Liquid Level Measurement Using the “Bubbler Method”

January 29th, 2016 No comments

Liquid Level Measurement Using the Bubbler Method
General chemical industry applications where liquids are stored in tanks.

Measurement of the level of a liquid in a tank using a pressure transmitter to measure the pressure created by the weight of the liquid. The key feature of this method is the use of a small diameter (typically ¼”) tube installed in the tank to allow the pressure measurement to be taken at the top of the tank, eliminating potential leak points at the bottom of the tank.

Process Details
The pressure measured at the bottom of a tank of liquid will be proportional to the level of the liquid in the tank according to the relationship:
Height of liquid = Pressure at bottom of tank / density of liquid.
To avoid possible leak points, the pressure measurement can be taken at the top of a “dip tube” installed in the tank as shown in the diagram above. The key to this method is the introduction of a low rate of gas flow in the tube, effectively transferring the pressure at the bottom of the tank to the inlet of the tube (plus the small pressure drop created by the flow rate in the tube).
To keep the pressure drop low in the tube, a flow rate of 1.0 SCFH is typical for a ¼” diameter dip tube. This minimizes the offset in the level measurement created by this pressure drop.

Using a Brooks Instrument Model 1350G purgemeter with a Model FCA8900 integral downstream flow controller will keep the flow rate constant in the dip tube with the varying downstream pressure caused by the varying liquid level. This further improves the accuracy of the measurement by keeping the offset constant.
The supply pressure to the flowmeter should be set to a value high enough to overcome the back pressure of the liquid level and the minimum pressure drop needed across the flow controller. A supply pressure of 25 psig would be adequate for tank levels up to 30 feet. The flowmeter scale should be sized (i.e. compensated) for this supply pressure.

Also available from Brooks is the SolidSense II® pressure transducer for the primary electrical output.
Brooks Instrument has been a supplier of choice for this application for many years, and to several industries, including petroleum refining, electrical power and semiconductor.

Selecting the Right Elastomer Seal Material for Mass Flow Controllers and Variable Area Flow Meters (Rotameters)

December 30th, 2015 No comments

Elastomer seal material selection is not always a clear cut decision. Many factors must be considered:

  • Fluid
  • Temperature
  • Pressure (Max, Min, Differential)
  • Application (static or dynamic)
  • Price
  • Customer’s experience

Most major seal manufacturers offer material compatibility information and material selection guides. Compatibility ratings are based on a manufacturer’s compound/material in a specific service. Published compatibility guides list one service at a time (glycol) at a nominal temperature (70º F).

While Brooks Instrument should not be considered an expert in elastomers, we will make recommendations based on our prior application experience. The final decision is of course, always up to the customer. To aid with your next decision on elastomer seal material the following are generic elastomer property descriptions for materials found in Brooks mass flow controllers and variable area flow meters (rotameters):

Fluorocarbon, VITON® (FKM):

VITON® is the trade name for DuPont Performance Elastomers Fluorocarbon or FKM material. FKM has a temperature range of -20F to +400F, and provides excellent resistance to a wide variety of chemicals, weather and compression set requirements. The relatively high level of fluorine in FKM materials allows for exceptional resistance to chemical attack, but with limited low temperature capabilities. Brooks offers FKM elastomers manufactured to conform with FDA and USP Class VI requirements, making it ideal for use with bio-pharm applications and medical devices.

Nitrile, Buna-N (NBR):

Nitrile, also known as Buna-N or NBR, is a copolymer of Butadiene and Acrylonitirle. It is the most commonly used elastomer for sealing products. It has a temperature range of -40F to +250F and is exceptionally resistant to petroleum based oils and hydrocarbon fuels. Nitrile materials also exhibit excellent tensile strength and abrasion resistance properties. The material performs well with most diluted acids, silicone oils and lubricants and in water applications. It is not recommended for use with ketones, aromatic hydrocarbons and phosphate ester hydraulic fluids.

