Saturday, June 9, 2018

Maryland, Washington D.C., and Virginia's Premier Process, Control, Test & Measurement Representative

Process, Control, Test & Measurement Representative

Flow-Tech, Inc.

Providing applications expertise and engineering support for Power and Chemical plants, OEM’s,
System Integrators, Municipalities, Engineering Firms, Universities, Medical Centers, and Research / Metrology Labs.

Specializing in:

Process Instrumentation

Flow, Data Acquisition & Control Instruments, Gas Detection, Analyzers, Level Control & Measurement, Pressure & Temperature Indicators and Transmitters, Vibration - Asset Condition Monitoring , Indicators & Energy Flow Computers

Pressure Relief, Tank Blanketing and Flame Arrest

Rupture Discs, Tank Conservation Vents, Explosion Venting, Tank Blanketing, Flame Arrestors

Gas Detection

Personal Gas Detection - Portables and Drager Tubes, Hazardous Gas Area Monitor, Respiratory Protection

Control Valves, On-Off Valves and Regulators

Gas, Steam & Liquid Control Valves, Pressure Reducing & Back Pressure Regulators, Sanitary Regulators and Control Valves, On-Off Valves

Explosion Protection Testing, Isolation Valves, Vents and Systems

Active Explosion Suppression Systems, Explosion Isolation Valves, Explosion Venting, Explosion Testing Services

ABB Low & Medium Voltage VFD Drives

ABB General Purpose Drives, ABB Industrial AC Drives, ABB Industry Specific Drives

Environmental Instruments

Flow, Gas Detection, Analyzers, Pressure & Temperature Indicators and Transmitters, Indicators, Mosaic Displays and Annunciators, Paperless Recorders & Data Acquisition

Saturday, May 26, 2018

Yokogawa EJA-E or EJX-A Series Pressure Transmitter LPS (Local Parameter Setting) Overview

Yokogawa EJA-E
Yokogawa EJA-E
We have all run into this problem one time or another; you're out in the process area when you realized you need to make a change to a transmitter, but your Hand Held Communicator (HHC) is back at the instrument shop! Your HHC is a great device, but it does you no good when it is left back at the shop. However, if you have a Yokogawa EJA-E or EJX-A series pressure transmitter it is not a problem. Yokogawa's Local Parameter Setting (LPS) gives you easy access to nine (9) basic parameters:
  • Tag Number
  • Unit of measure
  • Set LRV (4 mA)
  • Set URV (20 mA)
  • Damping Time
  • Transfer Function (Linear or Square Root)
  • Display
  • Calibrate LRV (Requires applied pressure)
  • Calibrate URV (Requires applied pressure)
The LPS allows you to make changes to the transmitter without actually having a handheld communicator or FieldMate.

Friday, May 18, 2018

Wireless Instrumentation Promises to Improve Plant Efficiency, Mitigate Risk, and Increase Productivity

Yokogawa Wireless pressure transmitter
Wireless pressure
transmitter (Yokogawa)
Industrial companies are under great pressure to improve safety, reliability, and efficiency. Plant managers are faced with maintaining profits in face of greater competition and rising costs. Lost production, escalating energy costs, unexpected maintenance problems, and heightened safety concerns are always on the horizon. Situations such as unplanned shutdowns and outages due to equipment failure can be devastating to plant performance. Keeping personnel safe in dangerous or hazardous areas requires strict and deliberate attention to procedure. To address these concerns (reduce risk, save money, improve performance) higher reliability, and feature rich process technologies must continually evolve. Wireless instrumentation is one such technology. These new products deliver a promise to improve plant efficiency, mitigate risk, and increase productivity.

Yokogawa wireless gateway
Wireless gateway
Today's wireless instruments are available for monitoring virtually any process control variable including flow, pressure, level, temperature, pH, Dissolved Oxygen, etc..., or to monitor atmospheres for unsafe levels of toxic or combustible gases. These devices reliably transmit critical control and safety data back to central monitoring systems without the need for human supervision.

