Managing pressure is a fundamental control challenge for most process manufacturers and producers. A frequent question is whether a pressure regulator or control valve is best for a particular application. At last fall’s Emerson Exchange, I live-blogged a great presentation by Keith Erskine with Emerson local business partner, Puffer-Sweiven and Fluor‘s Vince Mezzano on this topic, Regulators versus Control Valves: What’s the Best Fit?
Keith and Vince teamed up on a great article in Valve magazine also titled Regulators versus Control Valves: What’s the Best Fit? Their article’s executive summary:
For today’s up and coming engineers and plant designers, understanding the differences between what regulators can do and what control valves can do will be critical to making the best choices.
This educational article highlights how they differ, what each does, and their use in certain applications.
While both regulators and control valves are used in pressure control applications, they have unique differences:
The design of a typical control loop allows control valves to manipulate a range of process variables depending on which variable is measured for control. Examples of this include valves with capabilities for control of flow, level, temperature and pressure. The process control variable is measured by a sensor/transmitter and then communicated to a host control system, which is typically a distributed control system (DCS).
The main operational difference between a control valve and a regulator is that, contrary to the control loop design mentioned above, regulators are process-powered valves without the need for an external power or instrument air source to operate. A regulator typically applies the pressure of the controlled process fluid against a diaphragm. This diaphragm then opposes a compressed spring to achieve force balance with the diaphragm at a given set pressure.
Because pressure from the process is applied directly to a regulator’s diaphragm, inlet and outlet pressures must be considered in the design. Control valves can handle larger pipe sizes and higher pressures. They are also better suited for corrosive fluids since regulators will almost always have some elastomer material in contact with the process fluid. Regulators are much faster acting since they don’t have the latency of a control loop.
Here is a table of the relative advantages of the two technologies: Continue Reading ▶
If you’re not fluent in Polish, you may have missed a recent Automatyka
article, Bezpieczeństwo funkcjonalne zgodne z normami
[Functional Safety Compliance].
Emerson’s Andy Crosland
and Ryszard Boroń
wrote it and provided me an English translation of the article so that I could share with you. I’ve added some hyperlinks to some of the concepts, products, standards and regulations mentioned in the article.
Many believe Safety Integrity is all about component failure rates and complex calculations of probability of failure on demand. However, there are many ways to improve process safety without using a calculator, as this article explains.
International safety standards, IEC 61508 and IEC 61511, were developed as a direct result of several industrial process accidents. Applying the safety lifecycle approach described in IEC 61511 significantly reduces the likelihood of safety system failure.
Process operators face competing demands to maintain process safety, while at the same time meeting production targets. By June of this year (2015) all European Union Member States must implement the Seveso III directive into their own laws; changes from Seveso II stricter standards for inspections by government agencies and more effective enforcement of the rules for managing safety.
Inspectors look for evidence of good practice in process safety, with reference to IEC 61511 as the benchmark. Many experienced operators of hazardous process plants already manage safety to some extent. However, IEC 61511 calls for structure and planning, to ensure that nothing goes un-checked, and records should show that plans were followed and any resulting corrective actions completed. Producing documents to show functional safety is well-managed can be challenging, when the inspector calls. Continue Reading ▶
In the news every day we see the changes in economic activity in the upstream oil & gas exploration and production business caused by the significant drop in oil prices over the past several months.
But what have been the implications for downstream producers in the chemicals and specialty chemicals businesses? I caught up with Emerson’s Peter Cox
who leads the Chemicals industry group. He’s been closely following some of the analysis from organizations such as the American Chemistry Council
and the European Chemical Industry Council (Cefic)
Peter notes that the chemical industry, with its vast diversity ranging from production of oil-based petrochemicals and plastics to the high-tech specialty and consumer chemicals, has learned to live with the VUCA environment—Volatility, Uncertainty, Complexity and Ambiguity. It seems that it has been and will always be the order of the day in the chemical industry, but producers are becoming more clever and proactive in dealing with this current environment.
He describes some of the risks chemical producers face today beyond the drop in crude oil prices including geopolitical unrest and its many implications as well as China’s continuing growth slowdown and uncertain outlook. Production costs of basic chemicals and plastics are highly dependent upon the price of energy and energy-derived feedstocks. In the Americas, the American Chemistry Council reports that chemical production continues to expand.
The combination of both of these factors can represent as much as 75% of the total cost of the end product. Given this fact, lower oil prices are taking most chemical and polymers prices down worldwide. No doubt this will compress profit margins in commodity chemicals, even as input costs from oil and its derivatives decline. Continue Reading ▶
How often do you Google for a solution to a problem you face and land in an online community? It happens to me all the time. This was a lot of the reason for the creation of our Emerson Exchange 365 community several years ago—to provide a place where peer-to-peer problem solving could occur around all the Emerson Process Management technologies and solutions.
I mention this because I wanted to share a question and answer in the Measure & Analyze section’s Level group. The question involved guided wave radar (GWR) level measurement
technology [hyperlink added]:
I have a Rosemount 5300 Series Coaxial probe guided wave radar (HTHP type). I wanted to install it in place of a displacer in a displacer chamber. The original length of the probe assembly (Flange bottom to probe tip) was 762 mm. I reduced it to 693 mm to match my chamber’s height. The procedure for cutting the coaxial type probe is provided in Rosemount reference manual.
Before cutting away the extra length the transmitter was indicating the actual physical length of probe dipped in the liquid level, quite precisely. After cutting the probe to desired length I configured the new “probe length” and “Tank height” parameters in the transmitter. However, there is a constant error of about 10 to 15 mm in the indicated level.
Also there is a dead zone created of about 20 mm at the tip of the probe. In the dead zone the level is shown 0 mm regardless of the actual level.
Anybody having experience with this type of GWR please guide me about what other configurations I have to change to remove these errors?
Emerson’s Ingemar Serneby responded:
First of all, the HTHP seal contain dual ceramic seals and even though the ceramic is embedded in shock absorbents, it is essential that precautions are taken in order to protect the ceramics from damages while cutting the probe. Given that the seal still is intact, I recommend you to check the following: Check in the database that the probe type is correct. Note that the offset differ between the probe types and if you for instance erratically select “coaxial probe with a standard seal” while you have a “coaxial probe with HTHP-seal”, the measurement will be a couple of centimeters off.
Continue Reading ▶
It’s hard to read technology-based news sources without finding discussions on the Internet of Things (IoT). In looking at the Industrial Internet of Things (IIoT) from a process manufacturing and producing standpoint, wireless measurement devices play a big role IIoT.
I wanted to share a quick 2:12 YouTube video, Rosemount 248 Wireless Temperature Transmitter
featuring Emerson’s Cheng Vue
. Cheng introduces this new device which provides a cost effective solution for wireless process monitoring, based on the IEC 62591 WirelessHART communications standard.
He opens describing the 248 as a single input transmitter with an integral antenna and optional five-digit LCD display configured via a HART Field Communicator or AMS Device Manager.
He describes the housing that suitable for tough environments including offshore, salt-spray marine environments. The wireless temperature transmitter opens up many measurement opportunities that were previously difficult or impossible to reach due to location and available wiring infrastructure.
Cheng shows how field replacements can be made to the power module without removing the transmitter. For more on the specifications, here is the product data sheet and configuration data sheet. You can also contact a temperature measurement expert to discuss your application. Continue Reading ▶