Kalrez® Perfluoroelastomer (FFKM):

Kalrez® Perfluoroelastomer (FFKM) currently offers the highest operating temperature range up to 320°C (608°F), the most comprehensive chemical compatibility, and the lowest off-gassing and extractable levels of any rubber material. FFKMs deliver an extreme performance spectrum that make them ideal for use in critical applications like semiconductor chip manufacturing, jet engines and chemical processing equipment.

Ethylene Propylene, EPDM, or EP (EP):

EP is a copolymer of ethylene and propylene, while EPDM is a terpolymer combining ethylene, propylene and a diene monomer. EP materials offer a temperature range of -65F to +300F and offer excellent resistance to ozone, weathering, steam, water and phosphate ester type hydraulic fluids. Brooks offers EPDM elastomers manufactured to conform with FDA and USP Class VI requirements, making it ideal for use with bio-pharm applications and medical devices.

For exact product temperature ranges or material availability on a specific product, please refer to our product data sheets. Our long-tenured team of applications engineers will provide guidance, if requested, during the product selection and configuration process.

Handling Pressure Variation With a Mass Flow Controller

November 24th, 2015 No comments

Industries: Petrochemical research, Alternative Fuels research

Application: Downstream destination of the fluid (normally gases) is a reactor vessel and the test requirements are broad from a pressure standpoint. This would typically apply when the pressure exceeds 200 PSIG.

optimum mfc system setup


Process Details and Specifications

Gases can range from hydrocarbons (i.e. methane, ethylene) to air, nitrogen, carbon monoxide and carbon dioxide. Pressures in the reactor vessel can range from a few hundred PSIG to several thousand PSIG.

Since an MFC is a closed loop control system with a valve that is sized for a specific set of conditions for optimum performance, pressure variations can significantly impact the performance of the valve. Simply stated, if an MFC is sized for higher pressures, then use at low pressures may result in an inability to achieve the required maximum flow through the valve. If an MFC is sized for lower pressures, then use at higher pressures may result in an oversized valve that is attempting to operate close to the fully closed position.


The Brooks SLA Series MFC’s are particularly suited for these types of applications for two reasons:

- High pressure capability: up to 4500 PSIG operating pressures

- Brooks in-house valve sizing capabilities

Although research applications are all unique and can change over time, Brooks has the capability, both at the factory and with our sales partners, to provide expert consultation over a wide range of operating conditions. We’ll evaluate your specific needs to find a workable set of conditions to cover most, if not all, of your research testing needs.

The result is a reduction in the number of MFC’s needed to cover the entire range of your research, and eliminating the possibility of inadequate MFC performance, ensuring that all of your test data can be used.

Brooks has worked with all of the major petrochemical research facilities around the world, as well as many universities supporting these high pressure applications.

Categories: Coriolis and Thermal Mass Flow Tags:

Understanding Mean Time Between Failure (MTBF) for Process Instrumentation

October 28th, 2015 Comments off

Mean Time Between Failure (MTBF) is a measure of the reliability of a hardware product, component or system. MTBF is largely based on assumptions and the definition of failure and attention to these details is important for proper interpretation. For complex, repairable systems, failures are considered to be those conditions which place the device or system out of service and into a state for repair. Failures that can be left in an unrepaired condition, and do not place the device or system out of service, are not considered failures under this definition. In addition, units that are taken down for routine scheduled maintenance or inventory control are not considered within the definition of failure.

Brooks Instrument Illustrates How to Calculate Mean Time Between Failures (MTBF)

Calculating Mean Time Between Failures (MTBF)


The MTBF should not be confused with the life expectance. An example is the best way to describe the difference. All humans have a life expectance of 80 years or 700,800 hours. However, the human body fails at different rates depending on its age.

There are 500,000 25-year-old humans in a sample population. Over the course of a year, data is collected on deaths for this population. Throughout the year, 625 people died. The MTBF is (500,000/625)x24x365 = 7,008,000 hours (800 years). So, even though 25-year-old humans have high MTBF values, their life expectancy (service life) is much shorter and does not correlate.


How is MTBF calculated?