The argument for wireless instrumentation is very compelling when you consider installation convenience and cost savings.  Some cost savings estimates run as high as 70%  by eliminating wires and cables, as opposed to the cost when using cables for the same application. And most remarkably, wireless instruments provide additional safety and compliance benefits by keeping maintenance personnel out of dangerous or hazardous areas.

Wireless, portable gas detection
Wireless, portable gas detection
(Drager X-zone 5500)
In the process control industry, there are many reasons to adopt wireless instrumentation, but the acceptance by companies has been slow.  Why is this?  The fiscal argument for the industry to adopt wireless instrumentation networks is convincing as wireless is one of the more promising cost cutting technologies.

Impediments to Wireless
  • Reliability and Familiarity - Wireless must provide the same reliability (real and perceived) as traditional wired units, and engineers, operators, and maintenance staff must become just as comfortable with wireless as they are with wires and cables.
  • Working Within the Existing Infrastructure - Sometimes it doesn't make sense to build or relocate infrastructure or equipment just to create a reliable wireless link.  
  • Integration with Existing Communications - Concern over the impact on engineers, operators, and maintenance because of their work with the other, existing, field communications systems.

Drager wireless gateway
Drager wireless gateway
Industries will always be faced with cost cutting. A plant manager's job is continuous process improvement. There is always a need for better control solutions, and wireless instruments are promising. As the adoption of wireless instrumentation accelerate, concerns about reliability, user comfort,  infrastructure, and integration will subside. Industry-wide acceptance will be driven by deployment and maintenance savings, improved safety and easier governmental compliance.

Friday, May 4, 2018

7 Ways Thermal Mass Flow Meters Can Help Cut Wastewater Treatment Aeration Energy Costs

FCI Thermal Mass Flow Meter
One of the biggest expenses in wastewater treatment operations is the cost of energy to run the blowers and compressors that produce air for the aeration basins. The figures most often cited are that 40 to 50 percent of a wastewater plant’s total energy usage can be attributed to the aeration process.

By measuring the system’s air flows with accurate, repeatable air flow meters, the aeration process can be better controlled to optimize the process and minimize plant energy cost. Three flow sensor technologies typically have been used in aeration air flow monitoring applications in wastewater treatment plants:

Within wastewater treatment plant aeration systems, it is now generally accepted that thermal dispersion mass flow meters are the preferred, proven best solution and have the largest installed base. For plant expansions, new plants and upgrades this trend is expected to continue. The embedded document below presents seven tips that explain how thermal mass flow meters can reduce aeration plant energy costs and have become the flow meter of choice for aeration applications.

Alternatively, you can download your own copy of "7 Tips to Cut Wastewater Aeration Energy Costs with Thermal Mass Flowmeters" here.

Saturday, April 28, 2018

Flameless Explosion Venting

Explosion test
Explosion test without flameless vent.
(Courtesy of Fike)
In the event of a plant explosion, the flames and dust exiting the process vessel threaten a plants personnel, equipment and property. In a normal venting situation, an explosion is freely discharged, with threatening dusts and flames exiting the process vessel. The dust and flame are then channeled down vent ducts and ultimately outside the building. The ductwork has disadvantages though, and indoor plant installations cannot be protected by explosion vents alone.

Flameless venting is highly suited for indoor applications and, used in in combination with explosion vents, can extinguish the flame from the vented explosion without the use of expensive ducting, limitations to equipment location, or more costly explosion protection.  Flameless explosion venting protects people and equipment from flames and dust by using a flame absorber with a mesh filter to rapidly and efficiently cool and extinguish the flames immediately.
Explosion test
Explosion test with flameless vent.
(Courtesy of Fike)

Flameless venting is a viable alternative to ducting.  Since indoor venting is not permitted, the designer has to select between vent ducting and flameless venting, and sometimes flameless explosion venting is the only alternative.

Advantage of Flameless Venting:
  • Eliminates need for expensive ducts
  • Enhanced venting efficiency over venting with ductwork
  • Virtually maintenance free
Explosion venting system designers must take design standards into consideration in order to ensure that the calculated relief area and selected venting devices are compliant with local codes and laws.

