of the floating roof or the presence of liquid under all these conditions. The safety Intellipoint is a SIL2 fully certified RF admittance point level switch with uncompromising reliability for the most demanding applications.  Drexelbrook has almost 60 years of RF admittance technology experience and is proud to offer this specialized product as the latest in its award-winning portfolio for the level market.

Product features include:

• Adjustable up to 15 feet, or 4.6 meters, to accurately control the alarm point. 
• A trip point accuracy of a few millimeters.
• Fully SIL2 certified to IEC61508. 
• Worldwide hazardous area approvals .
• Meets overfill protection standards API2350.
• A floating roof tank probe that is unique in the industry.

Refractometer Application for Wet Spinning of Alginate Fibers

Refractometer used for
wet spinning of alginate fiber.
(K-Patents) 

Alginates are biopolymers extracted from brown algae species such as seaweed. Extraction is performed from the harvested material by treatment with aqueous alkaline solutions. The extract is then filtered and the alginate salt is precipitated by the addition of calcium chloride or an acid. After purification, drying and milling, a water-soluble sodium alginate powder is produced. Alginates have found a variety of uses in different industries because of their unique properties. These materials have been extensively used in pharmaceutical applications as they are gel forming, non-toxic and highly absorbent.

The document below illustrates the use of industrial refractometers in the processing of Sodium Alginate. You can also download the full PDF of "Wet Spinning of Alginate Fibers" here.

Refractometer Application for Wet Spinning of Alginate Fibers from Piping Specialties, Inc and PSI Controls

Conval Clampseal Valve Seat Reassembly Instructions

Valve seat reassembly instructions for Conval Clampseal valve.

Conval Clampseal® Valves are much easier to renew than anything else on the market. This video is seventh and final video in a series demonstrating how to service Clampseal valves.

https://psi-team.com
800-223-1468

What is a Magnetic Level Gauge?

Magnetic Level Gauge (Penberthy)

Magnetic level gauges, also known as magnetic level indicators, are routinely used to provide a display of liquid level in tanks and other vessels. Their popularity stems from their high visibility from distances and non-invasive design which reduces the possibility of points and the risks of fugitive emissions.

"Mag Gauge" construction is fairly simple. A magnetic float, designed for the specific gravity of the material being measured, rides inside a vertical pipe on top of the process media. A gauge with magnetically coupled visual indicator is fastened to the pipe. As the media inside the pipe rises and falls, the visual indicator moves in the same fashion.

Magnetic level gauges are often employed in tandem with magnetostrictive, guided wave radar, or other measurement means to provide a reliable local display of liquid level, as well as an electrical signal that can be transmitted to recording instrumentation or controllers.

Magnetic level gauges features:

• Continuous level measurement
• Operable without electric power
• Direct visual tank fluid level indication, regardless of tank shape or profile.
• Wide range of operating temperature and pressure
• Breakage resistant construction
• Range of construction materials available to accommodate corrosive media
• Measuring indicators, switches, and transmitters mounted externally, without contacting the medium being measured.
• Low maintenance operation.
• Readable level indication from greater distance than glass sight gauges.
• Applicable to large fluid level ranges with a single instrument.

Magnetic level indicators are used widely in liquid level measurement and should be considered as a candidate for fulfilling those applications where the magnetic level gauge features fulfill the project requirements. There are many options available to customize the level indicator for each specific application. Share your application challenges with a product specialist, combining your process knowledge with their product application expertise to develop an effective solution.

Piping Specialties and PSI Controls

Piping Specialties was founded in 1975 with the mission of providing specialty valves and mechanical products and unsurpassed customer service to industrial users throughout the Northeast. Over the years our company has experienced steady, sustainable growth in both our customer base and product offerings. With offices in Danvers, MA and Portland, ME, we are geographically well-positioned to serve all of the Northeast.

PSI delivers our products and services through our 3 operating divisions:

• Piping Specialties: valves and mechanical specialties.
• PSI Controls: automated valves and process instrumentation & controls.
• PSI Services: valve automation, valve and instrument repair, calibration, and turnkey installation and field services.

Conval Clampseal Valve Seat Blueing/Lapping Instructions

Conval Clampseal^® Valves are much easier to renew than anything else on the market. This video is sixth in a series demonstrating how to service Clampseal valves.

https://psi-team.com
800-223-1468

Conval Clampseal Valve Seat Refacing/Resurfacing Instructions

Valve Seat Refacing/Resurfacing instructions for Conval Clampseal valve.

Conval Clampseal® Valves are much easier to renew than anything else on the market. This video is fifth in a series demonstrating how to service Clampseal valves.

https://psi-team.com
800-223-1468