The Mean Time Between Failures (MTBF) of a product is determined using the following equation[1]:

Mean Time Between Failure (MTBF) Equation

Mean Time Between Failure (MTBF) Equation


F = number of failures per year divided by the number of units shipped per year


How do Brooks Instrument Mass Flow Controllers (MFCs) stack up?

With the largest installed base of thermal mass flow controllers and mass flow meters around the world, Brooks’ flow meters provide significant advantages in long term stability, response time, accuracy, repeatability, turndown, self-diagnostics and application flexibility.

Brooks Mass Flow Controllers and Mass Flow Meters offer:

  • Industry-leading long term stability ensuring consistent process results over the life of the device and a longer period between recalibrations
  • Self diagnostics and alarms minimize downtime
  • Multiple communication protocols allow easy integration into many control systems
  • Analog I/O devices allow for quick and easy system integration
  • Elastomer seal option provides good leak integrity and control valve shutoff dependability
  • Global approvals for a variety of service areas

Brooks Instrument mass flow devices have industry leading mean time between failure (MTBF) which provides the user with maximum up time. MTBF for several SLA Series mass flow controller models is shown below.


Model Description MTBF (years)
SLA5850 Mass Flow Controller 63
SLA5851 Mass Flow Controller 118
SLA5853 Mass Flow Controller 59


This MTBF information is based on actual shipments and warranty returns over a 1.5 year period. This period includes the infant mortality phase shown in the “bathtub curve” below and as a result likely underestimates the MTBF.


bathtub curve

The Bathtub Curve illustrates hypothetical failure rate versus time


If you have questions about MTBF or any Brooks Instrument products or services please contact one of our applications engineers or your local Brooks Instrument sales expert.

[1] W. Torell & V. Avelar; “Mean Time Between Failure: Explanation and Standards”; APC White paper #78.

Safety First – Process Instrumentation Material Considerations

September 28th, 2015 Comments off

When specifying flow, pressure, temperature or other wetted process control instrumentation there is a lot that needs to be considered. Flow rates, pressures, temperatures, I/O signals, material selection, etc. In addition to all of this the specifier needs to be concerned with safety, certifications, approvals, material integrity, weld integrity and of course quality. I am writing this to make you aware of an element of the material integrity that should be considered when selecting a device and/or instrumentation supplier – hydrogen embrittlement.

Understanding Hydrogen Embrittlement
Hydrogen embrittlement is a type of material deterioration which can be linked to corrosion and corrosion-control processes. It involves the ingress of hydrogen into a component. Hydrogen, being a small molecule, in some situations readily diffuses through the metal crystal structure where it can accumulate and seriously reduce the ductility and load-bearing capacity. This may lead to cracking and catastrophic brittle failures at stresses below the yield stress of susceptible materials. Hydrogen embrittlement occurs in a number of forms but the common features are an applied tensile stress and hydrogen dissolved in the metal. Examples of hydrogen embrittlement are cracking of weldments or hardened steels when exposed to hydrogen rich environments. Hydrogen embrittlement does not affect all materials equally. The most vulnerable are high-strength steels, titanium alloys and aluminum alloys.

Some process instrumentation use high strength steel fasteners in the assembly. A hydrogen rich environment naturally occurs during the zinc plating process that is used to provide corrosion protection for many high strength fasteners. Special care must be taken in the manufacturing process of these high strength fasteners to ensure that they are not susceptible to hydrogen embrittlement.



Eliminating the Risk(s) of Hydrogen Embrittlement
Brooks Instrument eliminates the risk of hydrogen embrittlement by using 18-8 stainless fasteners where possible. The 18-8 stainless fasteners are corrosion resistant and immune to hydrogen embrittlement. All of the fasteners in Brooks Instrument size 0 mass flow devices (ex. SLA5850, 5850E, GF40 mass flow controllers) are 18-8 stainless. In the case where stronger screws are required, Brooks uses high alloy fasteners made by reputable manufacturers with tight control of the manufacturing and plating processes. We also require that all high alloy fasteners go through a high temperature baking process shortly after plating. This baking process drives out all harmful levels of hydrogen from the crystal structure. We also require that our suppliers certify each shipment. Because of these measures, Brooks has never had a field failure due to hydrogen embrittlement.