Flameless venting must consider venting efficiency and incorporate it in the overall design. The venting efficiency factors of the venting and flameless venting devices are manufacturer product specific, can be application specific and should be used in accordance with the manufacturers’ recommendations only.

It is also critical to discuss your explosion venting application with an applications expert. Gaining their  knowledge and experience can literally mean the difference between success and disaster.

Tuesday, April 17, 2018

Flow-Tech, Inc. Serving Maryland, Washington D.C. and Virginia

Flow-Tech is a manufacturer’s representative and stocking distributor of process instrumentation and calibration equipment in Maryland, D.C and Virginia specializing in the Industrial Process, Control, and Test / Measurement markets.
410-666-3200 MD
804-752-3450 VA

Monday, April 9, 2018

What is a Pressure Transmitter?

Differential pressure transmitter
Differential pressure
transmitter (Yokogawa)
A pressure transmitter is a transducer that converts pressure into an electrical signal it outputs both analog and digital signals corresponding to the pressure. A pressure transmitter measures three phenomena: differential pressure; gauge pressure; and absolute pressure. The most common and useful industrial pressure measuring instrument is a differential pressure transmitter. This instrument senses the difference in pressure between two ports and produces an output signal with reference to a calibrated pressure range.

Industrial Applications of Pressure Transmitters

Pressure transmitters are commonly used to measure the pressure inside of industrial machinery or in industrial processes. They are used in various industries such as oil and gas, refining, chemical, pharmacy, and so on.

Pressure Transmitters in Industry

Pressure Transmitters in Industry
Pressure Transmitters in Industry
Pressure transmitters are widely used in industry to measure flow, level, and pressure. There are unlimited industrial applications. Oil and gas flow metering applications are found onshore, offshore and in subsea. It is also often used for monitoring filters in water and effluent treatment plants, monitoring sprinkler systems, and remote sensing of heating systems for steam or hot water. It can monitor pressure drops across valves and can be used to monitor pump control.

Differential Pressure for Flow Measurement

DP flow measurement is one of the most common applications for differential pressure transmitters by measuring the difference in fluid pressure. While the fluid flows through a pipe, it is possible to calculate the flow rate for differential pressure flow measurement. A primary and the secondary element are used. The primary element is designed to produce a difference in pressure as the flow increases. There are many different types of primary element, the most common being the orifice plate, Venturi flow nozzle, and pitot tube. The secondary element is a differential pressure transmitter. It is designed to measure the differential pressure produced by the primary element as accurately as possible. In particular it is important that the differential pressure measurement is not affected by changes in the fluid line pressure, temperature, or other properties such as ambient temperature. A good DP transmitter will ensure that the differential pressure is measured accurately regardless of other changing parameters and will reliably transmit a signal to represent the differential pressure. The DP flow transmitter output signal may also include square root extraction for flow calculation, although it is common for this function to be handled in a control system. In a typical control loop, the transmitter signal is fed to the controller whose output is used to regulate the flow rate through a control valve.

Differential Pressure for Flow Measurement
Differential Pressure for Flow Measurement

Differential Pressure for Level Measurement

Differential pressure transmitters can also be used for tank levels by measuring the pressure. The transmitter is installed at the bottom of the tank whose level is to be detected. In case of a sealed tank, a transmitter with capillaries measures a differential pressure between the upper side and the bottom side. The liquid inside the tank at the bottom creates pressure which is higher than the pressure at the top. The difference in these pressures can be used to calculate the level. In case of an open tank, the transmitter measures the differential pressure between the liquid inside the tank and the reference atmospheric pressure. In a typical control loop, the transmitter signal is fed to the controller whose output is used to regulate the tight level through a control valve.

Differential Pressure for Level Measurement
Differential Pressure for Level Measurement

Friday, March 30, 2018

Flow-Tech, Inc. - Process Instrumentation, Calibration, Safety, Measurement and Control

Flow-Tech is a manufacturer’s representative and stocking distributor of process instrumentation and calibration equipment in Maryland, D.C and Virginia specializing in the Industrial Process, Control, and Test / Measurement markets. Customers include: Power and Chemical plants, OEM’s, System Integrators, Municipalities, Engineering Firms, Universities, Medical Centers, and Research / Metrology Labs. Products and systems focus on the measurement and control of: flow, pressure, temperature, and level; as well as calibration equipment, analyzers, gas detection, annunciators, and data acquisition. Flow-Tech also provides field service, turn-key systems, equipment start-up, service contracts, and training.

Tuesday, March 27, 2018

Understanding Flow Sensing Technologies

When selecting a flow sensor, flow meter, or flow switch, one of the first considerations is always the process media: air, gas, steam or liquid. Some flow sensing technologies measure gas, some are better at liquids, some are best for a single media, such as steam, and others are good in multiple media. The industry’s major flow sensing technologies now available include:
Thermal flow meters.
Depending on the process media and your application’s requirements, all of these technologies have their advantages/ disadvantages. By considering the process media to be measured, as well as your plant’s equipment and layout, environmental conditions, maintenance schedules, energy cost and ROI, you will be able to narrow the field to one or two best choices.

Coriolis (Mass): Coriolis flowmeters use the oscillating movement of two symmetric metal tubes that are made to vibrate from an internal driver coil.  When liquids or gases flow through the tubes, a phase shift occurs (like you see in the hose) and pickups measure the “twist” and then relate that value to the actual flow. In other words, the amount of twist is proportional to the mass flow rate of fluid passing through the tubes. The greater the twist, the larger the distance between, and the greater the flow.

Differential Pressure: The differential flow meter is the most common device for measuring fluid flow through pipes. Flow rates and pressure differential of fluids, such as gases vapors and liquids. The differential flow meter, whether Venturi tube, flow nozzle, or orifice plate style, is an in line instrument that is installed between two pipe flanges and measures the pressure drop across the flow restrictor and equates it to flow.

Electromagnetic: Magnetic flow meters, also called electromagnetic flow meters or "magmeters",operate on a very simple principal. An electrically conductive liquid moving through a magnetic field will generate a voltage that is related to the velocity of the liquid.

Positive Displacement: Provides a direct indication of actual volumetric flow rate. The fluid motion drives the mechanical assembly. As the fluid motion drives the positive displacement flowmeter assembly, its rotational, oscillating, or other regular movement is counted, often by electronic means using magnetic pickups on moving assembly. There are a number of different positive displacement flowmeter designs including oscillating piston, gear, nutating disk, rotary vane, and diaphragm.

Thermal (Mass): Measure flow by delivering heat into the flowing media and measuring the loss of heat between temperature measurement points. They are popular because they provide unrestricted flow, contain no moving parts, work well on large or small diameter pipes, provide accuracies over a wide range of flow rates, do not require temp/press compensation, and provide mass flow instead of volume.

Turbine: These types of flowmeters operate under the simple principle that the rotation of the turbine will be constant as the turbine is acted upon by a fluid passing through the flowmeter. The rotational velocity of the turbine is then interpreted as output, allowing for the operator to consistently monitor the flow rate of the process fluid. They are easy to maintain and reliable.

Ultrasonic: Measure, via sound waves, the velocity of liquid flowing through a pipe.  Doppler shift technology reflects ultrasonic beams off sonically reflective materials. The transit time method exploits the fact that the transmission speed of an ultrasonic signal depends on the flow velocity of the carrier medium. The use of ultrasonic flow technology is most used in the oil, nuclear, wastewater, pharmaceutical, food and beverage industries.
Variable Area
Variable Area

Variable Area: Measures flow rate by allowing the cross-sectional area the fluid travels through to vary, causing a measurable effect. Flow measurement is performed according to the float principle. Used to measure many different types of liquids and gases passing through closed piping.

Vortex Shedding
Vortex Shedding: Refers to the phenomenon wherein flowing gas or liquid forms vortices around a solid obstruction placed in the flow path, which can be measured to calculate volumetric or mass flow. Measure the volumetric flow rate of steam, gas, and low viscosity liquids.