Brooks Instrument Solid Sense II pressure transducers, with single piece (non-welded) sensor and low internal volume, are proven products not susceptible to hydrogen embrittlement. The sensor was carefully designed with high purity 316L stainless steel material and does not require any internal sensor welding techniques. The Brooks Solid Sense II pressure transducer also utilizes a high temperature annealing process to enhance the sensor robustness ensuring stable performance over time in all gas delivery scenarios. The Brooks Solid Sense II has been selected as the right pressure transducer by gas cabinet manufactures, tool OEMs and end users around the world.

Some competitive pressure transducers have multiple piece designs requiring welding. Impurities introduced during chemical plating and/or welding operations, especially welding of dissimilar materials, may seed nucleation sites. These nucleation sites can result in hydrogen embrittlement which may lead to cracking and/or a change in sensor output. Pressure transducers impacted by hydrogen embrittlement failures could trigger a process or facility safety alarm impacting equipment availability resulting in very expensive maintenance and downtime.

When you are specifying process control instrumentation, be aware of the potential for hydrogen embrittlement and the associated safety concerns. Be sure to ask your suppliers how they minimize the risk of hydrogen embrittlement. Select a supplier that is aware of and has proactively taken steps to minimize the potential for hydrogen embrittlement.

For additional reading on fasteners, see, “The Nuts and Bolts of Bolting,” written by Joe Dille – Lead Mechanical Engineer at Brooks Instrument for over 32 years and published in BMW Motorcycle Owner’s Association – Owners News.

Electronic Pressure Controller Eliminates Droop, Boost and Hysteresis

August 31st, 2015 Comments off

Gas pressure control is critical in many applications like life sciences and chemical/petrochemical research where flow is an integral part of the process. Brooks Instrument electronic pressure controllers can be used as they require flow to function. Compared to using a mechanical pressure regulator, electronic pressure controllers eliminate droop, boost and hysteresis, offering stable pressure control.

There are two configurations available for pressure control – upstream and downstream. This terminology is somewhat unique to Brooks Instrument electronic pressure controllers.

Downstream vs. Upstream Pressure Control
Downstream pressure controllers maintain the pressure downstream of the device itself, increasing flow to increase the pressure and decreasing flow to decrease the pressure. For this reason, this is called direct acting. This configuration is commonly called a standard pressure regulator. A downstream pressure controller acts very similar to a typical mass flow controller because they are both direct acting.

Upstream pressure controllers maintain the pressure upstream of the device itself, increasing flow to reduce the pressure and decreasing flow to increase the pressure. For this reason, this is called reverse acting. This configuration is commonly called a back pressure regulator in the industry.


Selecting and Sizing an Electronic Pressure Controller
The following information is required to select and size a Brooks Instrument electronic pressure controller:

1. Process gas
2. Maximum flow rate being used to maintain pressure
-The “sweet spot” for pressure control is between 100 SCCM and 5 SLPM.
3. Calibration pressure (maximum pressure to be controlled)
4. Reference pressure (for upstream controllers the reference pressure is the downstream pressure and for downstream controllers the reference pressure is the upstream pressure)

As long as flow is present in a process you will typically find the need for some type of pressure control. Vessel sizes up to 30 liters commonly use flow rates up to 3 SLPM during their process steps. Brooks Instrument pressure controllers are a perfect fit for these services, offering stable pressure control with no droop, boost or hysteresis, which are commonly experienced when using a mechanical pressure regulator.


Typical Bioreactor Process Using an Upstream Pressure Controller

How do I correct my variable area flow meter for a gas with a different operating density? [FAQs]

September 27th, 2013 Comments off

Now for the “gas” version of the equation…

You want to get a quick flow check on a different gas because the process gas is changing or you might be experimenting with the process, but you don’t have a VA (variable area) flow meter that is calibrated for the different gas.

Enter the necessary information into the equation below and you’ll get the flow rate for the different gas.