Contact Flow-Tech for any industrial or commercial flow application by calling 410-666-3200 in Maryland, or 804-752-3450 in Virginia. Visit

Wednesday, March 21, 2018

Draeger Gas Detection Transmitter and Feature Selection Charts

Here are two charts to help you select Draeger Gas Detection Transmitters.

The diagram below provides a flow chart on how to properly select a Draeger transmitter.

Draeger Transmitter Selection Flow Chart
Draeger Transmitter Selection Flow Chart (click for larger view).

The table below provides a feature comparison table for most Draeger transmitters (it does not show the PointGard 2100, but the P8100 features are very similar, if not identical).

Draeger transmitter feature comparison table
Draeger transmitter feature comparison table
(click for larger view).

Tuesday, March 13, 2018

The Ideal Flow Monitoring System for a Drinking Water Supply Network

The ideal drinking water flow monitoring system.
Wouldn't it be great if you had a closely woven system of measuring points that monitor flow rates in the drinking water supply network as seamlessly as possible and leaks and hydrological problem zones would be detected and corrected as quickly as possible?

Unfortunately the reality looks somewhat different. Installation of conventional flow measuring points in a drinking water supply network incurs high costs and an enormous amount of effort to maintain.


FLEXIM is a technology leader in the field of non-invasive flow measurement with clamp-on ultrasonic technology. FLEXUS clamp-on ultrasonic systems measure according to the transit time difference method. Since the transducers are mounted on the outside of the pipe no interventions in the pipeline system are necessary. the drift free and long-term stable acoustic measuring method detects even the smallest flows, even those that lie below the response threshold of conventional flow meters. Therefore, fluxes is the ideal instrument for monitoring minimum flow rates at night, and thus the key to effective consumption and leakage monitoring.

With FLEXUS, a flow measuring point can be conveniently setup within half a working day without supply interruptions with out affecting traffic, and without a heavy lifting device.  For the installation of the ultrasonic measuring system, only temporary access to the pipe has to be created.  The service engineer first checks the pipe dimensions. Sturdy mounting devices made of stainless steel ensure that the flow transducers are permanently stable when installed. Even on the transducers themselves, nothing can break. The cable and sensor are firmly connected. No plug can come loose. Water or dirt cannot penetrate anywhere. The ultrasonic transducers have IP68 protection and can operate continuously underwater. Coupling pads, made of elastic plastic, ensure permanent optimal acoustic coupling to the pipe without any wear. Thanks to their unique internal temperature compensation, FLEXIM transducers do not show any drift during temperature fluctuations. Setup of the measuring point on the pipe is completed by positioning and fixing the ultrasonic transducers. Now only the connection to the measuring transmitter, housed in the switch cabinet, has to be created. The calibration data of carefully paired and calibrated transducers are stored on one chip and are automatically transferred to the measuring transmitter. A zero point calibration on site is not necessary. Where nothing flows, FLEXUS reliably measures zero.

Measurement in Progress

The measuring results are either transmitted by cable or wirelessly via GSM to the process control system. Practical self-diagnosis functions allow for safe evaluation of the measurement quality. Done. Now the measuring point can be refilled underground since the pipe line remained completely intact. There was no need to flush the pipe and no need for the final leak test. In the office, the measured values can be visualized and evaluated on a computer.

Sunday, February 25, 2018

Bently Nevada 3500 Series Machinery Monitoring System Datasheet

Bently Nevada 3500 Series Machinery Monitoring System
Machine condition monitoring combines hardware, software, and service and support – providing a broad, connected view of your operations. Together, they enable your plant to mitigate risk, boost safety, and reduce maintenance costs, while improving equipment reliability, uptime, and efficiency.

Hardware monitoring systems and sensors protect your equipment and collect rich condition monitoring and diagnostic data for analysis. Condition monitoring and diagnostics software connects real-time and historical data from production equipment to help you anticipate failure before it occurs. With scalable deployment and ongoing support service offerings, you can ensure that you’re maximizing the value of your condition monitoring program.

The Bently Nevada 3500 Monitoring System provides continuous, online monitoring suitable for machinery protection and asset condition monitoring applications. It represents our most capable and flexible system in a traditional rack-based design and offers numerous features and advantages not provided in other systems.

Download a PDF version of the Bently Nevada 3500 System datasheet here, or quickly review the embedded document below.

For more information, contact Flow-Tech in Maryland by calling 410-666-3200, in Virginia by calling 804-752-3450, or by visiting

Friday, February 16, 2018

Campus Metering: Advantages of Using V-Cone for Measuring Chilled Water & Steam in Hospitals, Universities, and Institutions

McCrometer's V-Cone
Typical diagram of V-Cone installation.
(Click for larger view).
McCrometer's V-Cone® Flow Meter is an advanced differential pressure instrument, which is ideal for use with liquid, steam or gas media in rugged conditions where accuracy, low maintenance and cost are important. The V-Cone is especially useful in tight-fit and retrofit installations. 

In most instances the use of V-Cones associated with chillers for chilled water in large institutional users is a matter of space, accuracy, and turndown. The V-Cone needs very little upstream and downstream piping requirements, allowing it to be used in spaces where other meters cannot be used, or to replace existing flowmeters that never proved accurate because of space limitations. 

In many large universities and other facilities, such as hospitals and airports, across the U.S., the reason for initial interest and subsequent purchases of V-Cones to measure Chilled Water was to fit within the confines of the existing and new buildings that were being used to house the chillers. Additionally, the second most important reason was the delivered accuracy. In the past, most usage had been ignored, but with the rising costs associated with cooling, each individual building must be accountable for individual use. This is just good fiscal responsibility and management from an energy balance standpoint. Turndown was an issue because of seasonal swings in usage based on climate and population in the buildings at any particular time. Therefore, the meters needed to be able to have a large flow span (turndown), which remained accurate during continuous use.
McCrometer's V-Cone
Internal view of V-Cone.

V-Cones have recently been selected for Steam service for mostly the same reasons as they are selected for Chilled Water. Space limitations in new and/or older buildings are a serious concern. V-Cones have the smallest piping requirements of practically any flowmeter and continue to deliver accurate measurement, so they are fiscally responsible and cost effective. Additionally, in steam, they allow condensate and/or other small particulate matter to pass without affecting the measurement, thus giving much better accuracy instantaneously and over time. 

They are very rugged flowmeters which require little or no maintenance, and have a very long expected life even in “tough” service like steam. They can be designed with great turndown (span) and therefore can accommodate changes in flowrates based on demand, seasonal or from other factors.

For more information on V-Cone flowmeters, contact Flow-Tech in Maryland at 410-666-3200, in Virginia at 804-752-3450, or by visiting

Wednesday, February 7, 2018

How To Select a Gas Flow Meter for Your Application

Gas Flow Meter

Here is some very good, basic advice, courtesy of FCI (Fluid Components International) on selecting a gas flow meter.

Match your application to the appropriate measurement technology. Accurate flow measurement starts with selecting the best flow meter technology for your application. Every application has a set of requirements that narrows the choice of technologies. For example, thermal dispersion might work best in a dirty process gas, like biogas, because this technology provides no-moving-parts reliability, direct mass flow measurement, and wide range ability. However, positive displacement might be the best technology choice for the custody transfer of natural gas.

An Instrument Specification Sheet is a good place to find information that will help select the most appropriate flow meter technology for an application. This sheet identifies the application's process temperature and pressure, gas composition, piping configuration, accuracy requirements, and more.

Now forward your application information to vendors that offer the most appropriate flow meter technology. Be sure to include as much information about the application as possible and highlight your realistic performance expectations. Do not request 0.5 percent accuracy if the application needs only 5 percent accuracy. Ask these vendors to evaluate your application and provide a product recommendation. Use the information you receive to revise your specification (if necessary), finalize your preferred vendor list, and prepare your request-for-quote.