Variable Area Flow Meter Gas Correction Equation

Things to Keep in Mind:

  • The meter has to be a size 8 (1/2” nominal size) or larger and of course the flow meter has to be capable of measuring the flow of the different gas.
  • Absolute Scale Unit Conversions:
    • psia = psia + 14.7
    • °R = °F + 460
  • If your experiment is successful, I recommend you get a meter so you don’t have to calculate the flow rate every time you use the different gas.

Visit our Knowledgebase page for more answers to your questions.

Our New GF81 High-Flow MFC Features the Shortest Lay Length on the Market

August 22nd, 2013 Comments off

Our new GF81 High-Flow MFC can be used for gas flow rates up to 300 slpm, making it ideal for high-flow applications in:

  • Thin film
  • Solar
  • Analytical
  • Biotech, and
  • Fuel cell

Here are a few reasons why we’re excited about this new product…

Design Smaller, More Efficient Systems
The compact footprint and low power draw of GF81 allows you to design smaller, more efficient systems. And, with the shortest lay length on the market, installation is easy making GF81 a simple drop-in replacement.


GF81 High-Flow Mass Flow Controller


One Product Series for All Your Process Gases
Since it’s part of our GF40 (elastomer seal) and GF80 (metal seal) Series, the GF81 uses the same high-stability sensor as its low flow siblings, guaranteeing stable, accurate and repeatable mass flow measurement.

The all metal seal flow path allows GF81 to handle almost any gas – including many corrosive and hazardous gases.

An Ideal Upgrade
A wide range of digital and analog I/O options offers the broadest range of communication protocols, making the GF81 an ideal upgrade for existing MFCs or MFMs. Now, you can upgrade to a device that offers better actual process gas accuracy and repeatability over devices that use traditional single-point conversion factors, while keeping the same communication protocols.

Want to Learn More?
The benefits we listed here are only part of the story. There’s more to share about how and why this robust family of devices can be used for a variety of applications.

We’d appreciate the opportunity to talk with you so please, post a comment, email us or call (1-888-554-3569) to speak with one of our flow experts.

How do I correct my variable area flow meter for a liquid with a different operating density? [FAQs]

August 15th, 2013 2 comments

You want to get a quick flow check on a different fluid because the process fluid is changing or you might be experimenting with the process, but you don’t have a VA (variable area) flow meter that is calibrated for the different fluid.


Enter the necessary information into the equation below and you’ll get the flow rate for the different fluid.


variable area flow meter

Correction Equation for Liquid Flow


Things to Keep in Mind:

  • The meter has to be a size 8 (1/2” nominal size) or larger and of course the flow meter has to be capable of measuring the flow of the different fluid.
  • If the new specific gravity is drastically different, the meter may not be capable of registering a flow rate for the new fluid.
  • If your experiment is successful, I recommend you get a meter so you don’t have to calculate the flow rate every time you use the different fluid.


Visit our Knowledgebase page for more answers to your questions.

What I learned at SEMICON West 2013

July 26th, 2013 Comments off

CelerityLogoIt never, ever fails – each time I get out of the office and into the marketplace, I come away with insights and ideas.

At SEMICON West 2013, there was so much to absorb about the industry, suppliers, competitors and customers. But when I hone in on my key insights and what they mean to Brooks Instrument and the people we have the honor of serving, this was numero uno:

What may be old news to us could be “new” news to the marketplace, for a very long time…

Here’s what I mean – back in 2009, Celerity, Inc. joined the Brooks Instrument family. Celerity brought its rich history of growth and innovation in the semiconductor market to Brooks, including well-known mass flow controller brands like:UnitMFC
• Celerity
• Unit
• Millipore
• Mykrolis
• Tylan General

Although we communicated this to the marketplace in a variety of ways, not a single visitor to our booth was aware. That means all of you out there who currently own one of these devices are missing out on getting the best factory certified service for your device as well as the opportunity to upgrade to the latest technology, like our GF100 Series thermal mass flow controllers. This technology platform has been designed to precisely measure, monitor, and control ultra high purity process gas chemistry in semiconductor device manufacturing processes.Mykrolis

We are here for you! If you’d like to know more, email or call us at 1-888-554-3569.