FCI flowmeters
Contact Flow-Tech for any flow meter application you may have. Our support engineers are ready to help.

In Maryland - 410-666-3200
In Virginia - 804-752-3450

Wednesday, January 31, 2018

Differential Pressure Level Detectors

Differential Pressure Level
Fig 1. Open Tank Differential Pressure Detector
Click for larger view
The differential pressure (∆P) detector method of liquid level measurement uses a ∆P detector connected to the bottom of the tank being monitored. The higher pressure, caused by the fluid in the tank, is compared to a lower reference pressure (usually atmospheric). This comparison takes place in the ∆P detector. Figure 1 illustrates a typical differential pressure detector attached to an open tank.

The tank is open to the atmosphere; therefore, it is necessary to use only the high pressure (HP) connection on the ∆P transmitter. The low pressure (LP) side is vented to the atmosphere; therefore, the pressure differential is the hydrostatic head, or weight, of the liquid in the tank. The maximum level that can be measured by the ∆P transmitter is determined by the maximum height of liquid above the transmitter. The minimum level that can be measured is determined by the point where the transmitter is connected to the tank.

Differential Pressure Level
Fig. 2 Closed Tank, Dry Reference Leg
Click for larger view
Not all tanks or vessels are open to the atmosphere. Many are totally enclosed to prevent vapors or steam from escaping, or to allow pressurizing the contents of the tank. When measuring the level in a tank that is pressurized, or the level that can become pressurized by vapor pressure from the liquid, both the high pressure and low pressure sides of the ∆P transmitter must be connected (Figure 2).

Differential Pressure Level
Fig 3 Closed Tank, Wet Reference Leg
Click for larger view
The filled reference leg applies a hydrostatic pressure to the high pressure side of the transmitter, which is equal to the maximum level to be measured. The ∆P transmitter is exposed to equal pressure on the high and low pressure sides when the liquid level is at its maximum; therefore, the differential pressure is zero. As the tank level goes down, the pressure applied to the low pressure side goes down also, and the differential pressure increases. As a result, the differential pressure and the transmitter output are inversely proportional to the tank level.

Where the tank contains a condensible fluid, such as steam, a slightly different arrangement is used. In applications with condensible fluids, condensation is greatly increased in the reference leg. To compensate for this effect, the reference leg is filled with the same fluid as the tank. The liquid in the reference leg applies a hydrostatic head to the high pressure side of the transmitter, and the value of this level is constant as long as the reference leg is maintained full. If this pressure remains constant, any change in ∆P is due to a change on the low pressure side of the transmitter (Figure 3).
410-666-3200 in Maryland
804-752-3450 in Virginia

Monday, January 29, 2018

Understanding Hydrostatic Pressure in Process Control

Hydrostatic pressure transmitter
Transmitter used to measure
hydrostatic pressure. (Yokogawa)
The pressure exerted by a fluid material in a vessel is directly proportional to its height multiplied by its density.

Hydrostatic pressure, or head pressure, is the force produced by a column of material. As the height of the material changes, there is proportional change in pressure. To calculate hydrostatic pressure, the density of the material is multiplied by the height of the column. The level of fluid in a column can be determined by dividing the pressure value by the density of the material.

To find pressure in a column of water, a gauge placed at the bottom of the vessel. With the water having a density of 0.0361 pounds per cubic inch, the level of the fluid is calculated by dividing the head pressure by the density of the fluid.

An example to determine the level measurement of a column of water that is 2 feet tall in diameter of 0.5 feet is solved by the following steps. The first step is measuring the weight of the vessel. Next measure the weight of the vessel with fluid. The weight of the fluid is determined by subtracting the weight of the vessel from the weight of the vessel with fluid. The volume of the fluid is then derived by dividing the fluid weight by the density of the fluid. The level of the fluid is finally calculated by dividing the volume of the fluid by the surface area.

Hydrostatic pressure can only be calculated from an open container. Within a closed vessel, or pressurized vessel, the vapor space above the column of material adds pressure, and results in inaccurate calculated values. The vessel pressure can be compensated for by using a differential pressure transmitter. This device has a high pressure side input and a low pressure side input. The high-pressure input is connected to the bottom of the tank to measure hydrostatic pressure. The low-pressure input of the differential pressure transducer is connected to the vapor space pressure. The transducer subtracts the vapor pressure from the high-pressure. Resulting is a value that represents the hydrostatic head proportional to the liquid level.

Saturday, January 20, 2018

Tank Overfill Protection

Tank Level Control
Tank Level Control Diagram (Yokogawa)
Protecting against tank overfill allows for process control industry professionals to mitigate potential risk to both their processes and process materials. Different products present different risks regarding tank overfill, but the work of preventing overfill is a universal component of safety, procedural effectiveness, and maximization of resources. If tank overfill does occur, a number of potential negative outcomes could result, especially in the cases of wastewater, chemicals, and petroleum products. Everyone, from management to methodology, needs to be working from the same ideal regarding safety as an inherent priority of process control.

Instead of solely focusing on tank overfill prevention, many corporations have developed written instructions for every individual operator in an organization. Not only do these standards adhere to regulations, but they also meet environmental standards while eliminating accident risk. Six Sigma is an example of data-driven management meant to eliminate potential defects in safety procedures. The idea of pursuing perfection in all components of an organization may originally seem far away from overfill protection. However, previous attempts to confront tank overfill without consideration for the larger organization narrowed operational windows to only consider one part of the system.

Expanding this system to include root causes of overfill prevention instead of solely the mechanisms for prevention has resulted in a more holistic approach to the integration of safety standards. Regulatory requirements for tank metrics, how to operate aboveground versus below ground tanks, and process material specific guidelines are combined with internal company codes. Those two elements are then fused with the Recognized and Generally Accepted Good Engineering Practices which are developed by industry associations. The tri-part approach has resulted in a more collaborative effort to combat tank overfill problems.

One metric employed to prevent tank overfill-related dangers is to measure whether or not the tank in question has the appropriate room to accommodate abnormal process behavior. Considerations such as these mesh with evaluations of pipe size and whether or tanks need to be connected to relief tanks. Assessment of both operational and insurance risk means the entirety of the process must be understood and evaluated so that the interaction between the process materials can be predicted and then mitigated. Whether these components are raw materials, system components, or final products in the latter stages of the process, automated systems combined with operator diligence based on established methodology is the best way to prevent overfill and associated dangers.

To discuss your tank level control and overfill requirements, contact Flow-Tech at or call 410-666-3200 in Maryland, or 804-752-3450 in Virginia.

Saturday, January 13, 2018

How to Adjust Alarms and Pointer for Brooks Instrument Models MT3809G & MT3810G Variable Area Flowmeters

Here are the instructions for the removal and reinstallation of the XP housing indicator cover, and
how to adjust alarms and pointers for Brooks Instrument models MT3809G & MT3810G variable area flowmeters:

Warning: If it becomes necessary to service or remove the instrument from the system, power to the device is disconnected at the power supply.
  1. To begin make sure the float is at rest and there isn’t flow going through the meter.
  2. Using your hands or a strap wrench turn the cover counter clockwise to remove the cover from the housing.
  3. Remove the cover from the housing. The gasket should stay attached to the groove in the housing.
  4. Using a flat blade screwdriver with a 1/8" blade, hold the red alarm pointer and turn the screw counterclockwise to loosen the pointer, slide it to desired position on scale and tighten screw.
  5. Using a flat blade screwdriver with a 1/8" blade, hold the pointer and turn the screw to align with the “R” on the scale. It may take a few adjustments to get the pointer aligned to the “R”.
  6. To replace the cover, place the cover against the housing and turn the cover clockwise. Note, it will take several rotations to tighten the cover and the cover must be in contact with the gasket to keep a watertight seal.

MT3809G & MT3810G variable area flowmeter
Click for larger view.
For additional assistance, contact Flow-Tech in Maryland at 410-666-3200 or Virginia at 804-752-3450 or visit